Voltage doesn’t always mean that it has to be positive. That’s why a question arises can voltage be negative or not? Let’s feed your curiosity about negative voltage.

This article explains how a voltage can be negative, explaining the sign convention of voltage (according to basic circuit sign convention) in various circuitry, what causes the negative voltage, and converting any voltage to negative voltage.

Is voltage positive or negative?

  Voltage is the potential created between the two different points. Voltage can be elucidated as the work done per unit required to make a move for a unit charge from one point to another in presence of a static electric field.

 Voltage has magnitude and polarity. The polarity of the voltage can be negative or positive, where is the magnitude of voltage can only be positive. Voltage is a relative quantity, so that it can be positive as well as negative. 

 The concept of positive and negative voltage comes from the sign convention. The sign convention is a rule adopted globally to define electric flow or signs of electric power in a circuit. Benjamin Franklin was the one who surmised that electric flow from the positive terminal of voltage to the negative voltage terminal. At that time, the role of the electron in current flow was not clear the convention given by him to get accepted. Still, later on, after several discoveries, it was found that electron which causes current travel in the opposite direction of the current flow.

In-circuit zero volts are referred to as the ground, which is taken as a reference to measure other voltages. The voltage polarity of an electric circuit element varies for active or passive element for a passive element such as resistor The Terminal through which electron enters the element that terminal is the negative voltage terminal and another terminal of the component is the positive voltage terminal. For active components such as power supply and capacitor, the terminal that delivers current is the positive terminal, and the other terminal is the negative terminal.

What does it mean when voltage is negative?

Voltage is a relative quantity, so that it can be a negative or positive value.

When the voltage is more negative (in polarity) with respect to the circuit’s ground, then the voltage is negative. 

For example, a DC voltage source such as a battery (or cell) has a negative and positive terminal. When the battery’s positive terminal is founded, the negative terminal is connected to the circuitry then the voltage provided through the supply to the circuit is a negative voltage.

 The positive or negative voltage can be due to the orientation of voltage supplies in the circuitry. When the negative terminal is directly linked to the ground and the positive terminal is directly linked to the circuitry, the voltage generated is the positive voltage.  When the positive (+) terminal linked directly to the ground, and the negative (-) terminal is linked to the circuitry, the voltage generated out of the negative(-) terminal of supply is the negative voltage.

What is Negative Voltage used for

Several circuits use negative voltage, such as a transistor, Telecom, push-pull amplifier, a power driver circuit, etc.

Use of negative voltage:

 The operational amplifier (OpAmp) needs both positive and negative voltage for proper operation and amplification. For transistor biasing, a negative voltage is one requisite. In telecommunication, the lines are buried underground in the presence of moisture and other external material, which can cause corrosion in the wire, which is generally made of copper. When a negative voltage is used through the wire, it minimizes the corrosion.

Can Voltage Gain be Negative ?

Voltage gain is the ratio of output voltage (in volt) to the input voltage (in volt) of an circuit element.

Negative voltage gain means there is a change in polarity of the voltage from input to output. In other words, the output voltage is 180 degrees out of phase concerning the input. Voltage gain is negative when the output voltage is less (due to attenuation or phase shift) than that of the input voltage. A negative feedback amplifier has a negative voltage gain.

Can a battery voltage be negative?

Battery voltage polarity depends upon how it is connected between the circuitry and the ground.

Suppose the battery’s positive (+) terminal is directly linked to the ground and the negative (-) terminal is linked to the circuit. In that case, the voltage generated from it will be negative, and if the negative terminal is grounded.

The positive terminal is connected to the circuitry, then the voltage generated from it will be positive.

What is Negative Voltage in AC ?

In an alternating current (AC) circuit, two poles of the AC source interchanges between positive and negative.

The negative voltage in AC means the voltage is 180 degrees out of phase concerning the positive voltage. A complete cycle of AC consists of two half-cycle one is positive (+) half, and the other is the negative (-) half. The positive half is where the voltage is positive at any instant. Still, during the negative half of the circle, the polarity of voltage gets inverted with respect to the positive half of the cycle, which means at any instant of time during the negative half cycle, the voltage is negative.

Can Thevenin Voltage be Negative?

Thevenin voltage can be defined according to the Thevenin theorem, which states that any linear circuitry is a combination of several voltage sources, and resistors can be replaced by a resistor and a voltage source; the resulting voltage source is the Thevenin voltage.

The polarity of Thevenin voltage can be negative and positive depending upon the orientation of the Thevenin voltage in the circuitry. If the calculated Thevenin voltage is negative, that means the direction of the resultant power source will change. If the calculated value remains positive, then the orientation of the resulting power supply orientation is correct.

Can RMS Voltage be Negative ?

RMS stands for route mean square value. RMS voltage can be obtained by taking the square root of the mean value of squared instantaneous voltage over a time interval

The outcome of a square root can be negative or positive. Suppose the amplitude of the voltage is taken for the RMS, then by convention. In this case, the RMS of the voltage will only be positive if amplitude and phase of the voltage are taken for obtaining RMS voltage, then it can be a complex negative or positive value.

Can Node Voltage be Negative ?

In a circuit, the node is a point between two or more circuit elements, and node voltage is the electric potential difference between two nodes of the circuit.

Node voltage can be positive or negative as it is a relative quantity. One node of the circuit can be considered as a reference node, and with respect to that node, another node voltage can be measured. Generally, the reference voltage is the ground node, so the other node’s value depends on the direction of the current orientation, etc., with respect to the reference node. The measuring node voltage may be inferior than that of the reference voltage.

Can Stopping Voltage be Negative ?

In the Photoelectric effect experiment, the anode is the target material. The anode is connected to the positive terminal of the voltage source while exposed to the monochromatic and electromagnetic wave, which results in current flow through the circuit current is called photocurrent.

When the anode is linked to the negative terminal of the voltage source, as the voltage increases, the photocurrent dies out. The voltage at which the photocurrent stops flowing through the circuit is known as the stopping voltage. Through this experiment, we got to know that the stopping voltage is a negative value.

Can Peak to Peak Voltage be Negative ?

Peak to peak voltage is the difference between minimum voltage and a maximum voltage of a voltage signal.

The magnitude of the peak to peak voltage can vary from 0 to any positive value as the polarity of peak to peak voltage can be negative and positive.

Can Instantaneous Voltage be Negative ?

Instantaneous voltage is the value of the voltage ( or potential difference) at a particular moment of time.

Instantaneous voltage can be negative or positive. The instantaneous voltage of a negative DC voltage source is consistently negative at any instant of time. In AC voltage, the instantaneous voltage varies from positive to negative with time. For the negative cycle of the AC voltage signal, the instantaneous value of the voltage is negative at any instant in time.

Is Current Negative if Voltage is Negative?

Voltage is a relative quantity so that it can be negative. Negative current can only mean the direction of electron current, which is opposite to the electrical current as of the convention.

Negative voltage means the supply’s negative terminal is directly connected to the circuitry, and the positive terminal is grounded. The current from the negative(-) terminal of the voltage source is taken into consideration . That current will be the negative current as we know the electrical current from the positive terminal of any voltage supply.

What does Negative 5 Volts mean?

5 volt is a potential difference (or voltage) between two different points. Acknowledge that voltage is a relative quantity, the polarity of the voltage can change considering the references.

When the positive terminal of the 5 DC volt supply is directly linked to the ground. As a result, the positive (+) terminal becomes the reference voltage, and the negative (-) terminal of the 5 volt supply is linked to the circuitry. The resultant voltage through the 5 volt supply will be negative 5 volts as the positive terminal is taken as the reference point.

How do you create a Negative Voltage?

Different methods can be used to generate a negative voltage.

Using :-

With the combination of 555 timers and a clipper circuit, the negative voltage can be generated as output. Here 555 timer act as an astable vibrator. After receiving power from the power supply, 555 will generate a square wave as an output, which will consist of both positive and negative voltage. During the positive half of the output voltage, the capacitor connected with the output gets charged, so there will be no positive voltage. During the negative voltage at the capacitor gets discharged through the diode providing negative voltage as output.

There are several ICS that uses switched capacitor voltage converter to convert a voltage into a negative voltage. Generally, these IC contains non-critical capacitors for the charge pump and charge reservoir. And as the fundamental component of these ICs is oscillator voltage level translator and MOS switches.

As we know half-wave rectifier can filter out positive or negative half of any AC signal as required output is the negative voltage negative half-wave rectifier can be used in this rectifier only negative half of the AC signal can pass through it so as a result, there will only be the negative voltage as output

The voltage gain of inverting amplifier is negative, which means the output of the inverting amplifier is 180 degrees out of phase with the input of the amplifier, so if a positive voltage is fed into the inverting, amplifier, then the negative voltage will be as output.

How do you convert Negative Voltage to Positive?

Negative voltage can be converted into positive voltage as a requirement.

Inverting amplifier can be used to transform the negative (-) voltage into positive(+) voltage. The voltage gain of the inverting amplifier is negative, which means the output voltage is 180 degrees out of phase concerning the input. If the input is taken as a negative voltage, then the output voltage of the inverting amplifier will be positive.

What are Negative Voltage Regulators?

Voltage regulators are used to maintaining a specific range of voltage for different purposes.

A negative voltage regulator is a circuit that is used to maintain the voltage of any specific negative voltage range. 79XX is an IC family which is a three-pin negative voltage regulator.

These ICs are available in 3 different output voltages -5, -12, and – 15. These integrated circuits have intercurrent limiting properties and thermal shutdown protection for their safety.

Can Arduino Output Negative Voltage?

There are several Arduino boards available commercially.

Generally, the output voltage directly from Arduino is in the positive voltage range. The voltage range will vary from one type to another or the pin from which output is taken. For getting negative voltage output from Arduino, external voltage converter circuitry is required for the voltage conversion from positive to negative.

Is Ground Positive or Negative?

The ground is the reference point of the circuitry with respect to which the voltage of any point can be measured.

The ground can be positive as well as negative depending upon the design of the circuitry. In electronics, a positive or a negative terminal of any power supply can be considered the ground. When the supply’s negative terminal is directly connected to the ground, then the ground is called negative ground. When the supply’s positive terminal is directly connected to the ground, then the ground is called positive ground.

Can you Connect Ground to Negative?

The voltage source has two terminals; one is considered positive, and the other is negative.

The ground is the Zero Volt reference point of the circuit. If there is only one supply in the circuit, then the supply’s negative terminal is considered the same as the ground. If required, the ground can also be linked directly to the negative (-) terminal of the DC supply. When the DC terminal is directly connected to the ground, then the ground is called negative ground. There is no positive or negative end in AC supply as polarity changes with time, so a neutral wire from the AC circuit can be directly connected to the ground. The ground is not necessary for every circuit. It is generally used for protection, a common reference point for voltages, etc.

How do you test a Negative Voltage Regulator?

The output and input voltage of the regulator can check for testing the negative voltage regulator.

The input voltage to the negative regulator can be measured with respect to the ground; the regulator’s input voltage is tested so that the regulator can work appropriately with sufficient input voltage. The input voltage must be greater than that of the regulated output voltage in magnitude. The output voltage range differ with distinct voltage regulators. As for the negative voltage regulator, the output voltage range will be in negative voltage values. When a negative voltage regulator is tested, ensure the output voltage is in the negative voltage range. The voltage output must be nearby its rated output voltage. If the output voltage is not around the rated output, then the regulator may be defective.

Which IC is used to get Negative Voltage?

Switched capacitor voltage converter that inverts, divides, doubles, or multiples, the positive input voltage.

IC’s used to get the negative voltage as output are TL7660, MAX1044, NCP1729, LT1026, MAX870, MAX829, LT1054, CAT7660, etc. These IC’s are used in line drivers, operational amplifiers, suppliers, negative voltage generators, voltage splitters, voltage developers, etc. These ICs work for a different range of voltage that’s depends on the specifications of the IC.

Why does Current Flow from Negative to Positive?

The potential difference between the two points in the circuit is the flow of current.

The electron current begins from the negative (-) terminal. It travels to the supply’s positive terminal, as the electron current is in the contradictory direction of the electric convention of current. The flow of electrons is caused by the difference in polarity or the potential difference created by the excess of the electron at one end and the deficiency of electron at other—negatively charged electrons drawn towards the positive end of the supply from the negative end the supply.

What is difference between Positive and Negative Voltage?

Any voltage can be either positive, negative, or zero.

The difference between positive (+) and negative (-) voltage is in the polarity of the voltage. The polarity of the voltage can change with the reference as if a higher potential point is taken as a reference to measure the lower potential. The potential difference will be negative, which is the negative voltage. And when a lower potential point is taken as a reference to measure the higher potential, the potential difference will be positive. The polarity of voltage also influenced the orientation of the DC source. For AC source with time, the polarity of the voltage changes as for the positive half of the AC signal, the voltage is positive, and for the negative half, the voltage is negative.

Content:

• What is a Filter Capacitor?
• Filter Capacitor Applications
• Filter Capacitor Circuit to Block DC and Pass AC
• DC filter capacitor calculation
• Filter capacitor in rectifier
• Filter capacitor for bridge rectifier
• Filter capacitor value calculation
• Low pass filter capacitor
• Bypass filter capacitor
• High frequency filter capacitor
• 3 terminal filter capacitor
• Harmonic filter capacitor
• Feedthrough filter capacitor
• Line filter capacitor
• Alternator filter capacitor
• Electrolytic filter capacitor
• EMI filter capacitor
• Filter capacitor design
• Filter capacitor amplifier
• Filter capacitor selection
• High voltage filter capacitor
• How to test filter capacitors
• SMD filter capacitor
• FAQ

What is a Filter Capacitor?

The capacitor’s impedance can be defined as a function of frequency as the capacitor is a reactive element, it is suitable for using it as an analog electronics filter.

A filter capacitor is a passive filter that consists of the passive element. Capacitor effects of any signal are frequency-dependent. This capacitor characteristic is used to design filters that can filter out a specific frequency range of signals as required.

Filter Capacitor Image

Working of Filter Capacitor

The capacitor is a reactive circuit element; its impedance and resistance will vary with the frequency signal passing through it.

The working of the filter-capacitor is based on the fundamental principle of capacitive reactance. The value of capacitive reactance changes with the frequency applied to the capacitor for lower frequency signal capacitor offers a higher resistance, and higher frequency signal capacitor provides low resistance. The capacitor is always trying to maintain the capacitance of the capacitor, so the capacitor will try to resist small current flow in the circuit creates capacitor impedance.

Filter Capacitor Replacement

The filter-capacitor can be replaced by Active Capacitor, Inductor filter circuit, FET circuits, etc.

Filter Capacitor Types

The filter-capacitor can be classified as following as basic types:

• Low Pass capacitor-filter
• High pass capacitor-filter
• Bandpass capacitor-filter
• Bandstop / Band Reject capacitor-filter

Filter Capacitor Formula

As we got to know, there is a relationship between the capacitor’s capacitive reactance (X_c) with the capacitor’s input signal frequency and capacitance.

X_c=1/ (2πfC)

So, the capacitive reactance (X_c) of the filter capacitor is inversely proportional to the frequency (f) of the signal. 

Filter Capacitor Circuit

Filter Capacitor Applications

The filter-capacitor is used in various applications such as:

• Block the DC or AC component of the signal.
• Bypass DC or AC part of the signal.
• High voltage filter applications.
• To limit the frequency band.
• To remove unwanted noise from the circuit.
• To remove interference in circuitry.
• It is used to remove radio noise.

Filter Capacitor Circuit to Block DC and Pass AC

When a capacitor is connected to a series with the DC source in a completely discharged state, the current will flow until the capacitor is fully charged. At that stage, the capacitor voltage is equal to the applied voltage, and at that point, the capacitor is saturated now no current can flow through it, so the capacitor will behave as an open circuit. As we know, DC usually e is a constant value that is it has 0Hz frequency. As the capacitor offers high resistance towards low frequency, when the capacitor is connected in series with the DC source, it will block all the DC components from the signal and let AC pass through it.

DC filter capacitor calculation

As we know, the DC signal is usually a constant value, I.e. it has 0 Hz frequency.

Now X_c=1/ (2πcf) as f=0

X_c= ∞

So for the DC input, the capacitor provides infinite resistance, so I = V/X_c

 As for the value of X_c= ∞, the value of I=0.

Filter Capacitor in Rectifier

The output of the rectifier is pulsating in nature which makes it suitable for DC supply in the electronic circuit, so the capacitor is connected across the load. The filter-capacitor helps to reduce the pulsating behaviour of the rectifier output.

  In a half rectifier circuit, one ideal diode in the voltage source is an AC source with a sinusoidal signal in the positive half of the signal. The diode is in forward bias, so the diode is forward biased, and the capacitor got charged. In the negative half of the signal, the diode is in reverse bias, so no current flow through the diode, and the charged capacitor will discharge through the load resistor, that’s how the filter capacitor reduces the pulsating nature of the output of the rectifier.

To keep the output voltage from reducing too much during capacitor discharge, select a capacitor with a value so that time constant is much higher than the discharge interval. The filter-capacitor is connected in parallel with the load, so this filter circuit is also known as a shunt capacitor-filter. A capacitor is of the larger value connected across the load impedance.

Filter Capacitor for Bridge Rectifier

A bridge rectifier converts AC to DC by using four diodes same as the half-bridge rectifier. The output is pulsating in nature, so a capacitor is connected across the load to make a more pure DC form. The working is the same as the half rectifier filter circuit. The main advantage of a full-wave bridge rectifier is that its output is less pulsating behaviour than that of the half-wave rectifier, so the capacitor size in bridge filter circuit can be smaller than that of the half-wave filter-capacitor.

Filter Capacitor Value Calculation

How to calculate the filter capacitor value in power supply ?

The relation between the capacitance of Capacitor (C) with change (Q) and voltage (V) across the capacitor is defined as C=QV

The relation between the charge and the current is Q= IT

As we know that time is inversely proportional to the time T=1/f

For the above equations, we get C=I/(FV)

Low Pass Filter Capacitor

Low pass filter only passes the frequency signal, which is lower than that of the filter’s cutoff frequency. For this low pass filter, the relationship between capacitor resistance and the cutoff frequency is

f_c = 1/(2πRC)

The resistor in the circuit is independent of the variation of the applied frequency, but the capacitor is sensitive to the changes in the input signal frequency.

When the input signal frequency is low, the capacitor’s impedance is higher than the impedance of the resistor to the input voltage drop across the capacitor. Still, when the input signal frequency is high, then the capacitor’s impedance is lower than that of the resistor does more voltage drop across the resistor. Low frequency gets passed through, and high frequency gets blocked.

 In a low pass filter, the frequencies below the cutoff frequency are known as passband, and the frequency above the cutoff frequency is known as stopband.

Low pass filters are used for

• To reduce electrical noise
• To limit the bandwidth of the signal
• To reduce interference

The gain of the low-pass filter in magnitude can be calculated by

Gain of filter = 20log (Vout/Vin)

Vout-> output voltage of the filter

Vin-> input voltage of the filter

Low Pass Filter Capacitor Type

It can be of two type:

• First Order Filter-Capacitor
• Second Order Filter-Capacitor

The low pass filter circuit above has only one reactive component capacitor, called one poll filter or first-order filter.

In the second-order of the low pass filter, it has to the reactive element that is capacitor in its circuit does design is helpful when the signal does not provide a wideband range between desired and undesired frequency components.

Bypass Filter Capacitor

Here one end of the capacitor is linked to the power supply, and the other is linked directly to the ground. This capacitor helps to reduce the effect of voltage spikes or any AC component from the power supply; it shorts the AC signal to the ground and reduces AC noise to produce a much clear DC signal.

The capacitor in this circuit must have at least one-tenth of resistance as that of the resister Re. As we know, electric current chooses the path with a low resistance to following if it has multiple paths to choose from is; the capacitor offers great resistance to low frequency, so only the AC component of the signal passes through it. The DC component of the input signal will pass through the resistor Re.

High Frequency Filter Capacitor

A high pass filter is a filter that blocks low frequency and let pass through the higher frequency signal here. The frequency lower than the cutoff frequency is blocked, and the frequency higher than the cutoff frequency allowed to pass through this filter is also called a low cut filter. A capacitor is linked in series with the input supply; the resistor is linked in parallel.

 As we know, when the frequency of the input signal is low, the capacitor’s impedance is higher as the capacitor is in series with the power supply through which only a high-frequency signal can pass it.

The above circuit is a first-order high pass capacitor filter as there is only one reactive element in that circuit.

The second-order high pass capacitor-filter and the first order high pass capacitor filter are cascaded together to form a second-order high pass capacitor-filter.

3 Terminal Filter Capacitor

Three terminal capacitor-filters consist of a three-terminal capacitor, which features a more negligible impedance than two terminal capacitors. Which allows it to reduce the impedance in the higher frequency band with lesser number of the reactive element it has great noise suppression effect these are used in power lines of circuit, smartphones, LED TV etc.

Harmonic Filter Capacitor

The harmonic filter can be designed of series or parallel reactive elements to block or shunt the harmonic currents. They can be available in several shapes and sizes. Still, when this capacitor is connected in parallel with the power supply, it helps reduce harmonic current and voltage in the circuitry.

The capacitor required in the harmonic filter must accept the given magnitude of various orders of harmonic current. A harmonic current can be a non-sine wave since the capacitor is very sensitive towards the high tension value. The capacitor is used in the harmonic filter in specific ranges depending upon the capacitor in use. A harmonic filter is formed by a capacitor bank, mainly a group of capacitors of the same rating. This filter converts the harmonic current into heat to protect the load from it.

Feedthrough Filter Capacitor

The feedthrough filter-capacitor is a three-terminal capacitor whose grounding impedance is a small and low effect on the lead impedance. It is specially designed for more efficient performance in filtering circuit.

 The ordinary capacitor is not very good for filter application as they have a high impedance which is undesirable and can affect the efficiency of the filtering circuit feedthrough filter capacitor has a small value of shunt capacitance. This capacitor is used in AC and DC supply lines to reduce harmful interference.

The feedthrough filter-capacitor has a filtering effect close to that of an ideal capacitor. The capacitor was initially designed for DC power lines in the RF system, blocking RF energy and letting DC signals pass through it.

Line Filter Capacitor

The line filter capacitor is a capacitor used to suppress electrical noise generated from the power supply.

 The power supply can have various disturbances that include transient surges and fluctuations in its supply voltage. To reduce the effect of such noise, line filter capacitors use line filter capacitors that can endure fluctuations or transients for a more extended period without falling into it.

Line filter capacitor is used to

• keep potentially damaging line transients
• To reduce line disturbance produced by the source
• To reduce the circuit generated noise

 There are two topologies used in the line filter: one is an X capacitor, and the other is a Y capacitor.

 In X Capacitor, here capacitor is connected across the line supply X capacitor is used where cellular could not lead to an electric shock. It eliminated the electrical noise coming from the power supply and made it used in high-frequency applications. The capacitance of X capacitor can range from 1microF to 10MicroF.

Y capacitor,  in this topology, capacitors are connected between the line voltage supply and the chassis of the appliances list of colleges used for an application that could lead to electrical shock. The range of this capacitor can be from 0.001 micro F to 1micro F.

Filter Capacitor in a Power Supply Circuit

Alternator Filter Capacitor

Alternator stator windings generate the current 3 phase AC. There is not much ripple voltage to produce radio noise. A diode converts the AC to DC, and if any alternator diode fails, the ripple voltage will increase, or noise can be caused by those who have electrical connections. Still, a filter-capacitor can be used to minimize the noise in the circuit. The filter-capacitor can either block the unwanted AC voltage or bypass the unwanted AC voltage back to the source.

Electrolytic Filter Capacitor

An electrolytic capacitor is a capacitor whose positive plate is made of metal and covered by an insulating oxide layer over the metal. This capacitor uses an electrolyte to have a massive capacitance than other capacitors. The capacitor is used in a filter circuit that combines AC power DC voltage electrolytic capacitor filter to eliminate 60 Hz to 120 Hz AC ripple in DC power supply.

EMI Filter Capacitor

Capacitors used in filtering electromagnetic interference in AC and DC power lines are known as EMI filter capacitors. This capacitor can fail due to over-voltage and transients. There are two different types of topology used in filter capacitor X, and Y.  X capacitor topology is used for differential mode EMI filtering. In contrast, Y capacitor topology is used in standard mode EMI filtering.

Theoretically, several capacitor technologies design X or Y capacitors, but the most commercially available are film capacitors or ceramic capacitors.

Filter Capacitor Design

Filter capacitors can be designed in different ways as per requirement.

 When a low pass filter is created, the capacitor is then connected across the load. When a high pass filter is designed, the filter-capacitor is in series with a power supply. The capacitor-filter is used as a bypass filter when the capacitor is connected between the ground and power supply. Different filter capacitors can be designed based on the different ranges of operations, costs, decisions, operating temperatures and sizes.

Filter Capacitor Amplifier

The filter capacitor has a great disadvantage: the amplitude of the output signal is lower than that of the input signal due to an attenuation of the signal. This means the overall gain of the filter-capacitor is less than one, so there may be a need to amplify the output signal.

 Different amplifiers can be used to restore or control the attenuated signal, such as OpAmp, transistors or FETs. After the capacitor-filter amplifier can draw power from an external source to boost or amplifier the output signal through the capacitor-filter, the output signal of the capacitor-filter can be altered or reshaped as required by the amplifier circuit.

Filter Capacitor Selection

How to select filter capacitor value ?

Select the capacitor-filter based on:

• Cost
• Precision
• Range of operation
• Stability
• Leakage current
• Size
• Operating temperature

High Voltage Filter Capacitor

High Voltage capacitor passive circuit component that can store charge and energy for use in High Voltage application, ordinary capacitor cannot be used in high voltage applications so high voltage capacitor used in higher voltage range application such as high voltage power line filtering, high voltage AC or DC filtering, high voltage AC or DC bypass, etc. These capacitors are designed where the two metal plates of the capacitor are separated by dielectric metal in between for efficient operation in high voltage application.

How to Test Filter Capacitor

There are two ways to check the filter-capacitor:

1. Before checking the capacitor, make sure the capacitor is fully discharged. If it is not fully discharged, then discharge the capacitor by connecting it through a load. If you are using a multimeter, then set the metre to read high ohm range. Correctly connect the positive and negative end of the capacitor with the multimeter. The meter should begin from 0 and then move towards infinity, that shows the capacitor is in working condition; if the meter stays at 0, then the capacitor is not charging through the meter, that shows it is not working properly.
2. Another way to test the filter capacitor, charge the capacitor with the DC voltage supply and then observe the voltage across the anode and cathode of the capacitor. In this test, the capacitor’s polarity is essential just before applying the voltage. Check the capacitor after charging, disconnect the voltage source from the capacitor, and use a multimeter to observe the voltage on the capacitor. Upon checking, the charged capacitor must hold the voltage applied. The voltage will rapidly drop to zero when the multimeter is connected because the capacitor will be discharging through the multimeter. If the capacitor is not holding any value near the applied voltage, then the capacitor is not working correctly.

SMD filter capacitor

SMD stands for surface mounted device which means SMD capacitor is the surface-mounted capacitor nowadays SMD capacitor is widely in use as a filter because they are smaller in size and can be placed easily on the circuit board surface mounted technology allows faster and reliable construction of Electronic element, so it is capacitor are readily available and having cheaper and higher performance.

FAQ

What does a filter capacitor do ?

Filter-capacitors can be used for different purposes with different arrangements in the circuit.

The filter-capacitor can be used to restrict the DC component of the input signal. It can also reject or bypass the AC component of the input signal. Filter-capacitors can limit the signal’s bandwidth or remove a specific range of frequency from the signal. It can also be used to remove unwanted components or noise from the circuitry.

How to select filter capacitors?

Select the capacitor-filter based on:

• Cost
• Precision
• Range of operation
• Stability
• Leakage current
• Size
• Operating temperature

What is the effect of a capacitor as a filter?

The capacitor is used as a filter. It can filter out AC or DC components from the signal or eliminate a specific frequency range.

Capacitor offers high resistance towards the low-frequency input signal. In contrast, it offers low resistance to the high-frequency signal, so when the capacitor is connected in series with the power signal, only the AC component can pass through that. Only the DC component can passes through the load when the capacitor is linked in parallel to the load.

What are the advantages and disadvantages of capacitor filter?

There are several advantages and disadvantages of capacitor filters.

The advantages of capacitor-filters are cheaper, smaller in size, readily available. The disadvantages of the filter-capacitor are that it is sensitive to temperature change, its capacitance reduces with time.

What happens when filter capacitor value is larger?

The larger the filter-capacitor value, the size of the capacitor also increases with it.

With a larger filter capacitor, the voltage will be minimal. The time constant will be large. The charge will be maintained for a longer period, but it will draw a large amount of current and take a long time to complete the charge and be expensive.

Which one is best either capacitor filter or inductor filter?

The filter can be designed with either a Capacitor or Inductor or by using both.

Capacitor-filters are cheaper than inductor fitters. The size of the filter-capacitor is always less than the size of the inductor filter. The capacitor-filter is better at a smoothening voltage, whereas the inductor filter is better at smoothing current.

Which type of capacitor is used in a low-pass filter?

In a low pass filter, the capacitor is connected across the load.

The type of capacitor used in low pass filter depends on the operating range, temperature, sensitivity, stability, cost, size, etc. The capacitor, which fulfils the requirements, can be used.

What is the difference between a rail and a filter capacitor in a circuit?

A rail capacitor is used in power rail, and the filter capacitor is used for different purposes.

A rail capacitor is used to filter out the noise or ripple in the rail power line. This capacitor is mainly used to maintain the voltage in its rated value and to stabilize it. Where is the filter capacitor used for different purposes such as to eliminate the AC component of the signal, block DC component signal, as bypass filter, EMI filter, limit the bandwidth of the signal, eliminate a specific range of the signal, etc.

Why do we use capacitors as filters in rectification when capacitors are used to block DC and allow AC?

When we use a filter-capacitor in the rectification circuit, it only reduces the AC component of the signal.

In the rectifier circuit, the filter-capacitor is linked in parallel to the load appliances circuit. The DC component of the input signal can pass through the load, and the AC component of the input signal will pass through the filter capacitor. The capacitor shows low resistance towards the high-frequency signal.

What is the effect of filter capacitance magnitudes on the ripple voltage in DC power supplies?

When the filter-capacitor is connected in series with the DC power supply, it reduces the power supply’s AC component.

 A filter-capacitor is used in circuitry to minimize the ripple voltage of the power supply.

The ripple voltage output from the filter can be calculated by 

V_r= V_p/(2fCR)

Where V_r =ripple voltage

V_p = peak voltage

f= frequency of the signal (supply)

C= Capacitance of the Capacitator

R= the value of the resistance

Shift Register using D flip flop

A flip flop is also a single register that can store one bit when a register is designed with multiple flip flops, which can hold more bit data. Finally, a shift register is a type of logic circuit used to store or transfer data.

The shift register is designed with different numbers of flip flops, where data can be conveyed from left to right or right to left. It can have parallel input or serial input and serial output or parallel output. The shift register can also be designed with D flip flops also.

Serial In Serial Out Shift Register using D flip flop

In this type of register, the input is serial one bit at a time, and output is also serial one bit in a serial sequence.

Each flip flop can store one bit at a time, so for a 4-bit shift register, four flip flops are needed. As shown above, serial data is applied through D of the 1st Flip flop to all remaining flip flops. When a series of data feeds to the register, each bit is provided to the next flip flop with every positive edge of the clock pulse, and with every clock pulse, the serial data moves from one flip flop to the next flip flop.

2 Bit Shift Register using D flip flop

The following diagram is the diagram of a 2-bit shift register that can store or transfer 2-bit data. Where input data and output data are both in serial sequence, so it is a Serial in Serial out (SISO) shift register of two-bit, the process of entering data begins with the lowest significant bit of the register, the data input enters the register with every positive edge of the clock pulse.

Disadvantages of SISO:

Parallel In Serial Out Shift Register using D flip flop

Here are four different data lines for the 4-bit shift register; each D flip flop has its separate input. Data is fed into the respective registers in a parallel way. With every clock pulse, the data bits are shifted towards the output Z. here, and the output comes out in the serial sequence form. Parallel in Serial Out (PISO) shift register can be of two types of data loading: synchronous loading and asynchronous loading. With this shift register, the data in parallel form can be converted into the serial form of data.

4 bit Bidirectional Shift Register using D flip flop

A 4-bit bidirectional shift register is a type of shift register in which data bits can be shifted from left to right or right to left as per requirement. When the Right/Left is high, the circuit works as a right shift register, and when it’s low, this circuit acts as a left shift register, and the data shift with every positive edge of the clock pulse in this type of register.

4 bit Universal Shift Register using D flip flop

It is a bidirectional shift register, where input can be fed in serial or parallel ways, and output can also be in serial or parallel. That’s why it is called a universal shift register. Moreover, it can be developed with a D flip-flop, as shown in the given figure of the universal shift register.

8 bit Register D flip flop

The 8-bit register can be designed with an 8 D flip flop.

D type flip flop Counter

The counter can be designed with a D flip flop; the number of flip flops depends on the number of bit counters to be developed. In addition, both synchronous and asynchronous counters can be created with the d flip flop.

Counter circuit D flip flop

A counter is a group of flip flops whose state changes with every clock pulse applied. The counter is used to count pulses, form waveform, generate a required sequence, etc.

A counter can be a synchronous or asynchronous counter. The ripple counter is an asynchronous type counter. Several states that counter that pass through before returning to the initial state are called the counter’s modulus.

D flip flop up Counter

The counter starts from the minimum digit value of a counter according to the number of flip flops used to design the counter and goes to the maximum capacity of the counter with every clock pulse. So that is an up counter.

D flip flop Down Counter

The counter starts from the maximum value of the digit according to the number of flip flops used in the counter and goes down to the minimum digit value of the counter. So that’s down the counter.

D flip flop Asynchronous Counter

In this type of counter, each Flip Flop has a different clock pulse; the output of this type of counter is independent of a clock pulse; here, the output of a flip flop can be fed into the next flip flop as a clock pulse.

Ripple Counter using D flip flop | Asynchronous D flip flop Counter

Ripple counter, or asynchronous counter, is the simplest form of counter, which is very simple to design and requires very little hardware. However, Flip Flop does not operate simultaneously; each Flip Flop works at different time instances, and each Flip Flop toggles with a clock pulse. Therefore, to design a ripple counter from a d flip flop, the d flip flop must be in a toggle state so that with every clock pulse, it toggles.

4 bit Binary Ripple Counter using D flip flop

3 bit D flip flop Counter Asynchronous Up Counter using d flip flop

 

2 bit Binary Counter using D flip flop

3 bit Asynchronous Down Counter using D flip flop

Decade Counter using D flip flop

A decade counter is a counter which can count up to 9, the counter starts from 0, and with every clock pulse, it counts up to nine, and when it reaches nine, it resets itself to 0.

BCD Counter using D flip flop

Mod 3 Counter using D flip flop

Mod 5 Asynchronous Counter using D flip flop

Mod 6 Asynchronous Counter using D flip flop

Mod 7 Counter using D flip flop

Ring Counter using D flip flop

A ring counter is a synchronous counter, where the number is a maximum bit that can be counted depending on the number of flip flops used in the circuit. Here, each flip flop operates simultaneously; the output of a flip flop feeds into the next flip flop as input, where the last flip flop’s output is provided to the first flip flop as input.

Two bit Counter D flip flop   

4 bit Ring Counter using D flip flop|4 bit Binary Synchronous Counter with D flip flop

5 bit Ring Counter using D flip flop

2 bit Up Down Counter with D flip flops

3 Bit Synchronous Counter using D flip flop

3 bit Synchronous Up Down Counter using D flip flop

4 bit Synchronous Up Down Counter using D flip flop

2 bit Synchronous Counter using D flip flop

4 bit Down Counter using D flip flop

4 bit Synchronous Up Counter using D flip flop

Design 3 bit Synchronous Counter using D flip flop 

Johnson Counter Using D flip flop

Mod 6 Synchronous Counter using D flip flop

Mod 6 Synchronous Counter using D flip flop Truth Table

Q1	Q2	Q3	RESET
0	0	0	0
0	0	1	0
0	1	0	0
0	1	1	0
1	0	0	0
1	0	1	0
1	1	0	1

Mod 10 Synchronous Counter using D flip flop

Mod 12 Synchronous Counter using D flip flop

Mod 8 Synchronous Counter D flip flop

Sequence Generator using D flip flop

A sequence generator is used to generate the required sequence as output; the output set may vary with the requirements, and the series’s length is also very. It can be designed with counters to achieve the required output sequence using different counters with different gates. The sequence generator is used for coding and control.

Pseudo Random Sequence Generator using D flip flop

The pseudo noise sequence is not truly random; it is a periodic binary sequence with finite length to be determined. The PN sequence generator can be designed with a linear feedback shift register, whereas in the shift register, the data is shifted from left to right with each clock cycle.

Pseudo noise sequence generator is designed with D flip flop and XOR gate; here the bit got shifted from left to right with clock, the output of the 3rd D flip flop and the output of the 2nd D flip flop are XORed together and feed as input to the 1st D flip flop. The PN sequence increases with the number of flip flops used.

Double Edge Triggered D flip flop

Double Edge or Dual Edge triggered D flip flop is a type of sequential circuit that can select data from the clock pulse’s positive and negative edge. Double edge triggered D flip flop can be designed from two D flip flop one is positive. The other is a negative edge triggered D flip flop connected to a 2:1 multiplexer, wherein the multiplexer clock pulse acts as the select line. The positive edge D flip flop output is fed into one input data, and the negative edge d flip flop output is fed into the other input data of the multiplexer.

Traffic Light Controller using D flip flops

Traffic light controller can be designed with d flip flop, as shown in the given figure, Qbar of the 2nd D flip flop powers the red light. Whereas Q from 1st D flip flop provides power to the Yellow light, the green light gets power when the AND gate is high.

Both D flip flops are in toggle states when the clock is high, and the flip flop toggles when there is no clock; the flip flop is in a hold state. The time duration of each light can be controlled with the clock frequency; for different requirements, the clock pulse frequency can be changed.

Conversion of T flip flop to D flip flop

D flip flop can also be designed with a T flip flop when the output of the T flip flop is feed in ]to an XOR gated with Data input, and the output of XOR gate connected to the input of the T flip flop.

Convert SR Flip Flop to D Flip Flop

Data (D) will be the external input for the flip flop, whereas S and R of SR flip flop are expressed in D, S gets data input, whereas R gets inverted data input.

Conversion of D flip flop to JK

 JK flip flop can be designed with a D flip flop by adding a combinational circuit to the input of the D flip flop, as shown in the given figure.

J	K	Qn	Qn+1	D
0	0	0	0	0
0	0	1	1	1
0	1	0	0	0
0	1	1	0	0
1	0	0	1	1
1	0	1	1	1
1	1	0	1	1
1	1	1	0	0

JK Flip Flop using D Flip Flop and Multiplexer

JK flip flops can be designed with a d flip flop and a multiplexer. As shown in the figure, the output Q of the d flip flop is used as a select signal of the multiplexer. Thus, J and K are the input to the multiplexer, whereas J input with an inverter to the multiplexer. The multiplexer used here is 2: 1 MUX; the output of the MUX is acted as the input to the D flip flop as Q changes the select line of the MUX changes accordingly.

Conversion of D flip flop to T flip flop

The D flip flop should toggle with every high input to convert the D flip flop into a T flip flop. So for that, an XOR gate is connected to the D flip flop, T will be the external input to the XOR gate, and the output of the D flip flop will be the other input of the XOR gate.

T flip flop using D flip flop Truth Table

D	Qn	Qn+1	T
0	0	0	0
0	1	0	1
1	0	1	1
1	1	1	0

D flip flop to SR flip flop

An SR flip flop can be designed with a D flip flop in addition to a combinational circuit, as shown in the given figure. One OR gate AND gate and NOT gates are used to create the additional combinational circuit.

D flip flop Toggle Switch

The toggle switch circuit uses a push-button; when the first button press happens, the output will hold into the active, and the output will be held to active or in on state until the next button press happens. I.e., whenever the button is pressed, the output toggles, which can be designed with a D flip flop with a relay switch. D flip flop should be in a toggle state, which can be created by adding the Qbar output of the Flip flop feedback to the D input.

Advantages and Disadvantages of D flip flop

Advantages:

Disadvantages:

D flip flop IC

IC stands for an integrated circuit, whereas D flip flop IC means the integrated circuit of D flip flop.D Flip Flop is commercially available in both TTL and CMOS packages format with the majority familiar being the 74LS74 (D flip flop IC) which is a Dual D flip-flop IC, different IC of D flip flops has different IC numbers, and some IC contains eight d flip flops, six d flip flops,  two d flip flops, etc. Moreover, some IC has set and preset pin with the flip flops, some IC has Q compliment as pin output, some IC can contain edge-triggered D flip flops, etc.

D flip flop IC number

74HC74, 74LS75, 74HC174, 74HC175, 74HC273, 74HC373, 74HC374A, 74LVC1G79, 74LVC1G74, 74LVC1G175, 74LVC1G80, 74LS74, 7474, CD4013, etc. These are all different types of D flip flop IC.

Single D flip flop IC

A single D flip flop is available on an Integrated circuit. this D flip flop IC contains eight pins, one for data input, one for the clock signal, one for the voltage source, one for ground, one output, one clear, one preset, and one complimentary output Q. It consumes low power and has high noise immunity, and can be packed in any package as it has multiple packaging options. These IC can be used in different applications such as Motor Drives, Telecom Infrastructure, Tests and Measurements, etc.

Single D flip flop IC number

74LVC1G79, 74LVC1G74, 74LVC1G175, 74LVC1G80, SN74LVC1G80, NL17SZ74, NLX1G74, These are some IC number which contains single d flip flop.

Dual D flip flop IC

Two D flip-flops are available in Integrated circuit (IC) form. this D flip flop IC has 14 pins in its integrated circuitry, containing separate input and output for each d flip flops like data input, Q output, and Qbar output in the IC. The remaining pins are two clock pins, one for each flip flop, one voltage supply pin, one ground pin, and two clear pins for both the flip flops. Commercially available dual D flip flop IC are MC74HC74A, MC74HCT74A, CD4013B, SN54ALS874B, SN74ALS874B, HEF4013, 74LS74, 74AHC74D etc. These Dual D flip flop ICs are used in different applications such as time delay circuits, shift register applications, Building Automation, Power Deliver, Telecom Infrastructure, Test and Measurement, etc.

D flip flop Pin Configuration

CLK1, CLK2 -> clock pulse input

VDD -> Voltage supply

GND -> Ground

D1, D2 -> Data input

C1, C2 -> Clear

S1, S2 -> Set

Q2, Q1 -> output

Q’1, Q’2-> complementary output of the flip flop

Dual D flip flop 7474|Dual D type Positive Edge Triggered flip flop

7474 D flip flop IC has two independent D flip flops: positive edge trigger flip flops; the data input is propagated to output Q with the positive-going edge clock pulse. Setup time and hold time of the D flip-flop should be considered for correct operation. Reset and Set in this IC are asynchronous, i.e., both change the output value at any instant of time without considering the clock pulse. The IC 7474 has a wide operating range because of its large voltage range operation.

D flip flop 7474 Pin Diagram

D flip flop IC 7474 Theory

D flip flop IC 7474 is a TTL device. It has data and clock inputs; these inputs are called synchronous because they operate in step with the clock pulse, whereas preset and reset are the asynchronous input. They are independent of the clock pulse. The preset here is active low, where preset is activated with a low input to its pin, it sets the flip flop output Q as 1. The clear signal is also active low; when the clear input is activated, the output Q of the D flip-flop is set to Zero. 7474 D flip flop IC applications are used for Latching devices, Shift Registers, Buffer Circuits, Sampling Circuits, and Memory and Control Registers.

D flip flop IC 7474 Pin Configuration

Pin Number	Pin Description	Input/Output Pin
1	Clear 1	Input
2	Data 1	Input
3	Clock 1	Input
4	Preset 1	Input
5	Q 1	Output
6	Q’1	Output
7	Ground	Output
8	Q’2	Output
9	Q 2	Output
10	Preset 2	Output
11	Clock 2	Input
12	Data 2	Input
13	Clear 2	Input
14	Voltage supply	Input

7474 D flip flop Circuit

D flip flop IC 74LS74

74LS74 D flip flop IC has 2 d flip flops; here, every flip flop has different input and output pins; it also has Qbar as an output pin; both flip flops are independent of each other. The Flip Flop here has a positive edge-triggered flip flop with a set preset and clear. 74LVC2G80, HEF40312B are equivalent IC of 74LS74.

Negative Edge Triggered D flip flop IC 

SN74HCS72-Q1 D flip flop IC contains a Dual D type negative edge D flip flop, it has an active-low preset and clear pin, and both are asynchronous. It has 14 pins, one voltage source, two clear, two preset, 2 Q output, 2 Qbar output, one ground, two clocks, 2 data input. Both flip-flops are independent of each other. It is used to toggle switches and can operate in noisy environments. 

74HC74 Dual D Type flip flop

74HC74 D flip flop IC contains dual positive edge-triggered D flip flops and has a total of 14 pins. Two asynchronous reset pins, which are active low, 2 data pins, two clock pins, one ground, two outputs, two complementary outputs, two asynchronous set pins which are active low and one voltage source pin. So it is very high immunity to noise.

74LS74 Dual Positive Edge Triggered D flip flops

74LS74 D flip-flop IC (Integrated Circuit) contains two individualistic positive edge-triggered D flip-flops with asynchronous preset and reset pin. It has 14 pins, two asynchronous reset pic, active low, 2 data pins, two clock pins, one ground, two outputs, two complementary outputs, two asynchronous set pins, and one voltage source pin.

CD4013 Dual D flip flop

The CD4013 or 4013 D flip flop IC is an Integrated circuit containing two d flip-flops; in this IC, you can use 3V to 15V. Some also support up to 20V of power supply. There is a different pin for Data input, Set, Reset, Clock, for both the d flip flop in this IC. And as output, also get Q and Qbar for both the flip flops.

Low Power D flip flop

A D flip flop that consumes low power for operation can be designed with AVL (Adoptive voltage level) techniques, TSPC (True single-phase clock) method, or D flip flop designed with transmission gates, which is based on SPTL (Static pass transistor logic) method.

Scan D flip flop

This flip flop has functioned as a simple D flip flop. In addition to that, it has a design for testability. It has scan enable, clock, scan input, and data are the input to a scan d flip flop, enable pin of the flip flop is for it to work as a simple d flip flop or as a scan flip flop. A scan D flip flop is a D flip flop with a multiplexer added to the input where one input of the multiplexer acts as the input data (D) to the D flip flop. This means scan D flip flop is a D flip flop with alternative input sources as per requirement.

TSPC D flip flop

A true single-phase clock d flip flop is a dynamic flip flop type that can perform D flip flop operation with very high speed while using low power, and it also consumes less area. The TSPC method of creating a D flip flop causes minor phase noise in the circuit, which helps to eliminate clock skew.

FAQ/ Short Note

What is the difference between a ring counter and Johnson counter?

Ring counter and Johnson counter are both synchronous counters, there is not much difference between the cirucity of both, here the basic difference between both the counter.

What is the difference between a ring counter and ripple counter?

The ring counter is a synchronous counter, whereas the ripple counter is an asynchronous counter. The difference between both the counters is given below points.

Which counter is faster?

The counter can be of the asynchronous or synchronous counter type. In the synchronous counter, every flip flop receives clock pulse simultaneously, whereas asynchronous counter, every flip flop receives clock pulse at a different time.

The synchronous counter is faster, as all the flip-flops in this counter operate simultaneously. Whereas the speed of the counter depends on the circuitry, type of the flip flop used, clock pulse, delays, etc.

What are the types of shift registers?

The classification of the shift registers into four basic types:

Which shift register is fastest?

There are four different types of shift registers such as SISO, SIPO, PISO, and PIPO. After comparison between all of them, we found out that.

Parallel in and parallel out (PIPO) is the fastest shift register. Here, all inputs and outputs are in parallel form, and the slowest one is the Serial in Serial out (SISO), where all input and output are in sequential format.

What is a mod 8 counter?

Mod is the modulus of the counter which can be number of counter states while counting from minimum to maximum.

Mod 8 counter is a 3 bit counter with 8 states, so it is called mod eight counter. 8 number of input pulses are required to reset this counter to its initial state zero.

What are the application of shift register?

There are several applications for the shift register. Here are some applications for shift register:

Content: Analog Instruments

What is Analog Instruments ?

Analog Electronic Instruments

An analog instrument is one whose output or display is a continuous-time function. This instrument converts the input quantity into an analog O/Ps; having an infinite number of value. An analog instrument typically contains a pointer and a scaled calibrated dialler to show the output.

Selecting factor of Analog Instrument:

Types of Analog Instruments

The analog instrument can also be of two types:

The direct measuring instrument is the instrument that converts the energy of the measuring quantity directly into energy that trigger the instrument, and the magnitude of quantity to be measured instantly.

A comparison instrument that compares the unknown quantity with a standard, when high accuracy is needed, is used.

One more classification of the analog instrument is

Analog Indicating Instruments

It is indicating instrument that show the instantaneous value of the magnitude of the quantity to be calculated. The indicating instrument typically includes all null types of instrument and most passive ones. The most used is a dial and a pointer indication by the pointer moving over a calibrated dial.

The analog indicating instrument can be divided into two groups electromechanical instrument and electronic instrument.

Examples are ammeter and voltmeter.

Recording Instruments

The recording instrument gives a continuous record of the variation of the quantity being measured over a specific period. Although it is used to provide the overall performance of any instrument, it can provide data to evaluate the calibre and efficiency of the operating crews.

Types of Recording Instruments

 Analog Recording Instruments can be of three types:

What is Graphic recording instruments ?

Graphic recording instruments display and store records of the history of some physical event with pen and ink. They even may be varying voltage, current, pressure, etc. It mainly consists of a chart for storing and displaying recorded data. This stylus moves on paper with proper relationship and an internal connection which connects the stylus to the information source.

Integrating Instruments

An integrating instrument is an instrument to find the sum of measurements over a specific period the summation in which this provide as product of time and the measured quantity.

Principle of Operation of Analog Instruments

Operating Torques in Analogue Instruments are

Operating force or torque:

Deflecting Force or torque: It is a force or torque which reflects the pointer from its 0^th position of calibrated scale according to the magnitude of the quantity passing thru the device.

Controlling Force or torque:  which control the movement of the pointer on a required scale. It is needed to bring the pointer to the 0^th point at if no deflecting force. To produce an equal and opposite force to the deflecting Force to make the pointer steady in the absence of controlling Force pointer may swing away from the final study position for any magnitude. Controlling torque can be produced by Spring control gravity control.

Damping force or Torque: This used to prevent from the vibration for oscillation of the pointer on a particular range of scale; It is required to bring back the pointer at rest. Damping force can be established by air friction fluid friction Eddy current damping.

Magnetic Effect

In a uniform magnetic field, a current-carrying conductor is situated, which result in a disturbance in the magnetic field, impacts force (F). The direction of Force will be the opposite direction of the current and coil conductor generate magnetic field act as magnetic material.

Force of attraction or repulsion 

When a piece of soft iron that is not magnetized previously, kept near the end of the coil. When current flow through the coil, the soft iron becomes magnetised and gets pulled inside the coil. The Force of attraction is proportional to the field strength inside the coil and proportional to the current strength; utilized in attractive moving iron (M.I) instrument.

If two soft iron pieces are situated near the coil, become magnetized, and then there will be repulsion force; utilized in repulsive moving iron (M.I) instrument.

The Force between a current-carrying coil and a permanent magnet is used in a permanent magnet moving coil instrument, and Force among 2 current-carrying coil is utilized as the key principle in dynamo meter type of instrument.

Thermal Effect

The current to be measured is passed through a heating element whose temperature increases with the increase in current and temp change is converted into an EMF by a Thermo-couple. The thermocouple is designed with two dissimilar electric conductors joined together at the end of each other to form a close loop, the point the dissimilar metal meets is the junction. If both the junction is maintained at a different temperature, a current will flow through the loop.

Electrostatic Effect

The electrostatic effect is the attractive force among 2 or many electrically charged elements between which a potential diff is preserved. That force results in to increase in deflecting torque. The electrostatic effect is the basic principle of an electrostatic instrument known as an electrometer voltmeter, an example of an electrostatic instrument.

Advantages of electrostatic instrument:

Disadvantages of electrostatic instruments:

Induction Effect

Induction effect when a non-magnetic conducting disc or drum is placed in the magnetic field which is excited by alternating currents, EMF will be induced in the drum or disc. If the closed path is provided, then EMF will cause a current flow to the drum or disc. the produced force in the interaction of the induced current and the magnetic field will cause the disc or drum to move this effect is used in energy meter.

Advantages of induction instruments:

Disadvantages of induction instrument:

Errors in the induction instrument are due to frequency variation or temperature variation.

Hall Effect

This is the formation of potential difference across a conducting material having electrical current exist in a cross magnetic field.

The magnitude of the potential drop depends on the current flux density, and the internal property of the conductor is called the hall effect coefficient. The emf produced in this phenomenon is so small for measurement, which may require amplification. Hall effect instruments are used for sensing current or in magnetic measurement. Examples are flux meter ammeter Poynting vector watt-meter. Hall effect instruments convert the magnetic field into electric quantity, which can be easily be measured.

Advantages of hall effects:

Disadvantages of hall effects:

What are the advantages of digital instruments over analog instruments?

Advantages and Disadvantages of Analog and Digital Instruments.

Advantages of Digital Instruments over Analog :

Disadvantages of Digital Instrumentation:

Advantages of Analog Instrumentation:

Disadvantages of Analog Instrumentation:

Analog Devices Instrumentation Amplifier

Analog devices instrumentation amplifier when the output of any instrument is low or needed any amplification for further processing the input to the instrument amplifier is the output from the centre of the transducer used to amplify, reject noise and signal interference. An instrumentation amplifier is a differential amplifier, and an analog device instrumentation amplifier is a precision block with a differential input and output. This device amplifies the differences between the two input signal voltages while rejecting signals common to both inputs.

Analog Instrument Cluster |Instrument Cluster Analog

An analog instrument cluster is a group of different analog instruments, and it can include different analog metres and gauges to provide the required measurement. These clusters are used for safety order requirement mainly used in automobiles, aircraft etc. this cluster use different m for measuring required information, for example, in automobile, speed, fuel level, charge level, etc.

What is the difference between Digital and Analog Measuring Instruments ?

Comparison between Analog and Digital instruments

Analog Instrument	Digital Instrument
Low Precision	High Precision
High power Requirement	Low Power Requirement
Highly Sensitive	Less Sensitive
Cheap	Expensive
Less Resolution	High Resolution
Not compatible directly with a computer, microprocessor or microcontroller	compatible directly with a computer, microprocessor or microcontroller
More Flexible	Limited flexibility
Parallax error during reading result is possible	No reading error due to digital display
Can get easily affected by noise	High noise immune
Easily portable	Not easily portable
Continuous convenient for readout	Convenience in readout

Electronic Test Instruments Analog and Digital Measurements

Electronic test instrument testing instruments are used to detect a fault in operation, such as voltmeter, ammeter, ohmmeter, multimeter, frequency counter, oscilloscope or LCR meter, etc.

The testing instrument is the key to any electronic design production and maintenance. It can be an analog or digital instrument used to generate a signal and capture the response from the device Under test.

Analog Aircraft Instruments

Following are the analog instruments which are used in aircraft:

The altimeter is a device used to measure an object’s altitude relative to a fixed level. It has two types of pressure altimeter and radio altimeter and study of altitude is known as altimetry. 

A pressure altimeter calculate altitude as per atmospheric pressure. With the increase in altitude, the pressure reduces. Radio altimeter determines the height of any subject by sending a signal to the ground and measure the attitude based on the time required for the radio wave signal to travel. Altimeter having mechanical internal aneroid capsule have an analog display.

Air speed indicator is used to measure the aircraft’s speed; It uses a pitot tube which is U shaped with two openings .airspeed indicator traditionally is a mechanical analog instrument.

Magnetic compass and instrument for determining direction by using a magnetic element which shows the direction of the horizontal component of the magnetic field of the earth

The tachometer is a device that indicates the rate of rotating an object or engine shaft; it includes the instantaneous value of speed in RPM. It is composed of a tile and little to indicate the immediate reading.

Analog Polygraph Instrument

An analog polygraph instrument is commonly known as the Lie Detector instrument, measuring at least three physiological responses like blood pressure, pulse respiration, and skin connectivity.

It can consist of pneumographs to record respiratory activity, blood pressure cliff to record cardiovascular activity,  and galvanometer activity sensor, plethysmograph, etc. The analog polygraph needles draw the line on a paper to record and show the output. These lines represent the level of stress which can affect if the person is telling a lie.

Analog Weather Station Instruments

Analog weather instruments:

The thermometer is used to measure the temperature of the environment. There are many types of thermometers. One of the most used thermometers is a thermistor designed with metal oxide and has a high-temperature Coefficient, so with the temperature change, the resistance shift occurs.

Thermistor mainly has negative temperature Coefficient. Although the increase in temperature resistance decreases, it is very sensitive to temperature change, making thermistors useful for Precision temperature measurement.

A barometer is an instrument uses to measure the pressure of the atmosphere because atmospheric pressure varies with altitude. A simple barometer is a mercury-in-glass barometer unit of measurement. The atmosphere or bar Mercury glass parameter is closed at the top and open at the bottom. Thus, there is a pool of Mercury. 

The aneroid barometer is a non-liquid barometer that is widely in use. It is small and uses an evacuated capsule as a sensing element, the flexible walled evacuated capsule. The flex with the change in atmospheric pressure the deflection is coupled mechanically to an indicating needle.

A hygrometer is a device that indirectly measures humidity by sensing a change in physical or electrical property in materials, which causes due to moisture content. There are different types of hygrometers for humidity measurement. In mechanical hygrometer measures humidity with the change in length of the hair element by the contraction and expansion of the hair element. 

A rain gauge is a device that is used to measure rain in a certain period. It usually measured rainfall in millimetres. There are different types of rain gauges. The most precise one is the ground level gauge, where the orifice of the gauge is placed with the ground level surface and surrounded by an anti-splash grid.

Anemometer is a device that measures the rate of flow, which can be used for measuring airflow. A hot wire anemometer is widely used for measuring the mean and fluctuating velocity of fluid flows. Steam of air will cool down a heated object is the principle of hot wire anemometer a heated wire is placed in the airflow.

Pyranometer is an instrument that is used to measure solar radiation. It is operated on the measurement of the temperature difference between a bright surface and a dark surface. There are different types of pyranometers, such as thermopile pyranometers, photovoltaic pyranometers, etc.

Examples of Analog Instruments

Uncertainty for Analog Instruments

Uncertainty of analogue resolution uncertainty is one of the problems in analogue instruments. It considers the limitation of measurement. The Precision accuracy of a measurement is limited by the resolution of the instrument for an analog instrument with gradual scaling sometimes causes parallax error when taking a reading from different view position will give different reading leads to an error which creates uncertainty in measurement.

Frequently Asked Questions.

What are absolute and secondary instruments?

Absolute Instrument:

These instrument provides the magnitude of the measuring quantity in terms of physical instrumental constant. 

Secondary instrument:

These instrument convert the analog o/ps  of the primary/absolute instrument into an electrical signal. These instruments are required to be calibrated by comparison with an absolute instrument that has already been calibrated.

Analog Instruments are preferred for ?

Error in Analog Instruments ?

three different types of error that happen in any instrument:

•  Instrumental Errors: These errors are caused by miss-use of the instrument, loading effect, ageing or inherent shortcomings.
•  Environmental Errors: These errors are caused by external condition of the instrument, hence errors are may affect by surroundings temp, pressure, humidity, dust, etc.
•  Observational Errors: these errors occur due to human observational factors. There can be reading parallax error in analog instruments, which is an observational error. Different moving parts in an analog instrument can produce an error when friction between two components is created, an instrumental error. Ageing of the instrument can produce an error is also an instrumental error. 

What are some examples of common Analog Devices ?

What are the Comparative Advantages and Disadvantages of Digital and Analogue Multimeters ?

What is a Micrometer ?

Micrometer is also known as micrometer caliper or micrometer screw gauge. It is an instrument for measuring linear(small) distance precisely, such as diameter, length, thickness, etc. 

How does an Ohm Meter Measure Resistance ?

Ohm meter can not measure resistance directly but can measure the power through a circuit. Any known voltage is connected to a component whose resistance is measured, where resistance is unknown by measuring the current through the measuring component. Through Ohm’s Law relationship between voltage current and resistance is known. Therefore, we can calculate the value of the unknown resistance by finding current through the circuit as the voltage is known.

Is Wifi a Digital Signal or an Analog?

The wifi signal is both analog and digital and for that ,  ADC  and DAC and modulation of the signal takes place as requirements.

What is Wattmeter and its construction?

A wattmeter is an instrument that measures the electrical energy of a circuit. The unit of measurement is in watts. It can be an electro-dynamometer or induction watt meter. It can be constructed with a current coil and voltage coil, the current coil is adjoining in series connection, and the voltage coil is connected by parallel connection. The needle which moves on the calibrated scale is connected to the voltage coil. The voltage coil is a moving coil, whereas the current coil is immobile.

How to find Multiplication factor for Wattmeter ?

Multiplication factor = (voltage range X current range X power factor)/(range of wattmeter)

Is there anything that an Analog Multimeter does better than Digital one If so Why ?

Analog multimeters are suitable for measuring fluctuating values better than that of digital multimeters, because sudden fluctuation can not be precisely represented by digital multimeters. While analog multimeter has changing display which can accurately show the sudden fluctuations, it may not provide exact reading but it will provide instantaneous and rough measurement.

What are the different types of a flip flop?

D flip flop Types

• Synchronous D type flip flop.
• Asynchronous D type flip flop.
• Level Triggered D type flip flop.
• Edge triggered D type flip flop.

Level triggered D flip flop

D flip-flop whose output changes according to the input with a high level of the clock pulse is a level triggered D flip-flop, and then the clock level is low, the D flip-flop stays in a hold state.

What is Edge Triggered D type flip flop ?

D type Edge Triggered flip flop

D edge triggered flip-flop is the flip-flop in which the output can change only with the edge of the clock pulse, regardless of the change in the input. That means the output of the flip-flop changes with the transition of the clock pulse, either from high to low to high. 

D type Edge Triggered flip flop type

Edge triggered D type flip flop can be of 2- types:

The edge triggered flip Flop is also called dynamic triggering flip flop.

Edge Triggered D flip flop with Preset and Clear

Edge Triggered D type flip flop can come with Preset and Clear; preset and Clear both are different inputs to the Flip Flop; both can be synchronous or asynchronous. Synchronous Preset or Clear means that the change caused by this single to the output can affect the clock pulse; here, it is edge triggered to change with the edge of the clock pulse. Whereas Asynchronous Preset can Clear can change the output at any instant of time.

Edge Triggered D flip flop Timing Diagram

The given timing diagram shows one positive type of edge triggered d flip flop; there is clock pulse CLK, D the input to the D flip flop, Q the output of the D flip flop; as you can see, the changes in output are happening during the transition of the clock pulse from low to high, because it is a timing diagram of a positive edged D type flip flop.

Edge Triggered D flip flop Circuit Diagram

The circuit diagram of the edge triggered D type flip flop explained here. First, the D flip-flop is connected to an edge detector circuit, which will detect the negative edge or positive edge of the clock pulse. Then, according to the output of the edge detector circuit, the D flip flop will operate accordingly.

Edge Triggered D flip flop Truth Table

Rising Edge Triggered D flip flop | Positive Edge D flip flop

The positive edge D type flip flop, which changes its O/P according to the I/P with the +ve transition of the clock pulse of the flip flop, is a positive edge triggered flip-flop. It has high-speed performance with low power consumption, that is because it is widely in use. The positive edge D type flip flop can be represented with a triangle at the D flip-flop block diagram at the clock end. 

Positive Edge Triggered D flip flop Circuit Diagram

The Positive edge triggered D type flip flop circuit can be designed with three latches, where two input latches are adjoining with the clock pulse, one latch is attached with the input data, the circuit is designed in such a way that the output response happens only at positive transition of the clock pulse.

Positive Edge Triggered D flip flop Timing Diagram

Clock pulse CLK, D the input to the D flip flop, Q the output of the D flip-flop, the changes in output is happening during the transition of the clock pulse from low to high.

Positive Edge Triggered D flip flop Truth Table

Falling edge Triggered D flip flop | Negative Edge Triggered D flip flop

The D flip-flop, which changes its output according to the input with the -ve. transition of the clock pulse of the flip-flop, is a -ve. edge triggered flip-flop. The negative edge D flip-flop can be represented with a triangle and a bubble at the clock end of the D flip-flop block diagram.

Negative Edge Triggered D flip flop Circuit Diagram

The -ve edge D flip flop can be designed by adding a -ve edge detector circuit with the clock pulse. The -ve edge detector detects the -ve edge of the clock pulse. According to the O/P of the detector circuit, the rest of the circuit will operate. When there is a negative transition in the clock pulse, the circuit produces output according to the input. Otherwise, the circuit stays in a hold state.

Negative Edge Triggered D flip flop Timing Diagram

Clock pulse CLK, D the input to the D flip flop, Q the output of the D flip flop, the changes in output is happening during the transition of the clock pulse from high to low; this is the characteristic of the negative edge flip flop.

Negative Edge Triggered D flip flop Truth Table

Master Slave D flip flop | MS D flip flop

Master Slave flip-flop was designed to make synchronization more predictable. To avoid race around conditions, a master slave flip-flop is also known as the pulse-triggered flip Flop because the response time of the output is equal to the width of the one clock pulse.

  Master slave D flip flop can be configured from 2-D flip-flop; each flip-flop is connected to a CLK pulse complementary to each other. One flip-flop as Master and the other act as a slave; when the clock pulse is high, Master operates and slave stays in the hold state, whereas when the clock pulse is low, the slave operates and the Master stays in a hold state. The O/P of the Master is feed into the slave flip-flop as I/P.

How to design Master Slave D flip flop using NAND gates ?

Master Slave D flip flop Circuit Diagram

The master slave D flip flop is designed with NAND gates, configured with 2-D flip-flops, one a latch with the gated circuit, as a master flip-flop, and the other work as a slave flip-flop with a complemented CLK pulse to each other.

Master Slave D flip flop Truth Table

D	Q(PREVIOUS)	CLOCK	Q
0	0	1	0
0	1	1	0
1	0	1	1
1	1	1	1
0	0	0	0
0	1	0	1
1	0	0	0
1	1	0	1

Timing Diagram of Master Slave D flip flop

In the given diagram, a signal of the CLK pulse, D the I/P to the master flip-flop, Qm is the O/P of the master flip-flop, and Q is the O/P of the slave flip flop. Thus, the behavior of a master slave D flip-flop can be observed through its timing-diagram.

Master Slave Edge Triggered D flip flop

If the master slave circuit is designed with edge triggered D flip flop, or in addition to D flip-flop circuit, there is one edge detector circuit, which detects the edge of a clock pulse. According to the output of the detector, the Flip-flop works. Then the overall circuit is a master slave edge triggered flip flop circuit.

D flip flop Design

D flip flop can be configured in many ways, like it can be created with NAND gate, NOR gate, Multiplexer, etc. It can be derived from other flip flops like JK flip flop, SR flip flop, or T flip flop. It can be designed with the help of many different combinations of the circuit with the clock.

How to design D flip flop using NAND gate ?

D flip flop circuit diagram using NAND gates

The D flip flop can be designed with NAND gate only, here one SR latch is designed with NAND is gated with two more NAND gates, and the clock pulse is input to the gated NAND with Data input, where one NAND gate D as input and the other NAND gate gets D compliment as one input. And according to the gated output, the SR latch is processed. The resulting circuit is a D flip flop circuit.

How to design D flip flop using NOR gate ?

D flip flop using NOR gate

The D flip flop can also be designed with NOR gates; here, three SR latches with clock pulse are used to develop the D flip-flop. The two input SR latch create the D and D complement output separately, and that output is feed into the third latch, which produces Q and Q-compliment as output. 

When there is no clock pulse, the initial latches get locked with the current state because of the interconnections, which cause the whole flip Flop to put on a hold state; regardless of the change in input data, the output cannot change.

D flip flop using 2 D Latches

Transparent latch D flip flop

What is D flip flop SR Latch circuit diagram ?

How to design D flip flop Using CMOS ?

D flip flop using CMOS Transistors

 

Design D flip flop using Transmission Gate

The D flip flop can be designed with a Transmission gate, which reduces the complexity of the circuit as it reduces the number of transistor counts. When LOAD =0, the Latch stores the data input; when LOAD = 1, the latch is transparent. The transmission gate also helps to reduce the overall circuit size.

CMOS D flip flop Schematic

D flip flop using 2×1 MUX

D flip flop using MUX Explanation

A D flip flop can be designed with a single multiplexer(MUX), data ‘D’ is an input to the MUX, and the other input of the MUX is the feedback of the multiplexer output Q to itself’s input, the clock signal is acting as select line, If the clock (CLK) = one then the output of the MUX is D, otherwise the output of the MUX remain the past output Q. 

How to Design D flip flop using JK flip flop ?

Conversion of JK flip flop to D flip flop

D will be the external input to the JK flip flop, and JK flip flop is the universal flip Flop; we can design D flip-flop from the JK flip flop if we connect the K input of the JK flip flop with an inverter to the J input. Then the resulting circuit will be D flip-flop with I/P as D and O/P as Q and Qbar.

Inputoutput JK flip inputflop DQnQn+1JK0000X010X11011X111X0 Table: Conversion table from Jk flip flop to D flip flop with input and output values.

Where Qn+1 means the next output state and Qn means the present output state in the conversion table.

How to design Frequency Divider Circuit using D flip flop ?

D type flip flop Frequency Divider | D flip flop Clock Divider

A frequency divider is a digital circuit that divides an input frequency by a required factor. One such frequency divider is designed with a D flip flop, which divides the input clock frequency by two. One inverted feedback is from output Q to the input D is forming this frequency divider circuit.

Divide by 3 Circuit using D flip flop

The given circuit divides the input frequency by three. In this circuit there is 2 D flip-flop is used, and one NOR gate, which forms the resulting circuit, divides the input frequency by three.

Phase Detector using D flip flop

A phase frequency detector is a circuit used to detect the difference of frequencies and phase of two given inputs. The UP signal is generated when the clock signal is slower than the reference clock signals. The down signal is generated when the clock signal is faster than the reference clock.

The phase frequency detector can be designed with two D flip-flop as shown in the above figure; both the flip flop has different clock frequencies as input, and the reset of the flip flops are connected with a NAND gate whose input is the Down and Up signal.

Frequency Multiplier using D flip flop

The frequency multiplier is a digital circuit that generated the multiple of the input clock frequency signal. 

The circuit can be designed with the D flip-flop and even the number of inverted in the feedback line. The feedback is started from the output Q and goes to the NOR gate, which is attached with the clock input of the Flip Flop. The multiplier circuit output depends on the delay produced by the inverters; with different delays, we can produce different frequencies as output.

D flip flop Oscillator

The oscillator is a circuit that generates repeated and alternating waveforms. The oscillator can be designed with D flip-flop, where D flip-flop must be in a toggle, so whenever it gets a high input, the output value should toggle; for creating toggle flip flop from d flip flop, the complementary output of the D flip-flop is feedback to the Data input of the D flip-flop.

D flip flop Register

A register is a group of flip flops that can store more than one bit at a time, depending on the number of flip flops in the register.

What are the Quad D flip flop IC ?

Quad D type flip flop 74175 | Quad D flip flop 7475

Quad d flip flop is available in Ingratiated circuitry, which has 16 pins. It has a 4 d flip flop with separate input(D) and output ( Q and Qbar ) pins. The remaining pins are one ground, one clear, one clock, and one voltage supply pin. Its function is equivalent to the TTL 74175. It contains edge triggered D flip flop.

Hex D type flip flop

It is a type of d flip flop available in IC, which contains 6 d flip flops each has different input and output pin in the integrated circuit. Thus, it has 16 pins with one clock pin, one ground pin, one voltage supply pin, and one clear pin.

8 bit Octal D flip flop

Octal d type flip flop is commercially available as an Ingratiated circuit. It contains 20 pins, which have three-state output. All the flip-flops are mainly controllable by the clock and enable pin. Each flip Flop has different input (D) and output (Q) pins. The remaining pins are one clock pin, one ground pin, one voltage supply pin, one clear pin. This Ic is used to design a storage register, pattern generator, etc.

16 bit D flip flop

 It is a type of D flip flop available in IC; mainly a 16-bit edge triggered d flip flop with three-state output, designed for driving highly capacitive or low impedance load. It can be used as a 16 bit flip Flop, also can be used as two 8 bit flip flops. It has 48 pins, whereas each flip Flop has separate pins for input and output; two clock pins and two enable pins. It is used in designing buffer registers, input or output ports, bidirectional buses, etc.

 Content :

Verilog was originally for stimulation and verification of digital circuits, it is a hardware description language (HDL). Here, all the code is designed with D flip flop whether VHDL or Verilog code.

Verilog Code for D flip flop using NAND gates

module nand_g(c, a, b); //*each module contains statements that defines the circuit, this module defies a NAND gate which is named as nand_g*//

input a, b; / a and b is the input variable to the NAND gate
output c; / output variable of NAND gate is defined
assign c = ~(a & b); / this assign is used to derive the value of c through a and b
endmodule /module end with endmodule statement

module not_g(e, f); / this block defines the NOT gate
input f; / f is the input variable to the NOT gate
output e; / e is the output variable of the NOT gate
assign e = ~f;
endmodule

module d_ff_st(q_out, qbar_out, d_in, clk_in );
 //* this module defines a d flip flop which will be design with NAND gate and NOT gate *//
input d_in, clk_in; / input variable of D flip flop d_in is the data input and clk_in is the clock input 
output q_out, qbar_out; / output of the D flip flop q_out and qbar_out where q_out and qbar_out is compliment to each other

not_g  not_1(dbar, d_in); /NOT gate module is called with dbar and d_in parameter

nand_g nand_1(x, clk_in, d_in); /NAND gate module is called with x, clk_in and d_in parameter
nand_g nand_2(y, clk_in, dbar); /NAND gate module is called with y, clk_in and dbar parameter
nand_g nand_3(q_out, qbar_out, y); / NAND gate module is called
nand_g nand_4(qbar_out, q_out, x); / NAND agte module is called
endmodule

Verilog Code for D flip flop with Asynchronous Reset

module dflip_flop_asy_rst (q, d_in, clk_in, reset_in);

input d_in, clk_in, reset_in; / input variables  of the d flip flop is defined
output reg q; / output variable of the d flip flop is defined
always@ (posedge clk_in or posedge reset_in) 

//* always block is the block who's statements are executed sequentially here the block will executed when clk_in is in positive edge or reset_in is in positive edge *//

if (reset_in) / if reset_in is high or true then q <= 1'b0 
q <= 1’b0; / here 1'b0 means one bit number value zero
else / if reset_in is low or false then q<= d_in
q<=d_in;
endmodule / end of the module

Verilog Code for D flip flop using Dataflow Modelling

//* 
Dataflow modeling provides the descriptions of combinational circuits by their function rather
than by their gate structure.*//

module dflipflo (q, d_in, clk_in); / module defines d flip flop in data flow modelling

input clk_in, d_in ; / input variable of the d flip flop

output q; / output variable of the d flip flop

assign q = clk_in ? d_in : q; / if clk_in is true the q = d_in and if clk_in is flase the q = q

endmodule

D flip flop Behavioral Verilog Code

//* Behavional is used when cicruit is sequential circuit it contain procedural statements *//
module dflip_flop_bh (q, d_in, clk_in); 

input d_in, clk_in; / input variable of d flip flop is defined
output reg q; / output variable of the d flip flop is defined

always @ (posedge clk_in) / the block is takes place continuously when clk_in is in its positive edge of the pulse

if(clk_in) / if clk_in is high or true then q<=d_in
q<=d_in;
endmodule

Verilog Code for Shift Register using D flip flop

//* this code is used to designed 4 bit shift register using d flip flop, here left to right shifting is taking place through this code*//
module shift_reg_LtoR (out, clock, reset_in, in);/ this module define left to right shift register of 4 bit

input in, clock, reset_in; / input variable is defined
output out;
output reg [3:0] s; / output varible s is defined as a register that can have 4 bit value

always@ (posedge clock, negedge reset_in) 
//* the sensitivity of this block is negative edge of reset_in or positive edge of clock *//
\t
if(!reset_in) / if else statement
s<=4’d0;
else
s<={ s [ 2 :0], in}; //* as s can have 4 bit value the s[2 : 0] has 3 bit and in has 1 bit, together they produce the 4 bit of s *// 
assign out= s[3];
endmodule

4 bit Ripple Counter using D flip flop Verilog Code

//* following code is for 4 bit ripple counter designed with d flip flop*//
module dff_r (input d_in, clk_in, rst_in, output reg q, output q_n); 
//* module define a d flip flop with clock, reset, d, as input, and q and qbar as output *// 

always@(posedge clk_in or negedge rst_in) //* this block sensitivity is positive edge of clk_in pulse or negative edge of rst_in *// 

if (! rst_in) / if rst_in is low or false the q is implemented with zero
q<=0;
else
q<= d_in;
assign 
 q_n <= ~q;
endmodule

module ripple_c (input clk_in, rst_in, output [3:0] o); / this module define the ripple counter of 4 bit
wire q_0, qn_0, q_1, qn_1, q_2, qn_2, q_3, qn_3; / wire is used to define the output or input signal 

 //* implementing d flip flop module with different parameter 4 times *//
dff_r dff_0(.d_in(qn_0), .clik_in(clk_in), .rst_in(rst_in), .q(q_0), .q_n(qn_0));
dff_r dff_1(.d_in(qn_1), .clik_in(q_0), .rst_in(rst_in), .q(q_1), .q_n(qn_1));
dff_r dff_2(.d_in(qn_2), .clik_in(q_1), .rst_in(rst_in), .q(q_2), .q_n(qn_2));
dff_r dff_3(.d_in(qn_3), .clik_in(q_2), .rst_in(rst_in), .q(q_3), .q_n(qn_3));

assign o={qn_0, qn_1, qn_2, qn_3};

endmodule

Positive Edge Triggered D flip flop Verilog Code

module pos_edge_df (q, d_in, clk_in, rst_in);
 //* this module define d flip flop with q as output and data, clock and reset as input *//

input d_in, clk_in, rst_in; / input variable of the d flip flop is defined
output reg q; / output variable of the d flip flop is defined

always @ (posedge clk_in) / this block is implemented continuously with every positive edge of the clock pulse

if ( !rst_in) / if else statement
q<= 1’b0;
else
q<=d_in;

endmodule

Negative Edge Triggered D flip flop Verilog Code

module pos_edge_df (q, d_in, clk_in, rst_in);  
//* this module define d flip flop with q as output and data, clock and reset as input *//

input d_in, clk_in, rst_in; / input variable of the d flip flop is defined
output reg q; / output variable of the d flip flop is defined

always @ (negedge clk_in) / this block is implemented continuously with every negative edge of the clock pulse

if ( !rst_in) / if else statement
q<= 1’b0;
else
q<=d_in;

endmodule

Verilog Code for D flip flop using Structural Model

/Structural model is used to integrate diffrenet blocks

module nand_gat(co, a, b); / this module defines NAND gate
input a, b; 
output co; 
assign co = ~( a & b); 
endmodule

module not_gat(e, f); / this module defines NOT gate
input f; 
output e; 
assign e= ~f; 
endmodule

module d_ff_strt(q,q_bar,d_in,clk_in); //* this module define d flip flop with q and qbar as output, and data and clock as input *//
input d_in, clk_in; / input variable of the d flip flop is defined
output q, q_bar; / output variable of the d flip flop is defined

not_gat not1 (d_bar, d_in); / here NOT gate module is implemented

/ next NAND gate module is implemented with different parameters 4 times
nand_gat nand1 (x, clk_in, d_in); 
nand_gat nand2 (y, clk_in, d_bar); 
nand_gat nand3 (q, q_bar, y); 
nand_gat nand4 (q_bar, q, x); 

endmodule

Verilog Code for Ring Counter using D flip flop

module dffc (q_in, d_in, clk_in); / d flip flop module is defined
output reg q_o;
input d_in,c_in;
initial
q_o=1'b1;

always@(posedge clk_in) / sensitivity is positive edge of the clock pulse
q_o = d_in;
endmodule

module ring_counterdff (q_o, clk_in); / ring counter module is defined with d flip flop
inout [3:0]q_o;
input clk_in;

/ d flip flop module is implemented with different parameters 4 times
dffc df1(q_o[0], q_o[3], clk_in);
dffc df2(q_o[1], q_o[0], clk_in);
dffc df3(q_o[2], q_o[1], clk_in);
dffc df4(q_o[3], q_o[2], clk_in);
endmodule

Verilog Code for T flip flop using D flip flop

module T_ff(q, t_in, clk_in, rst_in); / this module define T flip flop 

input t_in, clk_in, rst_in; / input variable of the t flip flop is defined
output q; / output variable of the t flip flop is defined

always @ (posedge clk_in) / sensitivity of this block is positive edge of the clock pulse
if(rst_in)
t_in<=t_in^q;
endmodule

D flip flop Verilog Code with Testbench

//* following code is the test bench for a d flip flop is does not have any input or the output as variable, it's purposes is of exercising and verifying the functional correctness of the hardware model *//
module d_flipflopt_b;

reg d_in;
reg clk_in;
wire q;

d_flipflop_mod uut (.q(q),.d_in(d_in), .clk_in(clk_in) );
initial begin
d_in = 0;
clk_in = 0;
end

always #3 clk_in=~clk_in;
always #5 d_in=~d_in;
initial                     #100 $stop;

endmodule

Master Slave D flip flop Verilog Code

module M_slave(d_in, reset_in,clk_in, q ,q_bar);/ this module define the master slave of d flip flop
 input d_in, clk_in ,reset_in;
 output q, q_bar; 
 Master Maste_r(d_in, reset_in, clk_in, qn, q_barn); / implementing master d flip flop module 
 Master Slav_e(q_n,reset_in,!clk_in,q, q_bar); / implementing slave d flip flop module
endmodule

module Master(d_in, reset_in, clk_in, q_in, q_bar); / this module defines d flip flop
 input d_in, reset_in, clk_in;
 output reg q, q_bar;
 initial
  q = 0;
 
always @(posedge clk_in) begin
  if (~reset_in) begin
   q <= d_in;
   q_bar <= !d_in;
  end
  
else begin
   q <= 1'bx;
   q_bar <= 1'bx;
 end

 end

endmodule

JK flip flop using D flip flop Verilog Code

module D_flip_flopf (input D_in ,clk_in ,Reset_in, enable_in,  output reg Fo); / this module define D flip flop
    always @(posedge clk_in) begin
        if (Reset_in)
            Fo <= 1'b0;
        else if (enable) 
            Fo <= D_in;
    end 
endmodule

module JK_flip_flopf (input J_in, K_in ,clk_in, Reset_in, enable_in, output Q); / this module defines JK flip flop
    wire S_1,S_2,S_3,S_4,S_5;
    D_flip_flopf D1(S_4, clk_in, Reset_in,enable_in, Q );

    not N2(S_5, Q);
    and A1(S_1, J_in ,S_5);
    not N1(S_3, K_in);
    and A2(S_2,S_3,Q);
    or O1(S_4,S_1,S_2);
endmodule

Frequency Divider using D flip flop Verilog Code

module freq_div_by2 (clk_out, clk_in, reset_in); //* this module defines frequency divider which can devide the frequency by 2 *//
input clk_in, reset_in;
output reg clk_out;
always @ (posedge clk_in)
if(reset_in)
clk_out<=0;
else clk_out<=~clk_out;
endmodule

D flip flop Verilog Code Gate Level

module dffgate(D_in, CLK_in, Q ,Q_n);
    input D_in, CLK_in;
    output Q, Q_n;
    reg Q, Q_n, Ro, So;

always @(negedge CLK_in) begin
    Ro = ~(~(~(D_in|So)|Ro)|CLK_in);
    So = ~(~(D_in|So)|Ro|CLK_in); 
    Q = ~(Ro|Q_n);
    Q_n = ~(So|Q);
end
endmodule

Image Credit : “Binary code” by Christiaan Colen is licensed under CC BY-SA 2.0

VHDL Code for D flip flop

library ieee;
use ieee.std_logic_1164.all;

entity d_flip_flop is 
port (d_in, clk_in: in std_logic; q, q_bar: out std_logic);
end d_flip_flop;

architecture beh_v of d_flip _flop is 
signal qn, q_barn: std_logic;
begin
Process (d_in, clk_in)
begin
If (clk_in’ event and clk_in = ‘1’)
then qn <=d_in;
end if;
End process;
q<=qn;
q_bar<=not (qn);
end beh_v;

VHDL Code for D flip flop using Dataflow Modelling

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity d_flip_flop is 
port (d_in, clk_in: in std_logic; q_in, q_out: inout std_logic);
end d_flip_flop;

architecture data_f of d_flip_flop is
signal d_1, s_1, r_1: std_logic;
begin
s_1 <= d_in nand clk_in;
d_1 <= d_in nand d_in;
r_1 <= d_1 nand clk_in;
q_in <= s_1 nand q_out;
q_out <= r_1 nand q_in;
end data_f;

VHDL Code for D flip flop using Structural Model

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity d_f _f_st is 
port (d_in, clk_in: in std_logic; q_in, q_out: inout std_logic);
end d_f_f_st;

architecture d_ff_s of d_f_f_st is
component nand_1
port (a, b : in std_logic; c : out std_logic);
begin

n_0: nand_1 port map(d_in, clk_in, s_1);
n_1: nand_1 port map(d_in, d_in, d_1);
n_2: nand_1 port map(d_1, clk_in, r_1);
n_3: nand_1 port map(s_1, q_out, q_in);
n_4: nand_1 port map(r_1, q_in, q_out);
end d_ff_s;

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity nand_1 is
port (a, b: in std_logic; c: out std_logic);
end nand_1;

architecture beha_v of nand 1 is 
begin
c<= a nand b;
end beha_v;

D flip flop Behavioral VHDL code

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity d_flip_flop_bh is
port (d_in, clk_in, rst_in: in std_logic; q_in, q_out: out std_logic);
end d_flipflop_bh;

architecture beh_v of d_flip_flop_bh is 
begin
process(d_in, clk_in, rst_in)
begin
If (rst_in = ‘1’) then q_in <= ‘0’;
else if (rising_edge(clk_in)) then q_in <= d_in;
q_out<= not d_in;
end if;
end process;
end beh_v;

VHDL Code for D flip flop with Asynchronous Reset

library ieee;
use ieee.std_logic_1164.all;

entity d_ff_asy_rst is
port (d_in, clk_in, reset_in: in std_logic; q_out: out std_logic);
end d_ff_asy_rst;

architecture beha_v of d_ff_asy_rest is 
begin
if (reset_in = ‘0’) then q_out<=’0’;
elseif (clk_in’ event and clk_in= ‘1’)
then
q_out<=d_in;
end if;
end process;
end beha_v;

VHDL Code for D flip flop with Synchronous Reset

library ieee;
use ieee.std_logic_1164.all;

entity d_syn_reset
port( d_in, reset_in, clk_in: in std_logic; q_out: out std_logic);
end d_syn_reset;

architecture beha_v of d_syn_reset is
begin
process
begin
wait until (clk_in’ event and clk_in =’1’)
if reset_in = ‘0’ then q_out<=’0’;
else
q_out<= d_in;
end if;
end process;
end beha_v;

VHDL Code for Negative Edge Triggered D flip flop

library ieee;
use ieee.std_logic_1164.all;

entity d_ff_neg is
port (d_in, clk_in: in std_logic; q_out: out std_logic);
end d_ff_neg;

architecture beha_v of d_ff_neg is
begin process (clk_in) begin
if (clk_in’ event and clk_in = ‘0’) then
q_out<= d_in;
end if;
end process;
end beha_v; 

Test Bench for D flip flop in VHDL

library ieee;
use ieee.std_logic_1164.all;

entity d_flip_flop_test is
end d_flip_flop_test;

architecture behaviour of d_flip_flop_test is
component d_flip_flop_test
port( d_in: in std_logic; clk_in : in std_logic; rst_in: in std_logic; d_out: out std_logic);
end component;
signal d_in: std_logic:= ‘0’;
signal clk_in : std_logic:= ‘0’;
signal rst_in: std_logic:= ‘1’;
signal d_out: std_logic;
constant clk_p: time:=20ns;
begin 
uut: d_flip_flop_test
port map(d_in=>d_in; clk_in => clk_in; rst_in=> rst_in; d_out=> d_out);
clk_p: process begin
clk_in<=10;
wait for clk_p/2;
clk_in<=’1’;
wait for clk_p/2;
end process;
sti_prc: process
begin
rst_in<=’1’;
wait for 50 ns;
rst_in<= ‘0’;
d_in <= ‘0’;
wait for 50ns;
rst_in<=’0’;
d_in<= ‘1’;
wait;
end process;
end;

4 bit Shift Register using D flip flop VHDL Code

library ieee;
use ieee.std_logic_1164.all;
 
entity p_I_p_o is
 port(
 Clk_in: in std_logic;
 D_in: in std_logic_vector(3 downto 0);
 Q_1: out std_logic_vector(3 downto 0)
 );
end p_I_p_o;

architecture archi of p_I_p_o is
begin
 process (clk)
 begin
 if (CLK_in'event and CLK_in='1') then
 Q_1 <= D_in;
 end if;
 end process;
end archi;

VHDL Code for 8 bit Register using D flip flop

library ieee;
use ieee.std_logic_1164.all;

entity reg_sip_o is
port (clk_in, clear : in std_logic; input_d : in std_logic; q: out std_logic vector (7 downto 0 ) );
end reg_sip_o;

architecture arch of reg_sip_o is 
begin
process (clk_in)
If clear = ‘1’ then 
q<= “00000000”;
 elseif (clk_in’ event and clk_in = ’1’ ) then
q(7 downto 1)<= q(2 downto 0);
q(0)<= input_d;
end if;
end process;
end arch;

VHDL Code for Asynchronous Counter using D flip flop

//*following is the VHDl code for a asynchoronous counter designed with d flip flop *//
library ieee;
use ieee.std_logic_1164.all;

entity dff1 is
port (d_in, clk_in ,clr_in : in std_logic; q, q_bar : inout std_logic);
end dff1;

architecture my_dffbharch of dffl is
begin
process (d_in, clk_in, clr_in)
begin
if (clr_in  = '1') then
if (clk_in  = '1') AND (clk_in'EVENT)  then
q <= d_in;
q_bar <= not (d_in);
end if;
else
q <= '0';
q_bar <= '1';
end if;
end process;
end my_dffbharch;

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity dcoun is
port(clk_in, clr_in :in std_logic;
q, q_b:inout std_logic_vector(3 downto 0));
end dcoun;

architecture arch of dcoun is
component dff1 is
port(d_in, clk_in, clr_in :in std_logic;
qi, q_bar:out std_logic);
end component;
signal k ,p , m :std_logic;
begin
k<=qi (0);
p<=qi (1);
m<=qi (2);
a1:dff1 port map('1','1', rst_in, clk_in , qi(0),q_b(0));
a2:dff1 port map('1','1', rst_in,k,q(1),q_b(1));
a3:dff1 port map('1','1', rst_in, p, qi(2), q_b(2));
a4:dff1 port map('1','1', rst_in, m,qi(3), q_b(3));
end arch;

The Subject of Discussion: Kelvin 4 Wire Resistance Measurement:

• 4 Wire Resistance Measurement| What is a 4 Wire Resistance Measurement?
• Kelvin Bridge| What is Kelvin Bridge ?
• Kelvin Bridge Circuit
• 4 Wire Resistance Measurement Method | 4 Wire Resistance Measurement Technique| What is 4 Wire Resistance Measurement ?
• 4 Wire Resistance Measurement Circuit
• Kelvin Clip Circuit Connection
• 4 Wire Resistance Measurement Application | What are the Applications of 4 Wire Resistance Measurement ?
• Disadvantages of 4 Wire Resistance Measurements | Disadvantages of Kelvin 4 Wire Resistance Measurements
• 2 Wire and 4 Wire Resistance Measurement
• 3 Wire Resistance Measurement
• 4 Wire Resistance Measurement Vs 2 Wire | 2 Wire Vs 4 Wire Resistance Measurement | 4 Wire vs 2 Wire Resistance Measurement
• Frequently Asked Questions

What is 4 Wire Resistance Measurement ?

4 Wire Resistance Measurement

There are different methods to measure different types of resistance, where varies with the range of resistance. 4 wire resistance measurement method is a very accurate measurement method, which can measure very low resistance with high accuracy. It is used to avoid contact resistance or lead wire resistance problems in the circuit. Here every connection wire is called kelvin connection.

In 4 wire resistance measurement method, the four-wire connection is used where two-wire is used to deliver the supply current to the measuring component, and another two-wire is used to measure the voltage drop across the measuring element.

As we know, at constant temperature Ohm’s law define resistance ‘R’ as the ratio of voltage across the resistance to the current ‘I’ passing thru it, So with measuring the voltage drop across the measuring component with known current passing through it, the resistance of the measuring element can be calculated.

What is Kelvin Bridge ?

Kelvin Bridge

The basic principle of the Kelvin 4 wire resistance measurement is based on Kelvin Bridge. Kelvin Bridge is a modified version of the Wheatstone bridge used to measure the very low resistance value, which ranges from 1 ohm to 0.00001 ohms. In this bridge, the effect of load resistance contact resistance and the resistance of the lead wires are taken into account.

Kelvin Bridge Circuit:

Y_b in the figure is the connecting lead wire Resistance.

Whenever the galvanometer is connected to point ‘a’, then the resistance of the connected lead is summed up to the resistance Rx and total impacts become R_x + R_{ab} + R_{cb}.

Whenever the meter is attached  to point ’c’ the resistance of the lead wires  summed up to R₃ + R_{ab} + R_{cb}.

And when the galvanometer is attached to the point ‘b’, which is between ‘a’ and ‘c’ point, in such a way that the ratio of lead resistance from ‘a’ to ‘b’ and ‘c’ to ‘b’ is the same as the ratio of R₁ to R₂.

Equation 1 :

Now the overall equation of the circuit become

Equation 2 :

From equation 1 and 2 after solving we get :

The final equation is the same as the balanced Wheatstone Bridge, which shows that connecting lead wire has been eliminated by connecting the galvanometer at point ‘b’. Y_b is eliminated with the kelvin bridge.

_{Kelvin 4 Wire Resistance Measurement has been described in this article with important concepts} .
_{4 Wire Resistance Measurement Circuit elaborated.
Advantages and Disadvantages of Kelvin 4 Wire Resistance Measurements described.
Difference between 4 Wire vs 2 Wire Resistance Measurement represented.
Important Applications of 4 Wire Resistance Measurement has been described.}

*************************

What is 4 Wire Resistance Measurement ?

4 Wire Resistance Measurement Method | 4 Wire Resistance Measurement Technique

When measuring low resistance, the connecting wires can cause an error in the result of measurement. If the error produced is higher than the tolerance, or if the accuracy of the measurement is required very high degree, then four-wire resistance measurement is used. Ideally, the wire does not have any internal resistance, but in practice, every wire has some internal resistance.

4 Wire Resistance Measurement Circuit:

In the 4 wire resistance measurement method, 4 wire connection is used where two-wire is used to deliver the measurement current to the measuring component, and another two-wire is used to measure the voltage drop across the measuring component.

In this 4 wire resistance measurement method fixed current generator is used. So if the resistance through the circuit varies, the fixed current generator will supply a constant current through the circuit.

The wire which is used in voltage measurement is connected straight to the legs of the resistance, which is to be measured, and the voltage metre is used in this method is of high impedance so that minimal current passes through it. With a small current through the wire, the overall voltage drop across the wire is negligible, which doesn’t affect the value of the measuring component voltage drop. This method eliminates the wire resistance, which is also called Kelvin or four-wire method. Hear special connecting clips are used, which is known as Kelvin clips.

Kelvin Clip Circuit Connection:

Kelvin clips are also known as alligator or crocodile clips. Each half of the jaw of a Kelvin clip is insulated from one another; both Jaws of the Kelvin clip are electrically common to each other, which usually joint at the high point. The current delivering wire is connected to one jaw, and the voltage measuring wire is linked to the other jaw. Kelvin Clips are used when the accuracy of the measurement is required high.

What are the Applications of 4 Wire Resistance Measurement ?

4 Wire Resistance Measurement Application:

• Remote Sensing.
• Resistance thermometer detector.
• Induction hardening.

What are the main Disadvantages of  4 Wire Resistance Measurements ?

Disadvantages of Kelvin 4 Wire Resistance Measurements:

• Expensive.
• Complicated circuit.
• Testing speed is very slow.
• The no. of test points is twice.
• Larger number of connection wires are required.

2 Wire and 4 wire Resistance Measurement

In the 2 wire resistance measurement, the total lead wire resistance adds to the measurement because the current through the whole circuit is the same. As the voltage drop through the wire and the measuring component can produce a measurement with error, It does not have a very accurate output for a small value of resistance when the measuring resistance is much larger than the wire resistance. Then the lead resistance can get negligible. If the length of the wire can be minimum as possible, then the measurement’s accuracy can be increased.

As we can see from the above figure, RW₁ and RW₂ are the lead wire resistance. This is because the Voltmeter measures the voltage drop across R + RW₁ + RW₂ . 2 wire resistance measurement is a less accurate simple circuit structure, requiring fewer connecting wires.

3 Wire Resistance Measurement

3 wire resistance measurement, which is not accurate as 4 wire resistance measurement, is more accurate than two-wire resistance measurement. The complexity of the circuit is less than that of 4 wire resistance measurement.

In this method, the switch is used, so at first, the upper loop of the resistance is measured, the Voltmeter measures the voltage across RW₁ + RW₂, then divide the value by 2, which gives the average resistance of these two wires. RW₃ is assumed to be the same as the avg. of RW₁ and RW₂.

Then, switch the circuit to the regular connection, which measures the measuring component and the resistance of wire RW₂ + RW₃. The calculated value across ( R + RW₂ + RW₃) then compared with the first measured value

which is used to eliminate the lead resistance produced by the wire from the measured value.

3 wire resistance measurement connection can be very accurate if all the three wires connected are of the same resistance value R₁ = R₂ = R₃. 3 wire resistance measurement is widely used in industrial applications, which offers good compromise; it is accurate and uses less wire than 4 wire resistance measurement.

4 Wire Resistance Measurement Vs 2 Wire | 2 Wire Vs 4 Wire Resistance Measurement | 4 Wire vs 2 Wire Resistance Measurement

Parameter	4 Wire Resistance Measurement	2 Wire Resistance Measurement
Connecting wire	4 connection wire	2 connecting wire
Accuracy	Very high even for low resistance measurement.	Very low for low resistance measurement.
Used for range of the resistance	Under 1-ohm resistance	1 ohm to 1 kilo ohm
Circuit design	Complex	Simple
Cost	Expensive	Cheap

Frequently Asked Questions

What is actual working of 2 wire 3 wire and 4 wire types of resistance temperature detector i e RTD ?

RTD stands for resistance temperature detector. It is known that the resistance of a metal changes with the temperature change, so by measuring the resistance with the temperature change, the temperature difference can be detected. They are some metals where the temperature Coefficient is positive, so with the increase in temperature, the electrical resistance of metal increases. RTD can use 2 wire, 3 wire or 4 wire method.

The error introduced by the lead can cause a significant error, so there are very few applications of 2 wire RTD, 2 wire RTD is used with short lead wire or where high accuracy is not needed. Three-wire RTD measurement circuit that minimises the effect of lead wire resistance as long as the connecting wires are of the same length. Some factors such as terminal corrosion or loose connection can still significantly differentiate the lead resistance.

Three-wire RTD is more accurate than two-wire RTD, whereas less accurate than 4 wire RTD, where three-wire RTD is commonly used in the industry relatively cheaper than that of four wires and has a more straightforward Circuit Design than that of a four-wire RTD. In 4-wire resistance measuring, RTD is where the lead wire resistance can be observed and separate from the sensor measurement 4-wire RTD is a true 4 wire resistance measuring Bridge 4-wire RTD is used where high accuracy is needed. Still, it is very expensive and complex in design.

What are the disadvantages of the method of measuring resistance of a wire utilizing an ammeter and a voltmeter in a circuitry ?

Disadvantages depend upon the circuitry’s design, which will measure the resistance for two-wire resistance measurement accuracy is low and for four-wire resistance measurement accuracy is high. In contrast, the two-wire measurement circuit is very simple and cheap, whereas 4 wire resistance measurement is complex and expensive.

The disadvantage of measuring resistance using an ammeter and Voltmeter can be using meters that are not working correctly. The range of the measurement should be considered for the selection of meters, other disadvantage voltmeter and ammeter should be connected to the circuit in different branches. The Voltmeter should be connected parallel to the measuring load, where the ammeter should be connected in series with the branch where the current is to be measured.

To know more about mutual inductance click here

What is the resistance of an electric heater?

According to Joule heating or Ohm heating, heat is proportional to resistance. Joule heating is a process by which electric current passes through a conductor produces heat, so for an electric heater, there must be high resistance in the wire.

What are the factors affecting the resistance?

• Temperature
• Length of the wire area
• Cross-section area the wire
• Nature of material

Will a thick wire have more resistance than a thin wire Why ?

The thin wire usually have greater resistance than a thick wire because the thin wire has fewer electrons to carry the current and In comparison, the thick wire has more electrons to carry the current. In addition, the relation of resistance and area of cross section of a wire is reciprocally proportionate, because of this if cross section of a wire reduce, the value of wire’s resistance will be higher.

How to increase the resistance of a wire ?

The increase in length of the wire or decrease in the area of the cross-section of a wire increases the resistance.

What is the cross sectional area of a wire?

If we cut a wire vertically perpendicular to its length, then we get a circle face of the wire. The area of the circle face of the wire is known as the cross sectional area of the wire and this area of a wire does not depend upon the length of the wire, and it is generally uniform throughout the entire length of the wire.

Why use a high impedance voltmeter ?

Ideal Voltmeter has an infinite impedance that does not consume any current from the circuit. Still, practically e infinite impedance is not possible. A high impedance voltmeter is used. The current that passes through the Voltmeter is very small, so it does not affect the overall circuit.

Is temperature is directly proportional to resistance ? 

The temperature is directly proportional to resistance for a metal conductor or the metal with a positive temperature coefficient.

What are the effects of temperature on resistance?

The effect of temperature on resistance depends on the temp co-efficient of the resistance. This can be defined as the change in resistance per unit change in temperature,if co-efficient is positive, resistance will increase with the temperature rise and if Co-efficient is negative, resistance will decrease with the temperature rise.

Can a wire have zero resistance?

Ideally, zero wire resistance is possible, but practically, no wire present has zero resistance.

Why do we use three-wire RTD?

Three-wire RTD is most accurate when connecting lead wire resistance to three-wire RTD is cheaper than a four-wire RTD and has a less complicated Circuit Design than a four-wire RTD.

What is the benefit of a four-wire resistance measurement?

Four wire resistance measurements can eliminate the lead wire resistance and have resistance measurement having the highest accuracy.

Link to latest article

A D Flip Flop stores a single bit of data; its output mirrors the input (D) when the clock (CLK) is high. Truth table: When CLK=1, if D=0, output Q=0, if D=1, Q=1; When CLK=0, Q remains unchanged. It’s edge-triggered, changing state only at clock edges, ensuring stable data storage and synchronization in digital circuits. Ideal for shift registers, data storage, and synchronizing asynchronous inputs.

A flip flop is the fundamental sequential circuit element, which has two stable states and can store one bit at a time. It can be designed using a combinational circuit with feedback and a clock. D Flip-Flop is one of that Flip Flop that can store data. It can be used to store data statically or dynamically depends on the design of the circuit. D Flip-Flop is used in many sequential circuits as register, counter, etc.

What is D flip flop ?

D flip-flop or Data flip flop is a type of flip Flop that has only one data input that is ‘D’ and one clock pulse input with two outputs Q and Q bar. This Flip Flop is also called a delay flip flop because when the input data is provided into the d flip-flop, the output follows the input data delay by one clock pulse.

Full Form of D flip flop

D stands for Delay or Data in D flip-Flop.

D flip flop Diagram

The given circuit represents the D flip-flop circuit diagram, where the whole circuit is designed with the help of the NAND gate. Here the output of one NAND gate is feed as one input to the other NAND gate, which forms a latch. Then, the latch is gated with two more NAND gates where D is one input and clock is the other input. 

The final output of the D flip-flop is Q and Qbar, where Qbar is always complementary to Q.

D Flip Flop Truth Table

What is D Flip Flop Truth Table ?

The truth table of the d flip flop shows every possible output of the d flip-flop with the all possible combination of the input to the d flip flop, where Clock and D is the input to the D flip-flop and Q and Qbar is the output of the D flip-flop.

CLOCK	D	Q	Qbar
0	0	NO CHANGE	NO CHANGE
0	1	NO CHANGE	NO CHANGE
1	0	0	1
1	1	1	0

D flip flop Excitation Table

The exaltation table or state table shows the minimum input with respect to the output that can define the circuit. Which mainly represents a sequential circuit with its present and next state of output with the preset input and clock pulse. This table is also known as a characteristic table for D flip-flop.

Din	CLK	Present state ‘Q’	Next state ‘Q’
X	0	0	0
X	0	1	1
0	1	0	0
0	1	1	0
1	1	0	1
1	1	1	1

D flip flop Boolean Expression

The boolean expression of the D flip-flop is Q(t+1)=D because the next value of Q is only dependent on the value of D, whereas there is a delay of one clock pulse from input D to output Q.

How D Flip Flop Works ?

Working of D flip flop

D Flipflop is a bi-stable memory element, which can store one bit at a time, either ‘1’ or ‘0’. When the D input is provided to the Flip Flop, the circuit check for the clock signal is the signal of the clock is high ( for level triggered d flip-flop) then with every clock pulse, the input D propagates to the output Q. 

For edge triggered flip-flop, the circuit check for the transition of clock pulse according to which the flip Flop propagates the input to the output; edge triggered can be positive edge triggered or negative triggered. Positive edge triggered D flip-flop changes its output according to input with every transition of the clock pulse from 0 to 1. As for the negative edge triggered D flip-flop changes its output according to input with every transition of the clock pulse from 1 to 0.

D flip flop Timing Diagram

As shown in the given figure, there is a clock pulse representation, with which D, which is the input to D flip-flop, and Q which is the output, is represented, where Qbar is the complement output of the output Q, here we see the timing diagram of a positive edge flip flop, that’s why here the output changes with every positive transition in the clock pulse according to the input.

D flip flop Block Diagram

The diagram shown below is the block representation of the d flip-flop, where D is the input, the clock is another input to the Flip Flop, where a preset and clear signal is used to set or reset the output Q of the D flip-flop. 

What is D flip flop Symbol ?

D flip flop Clear and Preset

The given figure is the block diagram of a D flip-flop having preset/set and rest / clear as additional input to the Flip Flop, where Preset/Set is used to set the output Q of the flip Flop set to 1. Rest/Clear is to set the output Q of the flip Flop to 0.

D flip flop with Set

D flip-flop can have set the input as a requirement, and it can change the output and set the output Q to 1. It can be synchronous or asynchronous, Synchronous when the output can change only with the clock pulse, asynchronous is when the output can be set to 1 at any point of time regardless of the clock pulse.

D flip flop with Reset

D flip-flop can sometimes reset / clear input only in addition to data input and clock input, resetting the output Q to zero of the d flipflop as a requirement. Reset/Clear be active low input or active high input depends on the Flip Flop design.

Asynchronous Set and Reset

D flip flop with Asynchronous Set and Reset

D flip-flop can have an asynchronous set/preset and reset/clear as input independent of the clock. That means the output of the Flip Flop can be set to 1 with preset or reset to 0 with the reset despite the clock pulse, which means the output can change with or without a clock, which can result in asynchronous output.

D flip flop with Asynchronous Reset

D flip-flops can have asynchronous reset, which can be independent of the clock. Regardless of the clock, the reset can change the output Q to zero, which can cause asynchronous output.

D flip flop with Synchronous Reset

D flip-flop with synchronous reset means the output can reset to zero with the reset input but only with the clock, which makes the reset input dependent on the clock pulse; without clock pulse reset will not be able to set the output Q to zero, which will give you a synchronous output always.

D Flip Flop with Enable

Other than set/preset or reset/clear D flip-flop can have enabled as one input when enable is high, the Flip Flop can operate with the data input and clock input, but when the enable is low then regardless of any other input, the flip Flop stays in a hold state.

D flip flop with Enable Truth Table

EnableDQn01NO CHANGE00NO CHANGE111100Table: D flip-flop truth table with enable input

 

D flip flop Truth Table with Preset and Clear

PR (ACTIVE LOW)	CLR(ACTIVE LOW)	CLK	D	Q	Qbar
0	1	X	X	1	0
1	0	X	X	0	1
0	0	X	X	NOT DEFINED	NOT DEFINED
1	1	1	1	1	0
1	1	1	0	0	1
1	1	1	X	NO CHANGE	NO CHNAGE

D flip flop Truth Table with Clock and Reset

CLK	RESET	D	Q
0	X	X	NO CHANGE
1	1	X	0
1	0	1	1
1	0	0	0

Asynchronous D flip flop

When D flip-flop generates output independent of the clock signal, then the output produced may be asynchronous. It is mainly caused by an asynchronous set/preset or clear/reset signal, which can set or reset the output of the flip Flop at any intent of time, which disrupt synchronicity in the D flip-flop.

State Diagram for D Flip Flop

The state diagram is the representation of a different stable state with the transition between the states with the cause of transition. Here every stable state output of the D flip-flop is represented with a circle. In contrast, the transition between the state is represented by the arrow between the circle, which is leveled with the cause of the transition.

When the state changes from 0 to 1, it is caused by the input D, which is high, and when the output state is 0, and at the time D=0 that produces no change in the output, the arrow with D=0 starts with state 0 and also returns to state 0.

ASM Chart for D flip flop

An algorithmic state machine chart contains three blocks: state block, condition block, and conditional output box. The rectangle box represents one state; the diamond box is the condition box true or false if the condition decides the branch to follow.

D flip flop schematic | D Flip Flop Schematic Circuit | D Type Flip Flop Schematic

The figure shows the schematic representation of the D flip-flop; the schematic diagram represents the procedure using abstract. 

Two diagrams show the working of the D flip-flop when the clock is high and another showing when the clock is low. When the clock is high, the input data passes through the circuit, but when the clock is low, the input can not pass through the circuit, which shows regardless of the change in input, there will be no change in output when the clock is low.

Dynamic D flip flop

Flip Flop is generally a static storing device, but a dynamic flip flop can dynamically store data. In the given schematic diagram of a dynamic flip flop, we can see a capacitor connected to each stage. When there is no clock pulse for a long time, the capacitor’s charge can be lost. However, because of the presence of the capacitor, the circuit will be able to store data dynamically.

Dynamic D flip-flop is designed for faster operation; the area covered by dynamic flip flop is less than that of a static flip flop.

D flip flop Metastability

Metastability refers to the state where output is not deterministic. It can cause oscillation, unclear transitions in the circuitry. For example, flip Flop faces the problem of metastability; it happens to a flip flop when the clock pulse and data change at the same instate of time, which causes the result to behave unpredictably.

To avoid metastability in flip Flop the operation of flip Flop should operate considering the setup time and hold time of the Flip Flop. Still, metastability cannot be eliminated completely, but it can be minimized.

Application of D flip flop

Important applications of D flipflop listed as follows :

• D flip-flop can be used to produce a controlled delay in the circuitry.
• Used to design frequency divider circuity.
• For creating counters.
• For developing registers.
• Used in pipelining.
• For synchronization.
• Can be used to avoid glitches.
• Used to fix clock frequency as for the requirement of the circuitry.
• Can be used for isolation.
• As Toggle switch.
• Can be used for Data transmission.
• Sequence generator.
• Can be used as a memory element.

Difference Between D and T flip flop

D FLIP-FLOP	T FLIP FLOP
The output of a d flip flop follows the input with a delay of one clock pulse.	The output of T flip flop toggles with a high input with every clock pulse.
It is known as delay flip flop	It is known as toggle flip flop
With low input the output also changes to low with clock pulse	With low input the output does not change at all, it stays in hold state.

Difference Between D flip flop and JK flip flop

D flip-flop	J K flip flop
The output of a d flip flop follows the input with a delay of one clock pulse.	The output of a J K flip flop sets to 1 with J and resets to 0 with R  when there is clock pulse.
It is known as delay flip flop.	It is also called universal flip flop.
It has less number of input combinations.	It has more number of input combinations.

Difference Between D latch and D flip flop

D latch	D flip-flop
D latch is a gated SR latch, which do not have clock input	D flip-flop is combination of D latch with clock input
Less complex circuit	Complex circuit
D latch is has enable signal which can enable or disable the latch operation	D flip-flop has clock signal which can hold or operated the flip flop when no set or reset input is available.
D latch can be active high input or active low input latch.	D flip-flop in which data input is always active high, where set or reset input can be active high or active low input.
D latch is always a level triggered circuit.	D flip-flop can be level triggered or edge triggered circuit.
Less number of transistor is required for design.	More number of transistor is required for design.
Asynchronous in nature.	Generally synchronous in nature.

Q: What is a flip-flop in digital electronics?

A: In digital electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. They are fundamental building blocks in sequential logic, with the D-type flip flop being a commonly-used type.

Q: What is a d-type flip flop?

A: A D-type flip flop is a type of flip flop circuit that has a D (data) input and a clock input. The D flip-flop captures the value of the D-input at a definite portion of the clock cycle (such as the rising edge). This can be thought of as the flip flop “sampling” the D input and storing it.

Q: How do logic gates interact in a d-type flip flop?

A: A D-type flip flop can be implemented using a combination of logic gates such as AND and OR gates, as well as inverters. The particular arrangement of these gates determines the output of the flip-flop for each input condition.

Q: What distinguishes a d-type flip flop from an sr flip-flop?

A: One key difference is that an SR flip-flop requires two inputs, namely S (Set) and R (Reset), while a D-type flip flop takes both a data input and a clock input. Consequently, the behaviour and use cases of these flip flop types are different in digital electronics.

Q: Can you explain the working of a D flip-flop action on the rising edge of the clock?

A: The D flip-flop is sensitive to the clock edge, i.e., the transition from low to high (rising edge) or high to low (falling edge). When the clock signal goes from low to high on the rising edge, the value on the D input is transferred to the flip-flop’s output. At other times, the output remains what was last stored.

Q: How does a D flip flop compare to a JK flip-flop?

A: The JK flip-flop and the D type flip-flop are two types of flip-flops in digital electronics. The JK flip-flop, like the SR flip-flop, has two inputs but does not have the invalid state that the SR flip-flop has when both inputs are 1. The D flip-flop, on the other hand, eliminates this ambiguity by having only one input that determines what state the flip flop will change to, with the change in state being triggered by a clock edge.

Q: How does a D flip-flop function in shift registers?

A: In a shift register, multiple D flip-flops are chained together in a configuration known as a cascade. Each flip-flop passes its output as the input to the next flip-flop on each clock cycle, effectively shifting the binary data held by the register.

Q: What is a truth table in the context of a D flip-flop?

A: A truth table for a D flip-flop is a table that describes how the output of the flip-flop depends on its current output and current input. For a D-type flip-flop, the next state is exactly what the data input is at the time of a positive clock edge.

Q: What is the characteristic equation of a D flip- flop?

A: The characteristic equation of a D flip-flop is simple: The next output Q(next) equals the current input D (Q(next) = D). This is as per data input from the flip flop at the time of a positive clock edge.

Q: How does a delay flip-flop (D FF) work?

A: A delay flip-flop (D FF), sometimes known as a D-type flip-flop, behaves just like a wire delayed by one clock period. It takes an input signal and outputs that same signal, but delayed by one clock cycle. In essence, the D FF “remembers” the input value at the rising edge of the clock and delays it by one clock cycle.

Q: What is an SR flip-flop in digital electronics?

A: An SR flip-flop, one of the types of flip-flops in digital electronics, is a form of a sequential logic circuit often utilized for data storage. An SR flip-flop requires two inputs, specifically, the set (S) and reset (R) inputs. The output changes or retains its state when it faces different input conditions, making it a fundamental building block of digital electronics.

Q: How does a D-type flip flop work?

A: A D-type flip-flop operates with a data input and a clock input. At the rising edge of the clock input, the d-type flip flop transfers the input data to the output. Thus, it acts as a delay or edge-triggered device in digital electronics, transmitting the data input from the flip flop’s input to its output during clock pulses.

Q: What is a JK flip-flop?

A: A JK flip-flop is another type of flip flop circuit found in digital logic. It extends the functionality of the SR flip flop by addressing the input condition issue where both inputs are 1. With a JK flip-flop, this state triggers a toggle, causing the flip flop to change state at every clock edge.

Q: What are logic gates, and how do they relate to flip flops?

A: Logic gates are fundamental building blocks in digital electronics that process binary inputs to produce a binary output based on the type of gate. Flip flops, including D-type and SR flip-flops, are composed of interconnected logic gates. The combination of these logic gates determines how a flip flop behaves in terms of its characteristic equation.

Q: Can flip flops be used as shift registers in digital logic?

A: Yes, flip flops can be utilized to implement shift registers in digital logic. A shift register is a sequential device that utilizes flip-flops to store binary data. In a shift register, data is passed from the output of one flip flop to the inputs of the next flip-flop in a cascade configuration, in synchronization with clock pulses.

Q: What are the input signals in a flip flop?

A: The input signals in a flip flop vary depending on the type of flip flop circuit used. For an SR flip-flop, the two inputs are known as set and reset. For a D-type flip-flop, the two inputs are data and clock. An additional input, known as ‘enable’, may be used in certain types of flip-flops.

Q: What happens when a flip flop receives a rising edge input signal?

A: When a flip flop receives a rising edge input signal, i.e., a transition from a low voltage to a high voltage, a state change typically occurs. In a D-type flip flop, for instance, the state of the data input is captured at the moment of the rising edge of the clock and is transferred to the output.

Q: What role does an inverter play in the operation of a flip flop?

A: An inverter, another basic block of digital electronics, plays a crucial role in the functioning of a flip flop. It is used in a flip flop circuit to invert the output, specifically, a high output becomes low, and vice versa. In the SR flip-flop, for instance, an inverted output from one part of the circuit is often looped back as an input to another part, creating a form of feedback that enables the flip flop to maintain its state.

Q: What is meant by ‘since the output of a flip flop would always change’?

A: When we say ‘since the output of a flip flop would always change’, we’re referring to the inherent characteristic of a flip flop as a bistable device. This means that it has two stable states and can transition between these states based on its input. Thus, depending on the input conditions and type of flip flop circuit, the output of the flip flop can change or retain its prior state, making it a crucial component in digital electronics where data storage and transfer are required.

Q: What leads a flip flop to change state?

A: A flip flop changes state based on its input signal(s). For instance, an SR flip-flop changes state when either the Set or Reset input is activated, and a D-type flip flop changes state based on the data input at the moment of a clock edge, especially a rising edge. The change state feature of flip flops makes them pivotal in designing digital systems for various applications, from basic data storage units to complex microprocessors.

Content: Master Slave Flip Flop

Master Slave Flip Flop Definition

Master-slave is a combination of two flip-flops connected in series, where one acts as a master and another act as a slave. Each flip-flop is connected to a clock pulse complementary to each other, i.e., if the clock pulse is in high state, the master flip-flop is in enable state, and the slave flip-flop is in disable state, and if clock pulse is low state, the master flip-flop is in disable state, and the slave flip flop is enable state.

Master Slave Flip Flop is also Referred to as.

Pulse-triggered flip flop because the flip-flop  can enabled or disabled by a CLK pulse during this mode of operation.

Master Slave Flip Flop Diagram

Assume that in the initial state Y=0 and Q=0, the next input is S=1 and R=0; during that transition, the master flip-flop is set and Y=1, there is no change in slave flip-flop as slave flip-flop is disabled by the inverted clock pulse, when the clock pulse of master changes to ‘0’, then the information of Y passes through slave and Q=1, in this clock pulse the slave flip-flop is active and master flip-flop gates deactivated.

Master Slave Flip Flop Circuit | Master Slave Flip Flop Circuit Diagram

Master Slave Flip Flop Timing Diagram

The changes in input and output with respect to time can be defined in the timing diagram.

The behaviour of a master-slave flip flop can be determined through a timing diagram. For example, in the given figure below, we can see a signal of the clock pulse, S is the input signal to the master flip flop, Y is the O/P signal of the master flip flop, and Q is the output signal of slave flip flop.

Master Slave Flip Flop Truth Table

The truth table is a description of all possible output with all possible input combinations. In the master slave flip flop, there are two flip flops connected with inverted clock pulse to each other, so in the master slave truth table in addition to flip flop states, there must be an additional column for clock pulse so that the relationship between the input and output with the clock pulse can be determined.  

Application of Master Slave Flip Flop

Mater slave configuration is mainly used to eliminate the race around the condition and get rid of unstable oscillation in the flip flop.

Advantages of Master Slave Flip Flop

Master slave can be operated on level triggered or edge triggered clock pulse; it can be used in various ways.

• A sequential circuit with an edge-controlled flip flop is straightforward to design rather than a level-triggered flip flop.
• By using the Master slave configuration, we also can eliminate the race around the condition.

Master Slave JK Flip Flop

Master slave JK flip-flop could have been designed utilizing 2 JK flip-flops, in that each flip-flop is connected to CLK pulse complementary to each other, and the first flip flop is the master flip-flop which works when the CLK pulse is high state. And at that time the slave flip flop is in the hold state and if the CLK pulse is low state, then the slave flip-flop works, and the master flip-flop stays in the hold state.

The JK flip-flop characteristic is more or less similar to the SR flip-flop, but in SR flip flop, there is one uncertain output state when the S=1 and R =1, but in JK flip flop, when the J=1 and K=1, the flip flop toggles, that means the output state changes from its previous state.

JK Master Slave Flip Flop Circuit Diagram

JK Flip Flop Master Slave Timing Diagram

Master Slave JK Flip Flop truth table

Master Slave JK Flip Flop Working

A master slave flip flop can be edge-triggered or level-triggered, which means it can either change its output state when there is a transition from one state to another, i.e., edge-triggered. The output of the flip flop changes at high or low input, i.e., level triggered. Master-slave JK flip flop can be used in both triggered ways; in edge-triggered, it can be +ve edge-triggered or -ve edge triggered.

In edge-triggered, the master flip flop is derived from the +ve edge of the clock pulse. At that time, the slave flip flop is in the hold state, i.e., the output of the master is according to its input. When the negative clock pulse arrived, the slave flip flop is activated. The o/p of the master flip-flop propagates through the slave flip-flop; at that time the master flip-flop is in the hold state.

Working:

• When J = 0, K = 0, there will be no change in the output with or without clock pulse.
• When J = 1, K = 0, and clock pulse is on positive edge, the output of master flip flop Q is set as high, and when the negative edge of the clock arrives, the output of master flip flop passes through the slave flip flop and produce output.
• When J = 0, K = 1, and clock pulse is one positive edge, the output of master flip flop Q is set as low and Q’ is set as high, when the negative clock edge arrives the Q’ output of the master flip flop feed into the slave flip flop, and that causes to set the output of the slave Q as low.
• When J = K = 1, then at the positive edge of the clock pulse, the master flip flop toggles (means the change of the previous state into its opposite state), and at the negative edge of the clock pulse, the slave flip flop toggles.

Master Slave JK Flip Flop Verilog Code

module jk_master_slave(q, qbar, clk, j, k);
output q, qbar;
input j, k, clk;
wire qm, qmbar, clkbar;
not(clkbar, clk);
jkff master(qm, qmbar, clk, j, k);
jkff slave(q, qbar, clkbar, qm, qmbar);
endmodule
module jkff(q, qbar, clk, j, k);
input j, k, clk;
output q, qbar;
always @(posedge clk)
 case({j,k})
  2'b00:
    begin
     q<=q;
     qbar<=qbar;
    end
  2'b01:
    begin
     q<=0;
     qbar<=1;
    end
  2'b10:
    begin
     q<=1;
     qbar<= 0;
    end
  2'b11:
    begin
     q<=~q;
     qbar<=~qbar;
    end
 endcase
endmodule

VHDL_code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
entity jkff is
port(p, c, j, k, clk: in STD_LOGIC;
q,qbqr: out STD_LOGIC);
end jkff;
architecture Behavioral of jkff is
signal input: std_logic_vector(1 downto 0);
begin
input <= j & k;
process(clk, j, k, p, c)
variable temp: std_logic:=’0’;
begin
if(c=’1’ and p=’1’) then
if rising_edge(clk) then case input is
when “10” => temp:= ‘1’;
when “01”=> temp:= ‘0’;
when “11”=> temp:= not temp;
when other => null;
end case;
end if;
else
temp=’0’;
end if;
q<= temp;
qbar<= not temp;
end process;
end behavioral

Advantages of Master Slave JK Flip Flop

JK flip flop master slave over come the limitation of SR flip flop, in SR flip flop when S = R = 1 condition arrives the output become uncertain, but in JK master slave when J = K = 1, then the output toggles, the output of this state keep changing with the clock pulse.

Application of Master Slave JK Flip Flop

JK flip flop master slave overcome the limitation of SR flip flop, in SR flip flop when S = R = 1 condition arrives the output becomes uncertain. Still, in the JK master slave, when J = K = 1, then the output toggles, the output of this state keeps changing with the clock pulse.

Master Slave D Flip Flop

In this master slave also, two D flip flop connected to each other in series with clock pulse invited to each other. The basic mechanism of this master slave is also similar to other master slave flip-flops. D master slave flip flop can be level triggered, or edge triggered.

Master Slave D Flip Flop Circuit Diagram

Fig. Block representation of master slave D flip flop circuit.

Master Slave D Flip Flop Timing Diagram

In the diagram, one signal of the clock pulse, one is D, the i/p to the master flip flop, Qm is the o/p of the master flip flop, and Q is the o/p of the slave flip flop.

Fig. Master Slave D flip flop timing diagram

Master Slave D Flip Flop Truth Table

Master Slave D Flip Flop using NAND gates

The master slave D flip flop can be designed with NAND gates; in this circuit, there are two D flip flops, one is acting as a master flip flop, and the other is acting as a slave flip flop with an inverted clock pulse to each other. Here for inverter also NAND gats are used.

Fig. Circuit diagram of Master Slave D flip flop designed with NAND gates.

Master Slave edge triggered D Flip Flop

When the state of a flip-flop changes during the transition of a clock, the pulse is known as an edge-triggered flip-flop and these can be +ve edge-triggered, or -ve edge-triggered. The +ve Edge triggered flip flop means the state of it changed during the transition of the CLK pulse from ‘0’ to ‘1’ state. The –ve edge triggered flip flop implies the state of flip flop changes during the transition of the clock pulse from ‘1’ to ‘0’ state.

Fig.  D- type positive edge master slave flip flop.

The positive edge triggered d master slave flip flop is designed with three basic flip- flop as shown in the above figure; S and R are maintained at logic ‘1’ for the output to remain steady. When S=0 and R=1, the output Q=1, where for S=1 and R=0 the output Q=0. When the clock pulse changes from 0 to 1, the value of D transferred to Q,  change in D when the clock pulse is maintained at ‘1’ the value of Q does not get affected by it, and a transition from 1 to 0 also does not cause changes the output Q, nor when the clock pulse is ‘0’.

But in the practical circuit, there is a delay, so for proper output, we need to consider setup time and hold time for proper operation. A definite time before the clock pulse arrives, the requirement of the value of D should be assigned that time is called the setup time. Hold time is the time for which input should behold after the clock pulse arrives.

RS Master Slave Flip Flop

Master slave is a configuration to prevent the unstable behavior of a flip flop; Here in RS master slave flip flop, two RS flip flop are connected to form master slave configuration, here flip flop is connected to a clock pulse inverted to each other; when the positive half of the clock pulse arrives the master flip flop is activated, and during negative clock pulse the slave flip flop is activated. Each flip flop works at different time interval.

In master salve configuration of RS flip flop, an unsalable oscillation cannot take place, because at a time master flip flop is in hold state or the slave flip flop is in hold state. For proper working of mater salve flip flop, we must consider hold time and setup time which can vary from one circuit to another; it depends on the design of the circuit.

Master Slave SR Flip Flop Timing Diagram

Here, there is one clock signal, S is the input signal to the master flip flop, R is also an I/p signal to the master flip-flop, Qm is the O/P of the master flip-flop, Q if the O/P signal of the slave flip-flop.

Master Slave T Flip Flop

FAQ/Short Notes

What do you mean by flip flop? | What is Flip Flop with example?

The flip flop is a fundamental element in the sequential logic circuit, a bi-stable element,  as it has two stable states: ‘ 0,’ and the other is ‘1’. It can store only 1-bit at a time and a flip-flop circuit capable to maintain its state indefinitely or until when power is delivered to the circuit. The O/P state of the flip flop can be changed with input and clock pulse to the flip flop. When a latch circuit is added with some basic gates and clock pulse, it is a flip flop. Example of flip flop is D flip flop, SR flip flop, JK flip flop, etc.

What is S and R flip flop?

In a SR flip-flop, the S stands for the set and R stands for reset;because of this, it is also named as the Set Reset flip-flop. It can be designed with two AND gates and a clock pulse to an SR-latch. When the clock pulse is ‘0’, any input value through S or R cannot change the output value Q, and when the clock pulse is ‘1’, the value of output Q depends on the input values of S and R.

What are the types of flip flop?

There are four types of a flip flop:

1. SR FFs.
2. JK FFs.
3. D FFs.
4. T FFs.

What is a JK flip flop?

JK flip flop characteristic is more or less similar to the SR flip flop, but in SR flip flop, there is one uncertain output state when the S=1 and R =1, but in JK flip flop when the J=1 and K=1, the flip flop toggles, that means the output state changes from its previous state.

JK flip flop can be designed by adding AND gates to the input of S and R in SR flip flop, the input J and output Q’ is applied to the AND gate attached with S and input K, and the output Q is applied to the And gate connected to R.

How does JK flip flop works?

When the clock is not provided, or the clock is low, the input change cannot affect the output. So, for manipulation of output with the input clock, the pulse must be high.

Working of JK flip flop when the clock pulse is high:

• When J = 0 and K = 0, there will be no change in the output.
• When J = 0 and K = 1, then the value of output will get reset.
• When J = 1 and K = 0, then the value of output will get set.
• When J = 1 and K = 1, the output value gets toggled (means to switch to the opposite state). In this state, the output will continuously change with the clock pulse.

Why JK flip flop is used?

JK flip flop is more versatile than D- flip flop or SR flip flop; they can operate more function than any other flip flop, they are widely used to store binary data. JK flip flop also overcome the uncertain states of SR flip flop.

How does JK flip flop toggle?

When the input to the flip flop J = K = 1 with clock pulse high, that’s when the JK flip flop toggles.

Why D flip flop is called delay?

The next output state of the D flip flop follows the input D, when the clock pulse is applied, in this way the input data is transfer to the output with delay, that’s why it is called a delay flip flop.

What are the applications of flip flop?

The flip flop is generally used as a

• The memory elements. 
• In the shift-registers. 
• The digital counters.
• The freq. Divider circuits.
• The bounce elimination switch, etc.

What are the characteristics of flip flop?

It is a synchronous sequential circuit; it changes its output state only when the clock pulse is present. It is the basic memory element for any sequential circuit, it can store one bit at a time. It is a bistable device.

What is the difference between D and T flip flop?

• D flip flop can not take similar input as D and D’ is its two input, so the input is always complementary to each other. On the other hand, Both the input in T is the only T so both inputs to the T flip flop will always be the same.
• D flip flop is a delay flip flop, in this flip flop, the output follows the input with the arrival of the clock pulse, whereas the T flip flop is called a Toggle flip flop, where the output changes to the opposite state with every arrival of the clock pulse when the input is 1.

Where are D flip flop used?

It is commonly used as a delay device or to store 1-bit data information.

Combinational Logic Definition

Combinational logic is a type of logic in which the output can only be modified by present input.

Combinational Logic Circuits| What is Combinational Logic Circuit

Combinational circuitry is a type of circuitry in which the current input can only modify the current output.  This circuit is also known as the clock independent circuit because for operation is doesn’t need a clock. This circuit doesn’t have a memory element or any feedback path, so the circuit can’t store any data. A combinational circuit can design by combining the logic gates. The circuitry used in combinational logic is used as coding, decoding, error detection, manipulation, etc. The basic circuits of combinational logic are multiplexer, decoder, encoder, shitter, Adder, Subtractor, etc.

Fig. Block diagram of a combinational circuitry.

A combinational logic circuit can have ‘n’ number of input variables and ‘m’ number of the output variable. For the ‘n’ input variable, there is 2ⁿ possible combinations of input variables. For each unique combination of input variables, there is only one possible output combination. The output function is always expressed in terms of the input variables. A truth table or Boolean equation can determine the relationship between the output and input of a combinational circuit.

Types of Combinational Logic Circuits

The classification of the combinational circuitry is based on the application they being used:

1. Arithmetic and Logical circuit: Adder, Subtractor, Comparators, etc.
2. Data Transmission: Multiplexer, Demultiplexer, Encoder, etc.
3. Code Converter: Binary code converter, BCD code converter, etc.

Combination Logic Gates

Combinational logic gates are the fundamental gate which is combined to form any circuitry in the digital electronic. A logic gate is ideal for implementing an essential Boolean function—for example, gate, NAND gate, OR gate, NOR gate, etc.

AND gate:

AND gate has two or more input with one output. The output is high means ‘1’ when all the input is high; otherwise, the outcome is low means ‘0’.

Fig. Logic diagram of AND gate

OR gate:

OR gate has two or more input and one output. The output is high means ‘1’ when at least one input is high; otherwise, the result is low, which means ‘0’. But in commercial OR gate with 2,3 and $ input types is available.

Fig. Logic diagram of OR gate

NOT gate:

NOT gate has one input with one output. When the input is high means ‘1’, then the NOT gate’s output will be low, which means ‘0’.

Fig. Logic diagram of NOT gate

NAND gate:

NAND gate means NOT AND, here AND gate output feeds into NOT gate. NAND gate can be designed from the AND gate truth table by complementing the output variables. The result of the NAND gate is low when all the logic input ishigh. Otherwise, the output is high.

Fig. Logic diagram of NAND gate

NOR gate:

NOR means NOT OR gate. Here OR gate output is feed into NOT gate. NOR gate designed from the OR gate truth table by complimenting all the output variables. The output of a NOR gate is high when all inputs are low. Otherwise, the output is low.

Fig. Logic diagram of NOR gate

XOR gate:

XOR gate means Exclusive-OR gate, also known as EX-OR gate, it has two input and one output. For two input gates, the output of the XOR gate is high, which means ‘1’ when the input bit is unlike, and output is low means ‘0’ when there is like input.

Fig. Logic diagram of XOR gate

XNOR gate:

XNOR means Exclusive-NOR gate, also known as EX-NOR; it is NOT of EX-OR. The output of a two-input XNOR gate is high, which means ‘1’ when the input is like and Low when, unlike input.

Fig. Logic diagram of XNOR gate

Combinational Logic Examples| Combinational Logic Circuits Examples

Half Adder:

Half adder is an example of combinational circuitry, in which we can add two bits. It has two input, each of one bit and two output, in which one is carry output, and the other is for sum output.

Fig. Logic diagram of half adder designed with AND gate and XOR gate.

Full adder:

Full adder is an example of the arithmetic combinational circuit; here, we can add their bit at a time, and has two output sum and carry. In half adder, we could only add two bits at a time. A full adder overcomes that limitation; a full adder is essential for adding a huge binary number. However, one full adder can add an only one-bit binary number at a time, but by cascading the full adder, we can add a more extensive binary number. However, we can create a full adder by combining two half adders.

Fig. Block diagram of full adder

Half Subtractor:

A half subtractor is an arithmetic combinational circuit that performs subtraction of two input bit and provides two outputs, one as a difference and the other as borrow. Designing the subtractor circuit is mainly similar to that of an adder. I cannot consider any borrow input.

Fig. Logical diagram of half subtractor designed with AND gate, NOT gate and XOR gate.

Full Subtractor:

Full subtractor is also an arithmetic combinational circuitry, where we can perform subtraction of three one-bit inputs, inputs are the minuend, subtrahend, and a borrow. It generates two outputs, one as the difference of the input and the other as borrow.

Fig. Block diagram of full subtractor.

Multiplexer:

The multiplexer has multiple inputs and a single output, and it has a selector line that selects one input at a time as the requirement. It sends it to the output line, and for the ‘n’ number of input here, we need the ‘m’ number of the select line where n = 2^m. It also has an enabled input line, enabling us to cascade multiplexer or further expansion as required.  It is also called a data selector.  16: 1 Is the largest multiplexer available in IC form.

Fig. Block diagram of Multiplexer.

Demultiplexer:

Demultiplexer has only one input and multiple outputs. It has a selector line that selects one output line at a time; with the select line, we can distribute the input signal into many output lines as our requirement. For the ‘n’ number of output line here, we need the ‘m’ number of the select line where n = 2^m. Demultiplexer can work as a binary to decimal converter.

Fig. Block diagram of Demultiplexer.

Comparator:

A comparator is a combinational circuit where it can compare the magnitude of a two n-bit number and provide us with the relative result as output. It can have three outputs. For example, the input we provide A and B to the comparator where A and B can be an n-bit number the output of the comparator can be A<B, A=B, A>B. The circuit checks the magnitude of the input and compares it; there is a different output port for A=B, A>B, and A<B. When the comparing of the magnitude is done, the respective output get. As a result, the output can be active low or active high depends on the circuitry.

Fig. block diagram of n-bit comparator

Encoder:

The encoder is a combinational circuit. It has 2ⁿ input lines and has ‘n’ output lines corresponding to the n-bit code input.

Fig. Block diagram of Encoder.

Decoder:

It is a circuit that converts binary n input lines to a maximum 2ⁿ output lines.

Fig. Block diagram of a decoder.

BCD adder:

A BCD adder is an arithmetic combinational circuit used to operate addition on BCD numbers, digits and produced output in BCD form. Sometimes the output of a BCD adder may be a valid BCD number, and then it converts that invalid BCD number into valid by adding 0110 to the invalid output.

BCD subtractor:

A BCD subtractor is to operate the subtraction on the BCD number. If we take two input BCD number, one as A and the other as B, subtraction of the BCD number is equivalent to the addition of a compliment of B to A. In BCD, subtraction 9’s complement or 10’s complement method is used.

ALU (Arithmetic Logical Unit):

 The circuitry of the Arithmetic logical unit is widely used as a combinational circuitry, and This circuitry is used to perform all the arithmetic and logical operation for and processor. ALU is known as the heart of a microprocessor or microcontroller.

Combinational Logic with MSI and LSI

MSI stands for “Medium-scale integration”, it can contain 30 to 1000 electronic components in a single chip of IC. LSI stands for “Large scale integration”, It can have thousands of embedded components and integrated on a single IC.

Adder with MSI and LSI:

TRUTH TABLE:

A	B	C	S	C
0	0	0	0	0
0	0	1	1	0
0	1	0	1	0
0	1	1	0	1
1	0	0	1	0
1	0	1	0	1
1	1	0	0	1
1	1	1	1	1

Equation for sum:

S=AB’C+A’BC+AB

Carry:

C=AB’C+A’BC+AB

Fig. Implementation of Full-Adder in MSI or LSI circuitry.

Combinational Logic Design |Design a Combinational Logic Circuit

The Objective of Designing Combinational logic:

• To get desired output from the circuitry.
• An economic circuitry means with minimum expenses building a circuitry.
• The complexity of the circuitry must be reduced as much as possible.
• With a minimum number of gates, a digital circuit should be designed to minimize the overall circuit delay.

The combinational circuit can be designed with the multiplexer, procedure for designing:

• Determine the number of input and output variables of the required circuit.
• Get the truth table or logic diagram of the required circuit.
• From the truth table or logic, the diagram determines the Boolean expression of the required circuit and expands it into minterms, and each defines a unique data line of the multiplexer.
• For ‘n’ number of input, variables get 2ⁿ to 1 multiplexer.
• With the help of a select line and input, you can get output from the multiplexer according to your desired circuit.

Combinational Circuit Design Using Logic Gates

Designing a combinational logic circuit can be done with gates, whereas gates are practically available as IC. For different gates, there are other IC available with different IC numbers.

Steps or procedure to get the required combinational logic circuit:

• Determine the number of input or output variables required for the operation through the given truth table, Boolean statement, or expression.
• Derive the expression in the form of a sum of product (SOP) or product of sum (POS).
• Reduce the expression using the Boolean reduction method or K-map.
• You can design the circuit with the required number of gates in the logic diagram through the reduced expression.

Functions of Combinational Logic

The functions of a combinational logic can be defined with Truth Table, Logic Diagram or Boolean Equation.

Truth Table: Truth table is a tabular list of all possible binary combinations of the input variable and related output combination of a logic circuit. There are only two possibilities of an input or output bit, i. e. ‘0’ and ‘1’. If the number of input is ‘n’, there will be 2ⁿ combinations. In this table, there is one row for representing input combinations as well as different rows for output combinations. This can be obtained from the logic diagram or Boolean expression of the circuitry.

Logic Diagram: The logic diagram is mainly composed of a basic logic gate and some symbolic representation of the circuit. It shows us the interconnection of logic gates, represents some signal lines (like enable, select line, control lines, etc.). It is used to define the functionality of circuitry. It can be obtained through Boolean expression or the truth table of the circuitry.

Boolean Expression: This is an equation formed from the combination of input and output variable; here, the expression is mainly used to define the input variable’s output variable. This expression can be derived from the truth table or the logic diagram of the circuitry.

Combinational Logic Circuit Real Life Examples

In real life, we can see the combinational circuit in calculator, RAM (Random Access Memory), Communication system, Arithmetic and logic unit in CPU (central processing Unit), Data communication, wi-fi, cell phone, Computer, etc. These are a real-life example of where the combinational circuit is used.

Analysis Procedure in Combinational Logic

Combinational circuit analysis is the analysis of a given logic circuit or a circuit diagram; from here, we can gather information regarding the circuit. An analysis is to verify the behaviours of the circuitry with its specifications; analysis of a circuit can be used to reduce the number of gates, optimise, reduce delay, or convert the circuit into another required form.

Analysis procedure of combinational logic:

• Determine the output variable of the circuitry, and try to get a truth table or logic diagram of the circuit with input and output variables.
• Through a truth table or logic diagram of the circuitry, define the Boolean function with the help of input and output variables.

Verilog for Loop Combinational Logic

What is a combinational loop?

The combinational loop is a loop in which the output of a combinational logic(which can consist of one or more combinational logic gates) is feedback to the same logic without any memory element in the feedback path.

Types of the combinational loop:

• Not equivalent to latch
• Equivalent to latch

Fig. Combinational loop type latch

Verilog for loop combinational logic:

If(sel==1’b0)

Y=I0;

else

Y=Y;

Here combinational loop implemented, which is equivalent to latch.

CMOS Combinational Logic Circuits| Combinational Logic Networks

Static CMOS is widely used for circuitry because it has good performance, low power consumption. A CMOS gate is a combination of a pull-up network (PUN) and Pull-down network (PDN); an input is distributed to both pull-up and pull-down circuits.

The function of the pull-up network is to connect the output with the voltage source when the output needs to be ‘1’. Whereas a pull-down network provides the connection between the ground to the output when the output is meant to be ‘0’. Pull-down network is designed with NMOS, and PMOS is used in PUN. NMOS is connected in series to form AND function, whereas when connected in parallel from OR function. Where PMOS in parallel form output as NAND function and series form NOR function.

Fig. CMOS diagram of half adder.

 CMOS is a complementary network. This means for parallel connection in pull-up network there is the series connection in pull-down network. The complementary gate is generally inverting. With one stage, it can perform a function such as NAND, NOR, and XNOR, and for non-inverting Boolean function such as AND, OR and XOR, it required an extra inverter stage. The number of transistors for implementation of n- input logic gate is 2n.

MUX Combinational Logic

MUX i.e., Multiplexer is a combinational logic design, it has only one output and can have multiple input. It has ‘n’ select line for2ⁿ input, selector line s use to select which input line will be connected to the output line.

Fig. Block diagram of a 4:1 multiplexor

TRUTH TABEL OF 4:1 MULTIPLEXOR:

S1	S2	Y
0	0	I0
0	1	I1
1	0	I2
1	1	I3

Simple Combination Lock Using Logic Gates

A simple combinational look is a circuit designed with XOR and NOR gate, where XOR gate is a bit comparator, and NOR gate is used as a controlled inverter. We can use XOR to check and compare the input and the key code bit by bit; if the input completely matches with the key code, the lock will be unlocked. When the inputs and not the same XOR provide ‘1’ as an output, now the output will go through the NOR gate. In this way, we can design a simple lock using gates.

Combinational Logic Circuits Applications

Combinational logic circuits are the basic circuit in digital electronic even sequential circuit is designed from the combinational circuit with the memory element.

These circuits are used for designing the ROM of a computer or a microprocessor. ROM (Read Only Memory) is designed with Encoder, Decoder, Multiplexer, Adder Circuitry, Subtractor Circuitry, etc., which are all combinational circuits.

Whereas ALU (arithmetic and logic unit) in the processor, which is also from the combinational circuit, mainly consists of Adder, Subtractor, etc., to perform every arithmetic operation.

Encoder and decoder are used to convert one form of data to another (like from Binary to Decimal); these are commonly used in communication for transferring data from one end to another. This circuit provides synchronization if needed; with the help of these, we can perform any operation with greater accuracy.

A multiplexer is used to transfer data in a single line. This circuit is used in broadcasting, telegraphy, etc.

Disadvantages of Combinational Logic Circuits

The limitation or disadvantage of half-adder is overcome by a full adder, whereas the full subtractor overcomes the restriction of half subtractor.

Disadvantages of Multiplexer: Limitation of using the port, which can use in a specific sequence. The circuitry can cause delay.

The disadvantage of Demultiplexer: wastage of bandwidth, delay can from due to synchronization.

Disadvantages of Encoder: Complex circuitry can be easily subjected to magnetic interference.

Overall, the combinational circuit is complex as the circuit is getting bigger; in bigger circuitry, there can be high propagation delay, it doesn’t have any memory element.

Combinational logic circuits MCQ | Combinational logic circuit problems and solutions | FAQ

What is combinational logic What are its characteristics ?

Described in Combinational logic circuit section.

What is 1*4 Demultiplexer in Combinational Logic Circuits ?

A 1 to 4 Demultiplexer has two select line, four output and one input. The input data connected to the output line according to the select line.

Fig. Block diagram of 1:4 Demultiplexer

Truth Table:

INPUTS				OUTPUTS
S1	S0	Y3	Y2	Y1	Y0
0	0	0	0	0	1
0	1	0	0	1	0
1	0	0	1	0	0
1	1	1	0	0	0

Can you ever have metastability with pure combinational logic ?

Yes, there can be a metastability state for some time in pure combinational logic.

             Metastability refers to the state which cannot be defined as ‘0’ or ‘1’. Usually, this happens to a circuit when the voltage is stuck between ‘0’ and ‘1’, which can cause oscillation, uncertain output, unclear transition, etc. When such a signal goes through the combinational circuit, it can violate basic gates’ specification and spread through the overall circuit.

For example, when taking the given circuit, as we see here, there is an AND gate and a NOT gate, practically a circuit has some propagation delay; as AND gate has some propagation delay, the NOT gate has to. As we know, the output should be defined at all times, but there is a time interval T where the output state or the transition state is not definite or undesirable. That state at that time interval can be considered as metastability of a pure combinational logic circuit.

Design consideration of different combinational logic circuits in VHDL.

For designing circuitry, you must know the basic of VHDL, such as representing a Boolean function, representing a fundamental gate, etc.

Here we considering full-adder as an example:

In VHDL:

Entity FullAdder is

Port (A, B, C: in bit;

D, S : out bit);

end FullAdder

Advantages of design and testing of combinational logic circuits using self in test scheme

Advantages:

• Lower cost for testing.
• Fault can be easily detected.
• Shorter test time.
• For higher reliability on the circuit, a self-test scheme s used.

What is the diffrence between combinational and sequential logic ciruit?

To know about sequential logic click here.