Hi, I am Sudipta Roy. I have done B. Tech in Electronics. I am an electronics enthusiast and am currently devoted to the field of Electronics and Communications. I have a keen interest in exploring modern technologies such as AI & Machine Learning. My writings are devoted to providing accurate and updated data to all learners. Helping someone in gaining knowledge gives me immense pleasure.
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“A potentiometer is an electrical device that changes the resistance value to control the flow of current and also measures emf of a cell.”
A potentiometer, also known as ‘pot‘ is a passive and three-terminal device. Though pot and variable resistors (rheostats) seem to be the same device, they differ in their connections within a circuit. It is an electrical device rather an electronic device.
What does a potentiometer do?
A pot limits the current flow by providing resistance value. That means it can increase or decrease the current of a circuit. It also works as an adjustable voltage divider. Based on this functionality, a pot can measure the electrical emf also.
The ‘k’ represents kiloohms. The numeric value tells the value of resistance. 1k means that the pot will provide resistance up to 1000 ohm. 10k & 100k means it will provide ten times and 100 times more resistance than 1k, respectively. The lesser the resistance value, the more the current drawn by that pot. Similarly, a 500k pot means it has a resistance value between 0 to 500 kiloohm.
How does the potentiometer work?
Basic Structure of a Pot
Potentiometers have some basic working principles. A pot has two terminals as input (marked as red and green in the figure). The input voltage is applied – across the resistor. Then the output voltage is measured. It comes out as the difference between the fixed and moving contact. The wiper plays a vital role here. While optimizing the output voltage- as per the need, the wiper needs to be moved- along the resistive element. Moving the slider helps to balance the galvanometer in case of measuring the emf of a cell. Now it acts as a voltage divider as it continuously produces variable voltage. Based on this concept, a pot measures electrical emf.
How does a potentiometer work as a voltage divider?
When the pot’s slider is moved- to the right, that causes a fall in resistance, fall in resistance further causes a small voltage drop. After that, if the wiper is moved- to the left, the resistance value eventually gets increased. Noe, there is also a voltage drop, but this time it is more than the previous case. So we can conclude that the output voltage has a direct relationship with the position of the wiper. The voltage drop value is calculated -by subtracting from the source voltage.
Pot as a Voltage Divider
Types of Potentiometers
Based on shape, there are mainly two types
They are –
A. Linear pot.
B. Rotary pot.
Linear potentiometer:
In this type of pot, the slider moves linearly. Some different types are –
Slider potentiometer or slide pot:
If the wiper moves, in left-right or up-down direction, to adjust the pot, then it is slide pot. Slide pots find its application in audio, where it is known as faders.
If a servo motor controls a slide pot’s slider, the pot is called a motorized slide pot or motorized fader. It has applications in audio control, where automatic control is required.
B. Rotary Pot
In this type of pot, the slider moves circularly. Some different types are –
Single – turn pot:
In a rotary pot, if it takes a single turn to control the pot, this type of rotary pot is known as a single turn pot. It takes approximately 3π / 2 degrees.
This type of pot requires multiple rotations of the slider. It generally takes 5-6 turns. It provides high precision and controls, that is why it has application in calibration circuits.
The symbol of a pot is a standard resistor symbol with an arrow. Note that a variable resistor or rheostat symbol is also a resistance symbol with an added arrow, but the arrow’s position differentiates the devices.
The IEEE standard symbol of Pot
The IEC standard symbol of Pot
Difference between rheostat and a potentiometer?
There is a misconception that a rheostat and a potentiometer are the same things, but there are some differences. Let us discuss some of them –
Subject of Comparison
Potentiometer
Rheostat
Number of Terminals
Three terminal device
Two terminal device
Connection in Circuit
Parallel connection
Series connection
Quantity Controlled
Controls Voltage
Controls Current
Application
Low power application
High power application
Number of Turns
Both single and multi-turn
Single turn
Resistive material
Materials like Graphite
Carbon disk, Constantan, Platinum, etc
Symbol
Frequently asked questions
1. What is the resistive element composed of a potentiometer?
The resistive element is the cause that a pot can offer resistance. Generally, Graphite is the material for making resistive elements. Sometimes they are also made of carbon materials, resistive wires, ceramic metal mixtures, etc.
2. What is a digital potentiometer?
A digital pot is a digital device. It performs the same task as an analog pot does. It has found application in microcontroller electronics.
3. What is a logarithmic potentiometer?
A logarithmic pot changes its resistance value logarithmically. It comes under the non-linear type.
4. What are the parts of a potentiometer?
A typical pot consists of – two fixed terminals and a moving terminal. It also has a resistive element. By using the two fixed terminals, potentiometers take the input. The other part is a wiper or slider.
5. Does a potentiometer reduce voltage?
No, a pot doesn’t change the voltage of the circuit. It only controls resistance.
6. What is a potentiometer knob?
A pot knob is a holder for the slider of a rotary pot. By rotating the knob, the resistance changes.
7. How to compare – the emf of two cells using a pot?
EMF or electromotive-force is a parameter of measuring energy. It is the reason behind the flow of current in a circuit. The potential difference between two points is referred- to as electromotive-force. Its unit is volt.
The mathematical formula is – e = E / Q, where q is the charge, and E is the energy. By using a pot, we can find the emf of a cell. We need to find out the balancing length, where the galvanometer deflection is nearer to null. The potential fall along the length l is the measure of the emf. E is proportional to l.
We can write,
E ∝ l
or, E = K * l , K =Constant
or, E / l = k ———- (i)
Now relation of E1 and l1 with E2 and l2 can be written using equation (i) –
E1 = k * l1
or, E1 / l1 = k ——— (ii)
E2 = k * l2
or, E2 / l2 = k ———(iii)
From (ii) and (iii) we can write –
E1 / l1 = E2 /l2 = k
or, E1 / l1 = E2 / l2
8. A cell with internal resistance 1 ohm and emf 5 volts balances on a potentiometer wire at a length of 1.25 meters. The driving cell has an emf of 50 volts. If a 1-ohm wire connects the balance point and the battery, then the balance point will shift.
(Assuming that balancing length is measured from the higher potential side of pot wire.)
A. 1.25 meters towards the right
B. 1.25 meters towards the left
C. 2.5 meters towards the left
D. None of the above
At first, the balanced length is 1.25 m. Let’s consider it as l1.
Now a wire of 1-ohm resistance connects the balance point and the cell.
We know that E = k * l
Here, l = l1 and E = 5v
k * l1 = 5 – (i)
Now the current through resistance is = (5/2) A = 2.5 A
By adding up the resistance of 1 ohm, the equivalent resistance comes as = 1+1 = 2 ohm.
Hence the E value for the later case becomes 2.5 v.
k * l2 = 2.5 – (ii)
We know that –
E1/E2 = l2/l1
from equations (i) and (ii), we find out –
5/2.5 = l2/l1
putting l1 in the equation,
l2 = 0.5 * l1
or, l2 = 0.5 * 1.25
or, l2 = 0.625 m
So, the balance point shifts 0.625m towards the left.
The correct answer is the option – D. None of the above.
9. A potentiometer is better than a voltmeter for measuring emf of a cell. Why?
When we balance a cell against a pot wire, There is no current through the cell. The emf is measured then. Now, when we use a voltmeter to measure the emf for the cell, there is a small current which flows through the cell. Thus, we get only the terminal potential.
10. How can you increase the accuracy of the potentiometer?
The accuracy of a pot can be increased by maximizing the length of the wire up to a certain limit.
In this article, we will study detail about notch-filters.
Notch Filter Definition
Before discussing in detail about notch-filter, let us find out the definition of it. A notch-filter can be defined as a band stop that has a very narrow frequency bandwidth. Great depth, high-quality factor, and sharpness in band-reject characterize a notch-filter. There are several kinds of notch-filters which we will discuss later.
Checkout these two articles for more details –
Notch Filter Equation
Some of the important equations of notch-filter are given below.
The HF cut-off of the LPF: fL = 1 / ( 2 * RLP * CLP * π)
The LF cut-off of the HPF: fH = 1 / ( 2 * RHP * CHP * π)
The quality factor of the notch filter: Q = fr / Band Width
How does a notch filter work ?
Working of notch filter
A notch-filter has the same working principle as of band-reject filter. It allows all other frequency components of the signal and blocks the specified narrow bandwidth. For a passive design, the resistive, capacitive and inductive reactance play the part of controlling the frequency.
Notch filter graph | Notch filter phase response
The following is the notch-filter graph.
Notch Filter Q
Q of a notch-filter is a very important parameter. Q or Quality Factor of a Notch-filter is given by the following equation: Centre Frequency/Bandwidth. Q is the measurement of the selectivity of the filter.
The center frequency is the Notch Frequency, and it is the center frequency of the passband.
Notch filter applications | Use of notch filter
There are several applications of different kinds of notch-filters. Let us discuss some of them.
Communication Systems: Notch-Filters is one of the important pieces of equipment for a communication system. There is a high probability that the message signals get interfered with by harmonic noises in long-term communication. Notch-filters eliminate the noise.
Audio Engineering: One of the basic components of audio engineering is a notch-filter. Eliminating noise, spikes are some of the tasks performed by a notch-filter.
Medical Engineering: Notch-filters have been used in Medical Engineering. Reading of EEG is impossible without a notch-filter.
Digital Signal Processing: Notch-filters have applications in Digital Signal Processing. A notch-filter is important when there is a need for mixing up signal or condition of elimination of certain frequency component.
Digital Image Processing: Notch-filters help to eliminate noises from digital images.
Optical Applications: Notch-filters have applications in optical applications. Blocking off a certain wavelength of light is done by specific optical notch-filters.
Notch filter EEG
EEG or Electroencephalogram is a very important process in medical sciences. Several filters are used to display the output data produced by the machine. Without the filters, it is quite impossible to read the values.
There are three kinds of filters used in an EEG reading. They are – high pass filter, low pass filter, and notch-filter. High pass filter filters out high-frequency components, whereas low pass filters do the same for common frequency components. The notch-filters filter out a certain given range of frequency.
Especially the supplied frequency of the AC interferes with the EEG readings. Notch-filter removes such interference. For North America, the supply frequency is 60 Hz, so a 60 Hz notch-filter is used. In India and other countries where the supply frequency is 50 Hz, a 50 Hz notch-filter is used.
Optimum notch filter in image processing
There is certain kind of periodic noises in digital images. The noises are repetitive and unwanted. They create certain patterns and affect the picture badly. One of the solutions to the problem is an optimum notch-filter.
At first, the noise frequency is determined, then the notch-filter produces the repetitive noise, and the output with lesser noise is produced.
Notch filter transfer function
The following expression gives the transfer function of a notch-filter –
Here, wz refers to the Zero-Circular Frequency, whereas wp refers to the pole-circular frequency. Finally, q means the Quality Factor of the notch-filter.
How to use a notch filter ?
When there is a need to reject a certain narrow band of frequency, a notch-filter is used. A notch-filter is placed after any source from which the signal needs to be eliminated. In most cases, the filter is set as the very last component of any circuit.
Difference between notch filter and band stop filter
A notch-filter is one type of bandstop filter. The only difference between a band stop filter and a notch-filter is that a notch-filter has a narrower bandwidth than a normal bandstop filter.
Bandpass vs Notch filter
There are some differences between the bandpass filter and the notch-filter. Let us elaborate on them.
Points of Discussion
Bandpass Filter
Notch-Filter
Principle
Allowing certain band
Rejecting certain band
Bandwidth
Comparatively wider band is passed.
A comparatively narrower band is rejected.
Anti notch filter
Notch-filters reject the very narrow bandwidth of signals and allow other components of that signal. The same but opposite task is performed by bandpass filters. The bandpass filters allow passing a certain band of frequency and block different parts of the movement.
Notch filter characteristics
Some of the attributes of a notch-filter –
Narrow bandwidth
High Q value
Great depth
Notch filter high q
Twin T notch-filters can provide a very good amount of depth, almost infinite. If an LM102 voltage follower is added to the network, the Q of the circuit gets a skyrocketing growth from 0.3 to 50. That is how a high Q is achieved.
Gain of notch filter
The gain of a notch-filter can be calculated using the following equation.
Notch filter coefficients
Notch-filter coefficients are referred to as the coefficients of the transfer functions.
Here, wz refers to the Zero-Circular Frequency, whereas wp refers to the pole-circular frequency. Finally, q means the Quality Factor of the notch-filter.
Transfer function of notch filter in s domain
The following expression gives the transfer function of a notch-filter –
Different types of Notch-Filters
Active notch filter
An active notch-filter is a combinational circuit of two separate circuits. For example, connecting a low pass filter and a high pass filter in a parallel connection and adding an op-amp for amplifying purposes will work as an active notch-filter.
Inverse notch filter
Inverse notch-filter is a special type of Notch-filter that has an infinite impulse response. Inverse notch-filters are very useful in medical image processing where there is a need to eliminate narrowband signals. Inverse notch-filters do the job efficiently.
Cavity notch filter
Notch-filters are a special type of Cavity filter. Cavity filters allow a certain narrow band of frequency. So, we can say that the working is the same as notch-filters. That is why often cavity filters and-notch-filters are termed cavity notch-filters.
Adjustable notch filter | Adaptive notch filter
Adjustable notch-filters are also tunable notch-filters. One can adjust the frequency as per the need. Some of the Adjustable notch-filters are very important in audio engineering.
Adjustable q notch filter
Adjustable q notch-filters can change the Q value of the notch-filter. Therefore, the Q is a very important parameter of the filter.
The adjustable Q value is needed for the audio engineering department.
Bandpass notch filter | Notch band pass filter
Notch-filters are a special type of bandpass filter. Bandpass filters allow a certain band of frequency to pass. In bandpass filters, theoretically, any range of rounds can be given by the required design. But, in bandpass filters, the band’s scope is typically narrower than the usual ones.
Notch filter VST
VST is a filter envelope plugin. An envelope provides several edges to a filter. VST notch-filters offer many advantages like mixing up audios very finely, etc.
FM Notch filter
FM notch-filters or Frequency Modulation notch-filters are some of the important instruments for Software-Defined Radios. Even these filters made the Software-defined Radios popular. It also helps in radio communications.
Tunable fm notch filter
Tunable FM notch-filters are special kind of notch-filters which can adjust the center frequency as per the need of the applications. No need to say again that the FM filters need the tunable filters because several frequency bands need to be blocked from a signal in FM.
RF Notch filter
RF or Radio-Frequency Notch-filters are used to reject only one frequency from a given band of frequency. Generally, RF notch-filters have a Q. Basic RF filters are designed from low-pass filters to achieve high efficiency. However, converting them into a notch-filter is a tough process and needs a high level of caution and efficiency.
Tunable notch filter RF
Just like other tunable notch-filters, the tunable rf notch filter can adjust the frequency band as per the need.
60 Hz Notch filter EEG
EEG or Electro-Encephalograph Machines has an inbuilt 60 Hz notch-filter. The high pass filters and low pass filters are fixed at their highest and lowest calibrations.
There is a readymade filter IC available to minimize the circuit. It includes one low pass and one high pass filter, and one op-amp for summing up the outputs of both the filters. The most popular 60hz notch-filter IC from Texas Instruments is UAF42.
A 50 Hz notch-filter can reject a 50 Hz signal by keeping the power of the movement almost intact. A 50 Hz notch-filter is needed when the 50 Hz band is necessary to be accurately rejected.
50 Hz notch filter circuit
A 50 hz circuit can be designed using the same frequency of a 60 hz notch-filter as given previously. Some typical values for creating a 50 Hz filter are given below. C= 47 nano-farad, Resistance R1, R2 = 10 kilo-ohm, R3, R4 = 68 kilo-ohm.
switched capacitor notch filter
A switched capacitor notch-filter is another advanced topology. This topology provides high precision, high Q value. This topology has several applications.
HF notch filter
HF Notch-Filter stands for High-Frequency Notch-Filters. Notch-filters of 50-60 Hz cannot give a good depth value or a high Q. High-frequency notch-filters (which rejects or allows a high-frequency component) are more realistic, provides a desired bandwidth and depth.
1khz notch filter
A one kilo-hertz notch-filter has a basic principle, the same as the previously discussed 50 hz or 60 hz filters. The only difference is that a one khz notch-filter is more realistic and can be designed for real-time applications. The 50-60 Hz filters are capable of giving 40 to 50 dB depth. But as an engineer, one must focus on the depth and the Q value. So, the one khz filter comes into action.
Notch filter in frequency domain
Notch-filters deal with frequency. The main principle of a notch-filter is to block a certain narrow band of frequency. So we can say the notch-filter works in the frequency domain only.
2 meter notch filter
A 2 meter notch-filter is a solution to a very general communication problem called – intermodulation. But the filter suffers a high loss during operation.
Audio notch filter
A notch-filter is an important instrument for audio engineering. Generally, some unwanted frequency components get mixed up in the original audio. To remove or eliminate such frequency, an audio notch-filter is used.
Notch filter equalizer
A notch-filter can be used as an equalizer in audio engineering. It can help to find out several unwanted spikes or noise, and also, it can remove those noise and spikes. That is how it helps to make the audio clear.
Periodic noise reduction using a notch filter
There is certain kind of periodic noises in digital images. The noises are repetitive and unwanted. They create certain patterns and affect the picture badly. One of the solutions to the problem is an optimum notch-filter.
At first, the noise frequency is determined, then the notch-filter produces the repetitive noise, and the output with lesser noise is produced.
Acoustic notch filter
As mentioned earlier, Notch-filters are important for audio engineering. After the audio is being recorded, different audio or acoustic audio is needed to mix up. There is a probability that any spike gets introduced in the mix-up. An acoustic notch-filter can remove such noise and spikes.
Variable notch filter
Variable notch-filters are essential for audio engineering. These kinds of notch-filters can change the intended frequency in a certain range.
In audio engineering, several unintended frequencies may present; to remove them, we need notch-filters. Instead of using one filter to omit a single frequency is not a great solution. Variable notch-filters serve our purpose here.
T Notch filter
T notch filter is a basic notch-filter with a ‘T’ network of RCR components. It is a special design technique.
Double T Notch filter | Double notch filter
Double T notch-filter or Twin T filter is an updated version of the T network. As the name suggests, here, two T networks are connected to form a notch-filter. One network consists of RCR components. Another is of CRC components.
Crossover notch filter
Crossover notch-filters can be described as series of notch-filters connected. These filters are designed so, to eliminate the driver resonance from the filter networks.
Series notch filter
Series notch-filters are used for the elimination of the driver resonance. Series notch-filters are designed using Capacitor, Resistance, and an Inductor. All the components are connected in a series connection, and the driver is connected in parallel with them.
Parallel notch filter
Parallel notch-filters are specially designed to eliminate significant unwanted peaks from the driver’s response. This filter is similar because all the basic elements are connected in parallel, unlike the series notch-filter.
High Q notch filter
High Q notch-filters are popular for providing great depth in rejection. Generally, Twin T notch-filters are used to get a high q value and get more depth—the Q value changes from normal 0.3 to 50 for a Twin T filter.
Sallen key notch filter
Sallen Key is a topology for designing higher-order filter circuits. Using this topology, notch-filters can also be created. The topology is also termed as Voltage Controlled Voltage Source. R.P. Sallen and E.P. Key first started it in the year 1955. Therefore, the topology is named after them.
Butterworth notch filter
Butterworth filters provide the flattest possible frequency response. So now, if a notch-filter is designed to provide a flat response, then the notch-filter will be called a Butterworth notch-filter.
AM Notch filter
AM Notch-Filter or Amplitude Modulation Notch-filter is designed to help the measurement of emission of a broadcasting station using a spectrum analyzer. AM Notch-filter is very useful for AM radio communication stations when there are nearby other towers. This is because it can allow only AM band EAS reception while the other strong fields are present.
Dynamic notch filter
The dynamic filter is a set of algorithms. First, the algorithm finds the noise frequencies. Then, active notch-filters are used to eliminate such spikes of noise.
Microstrip notch filter
As we can see, there are several filters available in the market for different uses. But Microstrip notch-filters are especially useful for wireless communication systems.
Analog notch filter
A notch-filter can be classified into the main domain; one is Analog another – Digital. We have previously discussed Digital Notch-filter, like – IIR, FIR, etc. Analog notch-filters are RLC notch-filters, RC notch-filters, T notch-filters, Twin T notch-filters, etc.
RC Notch filter
RC notch-filters are analog notch-filters that are designed with resistors and capacitors. In this kind of filter, manually, we can supply values of r and c.
IC Notch filter
LC notch-filters are analog notch-filters that are designed with an inductor and capacitor. In this kind of filter, manually, we can supply values of L and c.
Arduino Notch filter
Several digital filters can be designed using Arduino. Writing appropriate codes will help an engineer to realize even Notch-Filter digitally. The digital filter codes are available on GitHub. Try to modify them to make a notch-filter.
Coax stub Notch filter
Coax stub notch-filter is a type of notch-filter build within coaxial cables to remove noise and attenuation. ‘T’ coaxial connector will be very useful for designing such a filter. The addition of a second stub will be very helpful to improve the situation. Radio, Television centers use this filter.
FM broadcast notch filter
Almost in every major city, there is a high possibility that one can receive the radio frequency from the FM radio stations. The FM broadcast notch-filter will provide a 30db attenuation for the FM signals in the range of 88 to 108 MHz.
GPS Notch filter
GPS notch-filters help to catch the satellite signals. However, the basic rule is that the GPS module will receive a comparatively weaker signal from the satellite. This is because the nearby located towers may interfere with the incoming signal.
The GPS notch-filter will help here to attenuate the signal by – 30 dB. In addition, it will allow the GPS module to receive a fairer band from the satellite.
Bainter Notch filter
Bainter notch-filter is nothing but a basic notch-filter. A notch-filter consisting of one low pass filter, one high pass filter, and one adder to get the output frequency response can be termed a Bainter Notch-filter.
Wideband notch filter
If a band-reject filter has a wideband frequency as the operational band, then the filter is technically a wideband filter. If the band-reject filter has a narrow band of frequency, the filter is known as the Notch-filter. So, a Notch-filter cannot be a wideband notch-filter. It is technically impossible.
Eagle notch filter
A QAM notch-filter is based upon the phase cancellation concept. Eagle Comtronics Inc designs this narrow network. That is why QAM notch-filters are popular as Eagle Notch-Filter.
Crystal notch filter
Notch-Filters can be designed using crystals also. A crystal has a very high-Quality factor. A crystal notch-filter is useful for creating a notch-filter that has a very narrow band.
Peak notch filter
It is a digital notch-filter. The filter can resist each channel of an input signal for a certain center frequency and a bandwidth of 3 dB.
Narrow notch filter | Narrow band Notch filter
Notch-filters reject a very sharp band of frequency, saying a very narrow band of frequency. That is why notch-filters are often termed narrow notch-filters.
TV channel Notch filter | TV Notch filter | Cable Notch filter
The TV notch-filters help to solve the modulation problem that could occur in the transmission line. The tv notch-filter can make room for the modulated channel once it is installed in the queue. The filter also prevents reverse broadcasting to the coaxial cable. The increasing bandwidth now increased the demand for cable television notch-filters.
MNE Notch filter
MNE is popular software which provides us platform to build several electronics instrument. For example, we can design certain notch-filters in the MNE platform by writing some specific code.
Opposite of Notch filter
Notch-filters reject the very narrow bandwidth of signals and allow other components of that signal. The same but opposite task is performed by bandpass filters. The bandpass filters allow passing a certain band of frequency and block different parts of the signal.
Automatic Notch filter
An automatic notch-filter is something that can change the center frequency as well as the Q value as per the need. Several mechanical systems use these kinds of filters.
Gaussian Notch filter
A gaussian notch-filter is a digital filter. This filter is used to remove noise from various digital images. The specialty of the filter made it popular and is used in multiple applications as well as in various investigating agencies.
Notch filter parameters
There are some parameters to measure the accuracy of the notch-filter. One of the important among them is the Q factor or Q (Details given above). Another is the depth of the output. Finally, the bandwidth is also one of the parameters.
Notch filter impulse response
The following image shows a notch-filter impulse response.
Second order Notch filter transfer function
The following expression shows the second order notch-filter’s transfer function.
Before discussing about circuits of notch filter, let us find out the definition of notch filter. A notch filter can be defined as a band stop that has a very narrow frequency bandwidth. Great depth, high-quality factor, and sharpness in band-reject characterize a notch filter. There are several kinds of notch filters which we will discuss letter.
what does a notch filter do?
A notch filter does the work of a band-stop filter in a more specified way. As the band reject filter rejects the given band of frequency from the main signal, the notch filter does the same. But, for a notch filter, the band of frequency is much narrower. Notch filter basically attenuates the given band of frequency which is the exact opposite of a band pass filter where a certain band of frequency is allowed while the other bands are rejected.
notch filter vs low pass
Let us discuss some differences between a notch filter and a low pass filter. It will also help to understand the difference between a band pass filter and band reject filter.
Points of Discussion
Low Pass Filter
Notch Filter
1. Passing Frequency Band
Only Low-frequency components are allowed to pass. (Certain limits are set previously)
All frequency except a narrow band gets passed.
2. Blocking frequency
High-frequency filters are blocked.
The narrow, specified frequency band is blocked.
3. Bandwidth
Comparatively wider band is passed.
A comparatively narrower band is rejected.
Notch Filter Circuit Table – 1
Notch Filter Block Diagram
Notch filter is a combinational circuit of Low pass Filter and High Pass Filter. The block diagram given below depicts the basic concept of a notch filter.
Notch Filter Circuit: Block Diagram
rlc notch filter
In general, most of the Notch filters are designed using three basic components. They are – Resistance, Capacitance, and Inductor. Therefore, if any notch filter is developed using these elements, that notch filter can be termed RLC Notch Filter. Almost all RLC filters are passive filters as they does not contain any active element like operational amplifier. For that, these filters also deprived of the amplification process.
Here is a circuit diagram of notch filter. It is a circuit of active notch filter, as we can see operational amplifiers are used. We can also see, the circuit is combination of both low pass filter as well as high pass filter. The summing amplifier sumps up the output from the low pass filter and high pass filter. It also provides amplification of the signal.
Notch Filter Circuit
notch filter schematic
The Notch filter circuit is a very simple and easy-to-understand circuit. The only complex part of the circuit is the op-amp. Check out my article on operational amplifiers to get the schematic diagram of an operational amplifier.
notch filter cutoff frequency
The cutoff frequency is the parameter using which one can analyze a filter. In general, the cutoff frequency of a notch filter refers to the frequency of the narrowband which needs to be blocked through the filter. It is an important parameter for designing the notch filter circuit.
The HF cut-off of the LPF: fL = 1 / ( 2 * RLP * CLP * π)
The LF cut-off of the HPF: fH = 1 / ( 2 * RHP * CHP * π)
notch filter bandwidth || bandwidth of notch filter
Notch filters have very narrow bandwidth. Also, it is the reason why a notch filter is made out of a band-reject filter. The sharpness is depended on the Q of the notch. Normal band reject filter has a wider bandwidth than the notch filter. It is another important parameter for designing the filter. Bandwidth is also associated with the performance parameter of the filter.
Bode plot of a filter refers to the graphical representation of frequency response. Let us find out the response of a notch filter. The following plot describes the depth, bandwidth of a signal after it passes through a notch filter. It is an important parameter to determine the accuracy of the notch filter.
Notch Filter Circuit 2: Frequency Response
lc notch filter design
A notch filter can be designed using inductor and capacitor also. It will be a passive filter as it has no active component like operational amplifiers. The design procedure is given in the notch filter design article. Check it out here. The notch filter circuit diagram is given below.
Notch Filter Circuit 3: LC Notch
notch filter ic
Notch filter can be designed inside an Integrated Circuit. There are plenty of ICs available in market which functions like notch filter. One of the commonly used IC is the LTC1059. The pin diagram of the IC is given below.
As the name suggest, a 60 Hz filter attenuates 60 Hz of frequency. The filtering is done using a notch filter because notch filter provides a sharp depth. 60 Hz filters are so popular because it is the supply frequency of USA. Other countries like India has a frequency supply frequency of 50 Hz. That is why 50 Hz filters are also used to remove supply interference. These types of filters are mainly used in ECG, EEG machines (the details are given in the Notch filter Design article).
60hz notch filter circuit
The 60 Hz notch filter is designed using several op amp. Some of them are to realise the Low pass filter, some of them to realise the high pass filter. The IC UAF42 is used to get rid of such complicated circuit. The value of registers and capacitors are given within the circuit diagram. While designing the circuit, make sure you use the exact value of the resistor and capacitors to get a more accurate result. The 60 hz notch filter circuit is given below.
60 Hz Notch Filter Circuit
rf notch filter circuit
Radio Frequency notch filter has several applications. The circuit is designed using the inductors and capacitors only. At first, one capacitor and one inductor is placed in parallel. Then a set of capacitor and inductor are placed in series with the previous connection. Then another pair of inductor and capacitor (Values are equal to the first used set) are placed in parallel, in series with the second connection. The circuit is given below.
Audio notch filter is a very important filter for audio engineering. Notch filters removes the spike and noises to make the audio better. The circuit diagram of a basic audio notch filter is given below. As we can see, the circuit can be designed using passive elements like – resistors and capacitors. The generalised values of them are also given. As the circuit is passive one, there is no amplification part.
Audio Notch Filter Circuit
audio notch filter schematic
A schematic diagram is something which is represented by basic elements. The audio notch filter has quite a simple design. As we can see in the circuit, it is already drawn with basic elements. You can still try to simplify the circuit.
digital notch filter transfer function
Transfer function is an important expression in control system engineering. It is referred as the mathematical expression which provides output for every set of input. The following expression gives the transfer function of a digital notch filter –
Different Types of Notch Filters
low pass notch filter
Notch filters are made up of both high pass and low pass filters. Low pass filters allow the lower frequency band of a signal. Notch filters allow a narrow band of frequency resisting other bands. If the wz< wp, it is common to pass notch type. (Check the transfer function derivation in the other article to understand).
high pass notch filter
As mentioned earlier, Notch filters come with both the high pass and low pass filters. High pass filters allow the higher frequency band of a signal. A notch filter can allow any narrow band of the signal. So, if a notch filter is designed to pass a narrow band of the high-frequency component, then the filter can be said a high pass notch filter. If the wz> wp, it is a high pass notch type. (Check the transfer function derivation in the other article to understand).
2.4 ghz notch filter
We have seen notch filters are useful in minimizing interferences. Radar systems use a wide range of signals. These signals are transmitted towards various places from the air. Now, there are several electronics equipment and appliances which work on different frequency levels. Therefore, there is a high probability that the signals might get interfered among each other.
A 2.4 GHz is designed to omit or eliminate such kinds of interferences and provide a smoother service.
quarter wave stub notch filter
Quarter wave stub has several applications. If a quarter wave stub is left with an open end, it can be used as a notch filter, attenuating a certain frequency band. That is how the purpose of a notch filter is served. It is one of the important types of filter for research and development purpose. It has several other applications also.
optical notch filter
There are also notch filters in Optics. Unlike an electronics notch filter, the optical notch filter blocks a specific wavelength of light and allows the other wavelength to pass smoothly. As notch filters work for narrow bandwidth, the optical notch filter can have 10 nm. Optical notch has a lot of variety. The applications depends on the need of the notch filter.
532 notch filter || 532 nm notch filter
532 notch filter represents 532 nm optical notch filter. This optical filter is named so because it can block the light component of 532 nm wavelength and allow all other wavelengths. These filters have applications in scientific researches.
785 nm notch filter
785 notch filter represents 785 nm optical notch filter. This optical filter is named so because it can block the light component of 785 nm wavelength and allow all other wavelengths. Just like 53nm optical notch, it has also applications in scientific researches and applications.
multi notch filter
Multi-notch filters are a kind of variable notch filter for optics. In optics, notch filters are also used where we can eliminate a certain wavelength. A multi-notch filter can block multiple wavelengths at once.
holographic notch filter
A holographic Notch Filter or HNF is one type of optical notch filter. These kinds of filters can give a high laser attenuation for narrower bandwidth. HNF has application in Laser Spectroscopy.
laser notch filter
As one can guess, Laser Notch Filter is a kind of Optical Notch Filter. Laser filters are used to block a certain wavelength of laser light. There is various kind of laser notch filter available in the market. They are useful for laser-based Raman devices and Biomedical systems.
notch filter raman spectroscopy
Let us understand what Raman spectroscopy is. It is a chemical analysis that can provide us very detailed info on chemical structure. Raman spectroscopy comes into the picture when there is an interaction of light with any chemical particle.
To realize Raman Spectroscopy, a light source is needed as well as a spectrometer. Now, light is emitted from the start and caught in the spectrometer. To remove the unwanted lights, the optical notch filter is used.
2nd order notch filter || second order notch filter
In general, a filter is called a second-order filter when it has one more RC network along with a first-order network. A notch filter is a 2nd order filter as it comes with a low pass filter and a cascaded connection of a high pass filter. 2nd order notch filter has cut-off frequencies. Sallen Key feature topology is used to make higher
fliege notch filter
Fliege notch filter is another notch filter topology. There are several advantages of this topology over the twin T notch filter. First, the center frequency can be tuned using only the four precision components, i.e., two resistors and two capacitors.
One of the great features of the topology is that if there any slight mismatch, the center frequency gets affected, but the depth of the filter remains the same.
The Q of the filter can also be adjusted using two independent resistors.
fpv notch filter
These refer to 433/1.3 GHz notch filters which can filter out interference in the 1.2- 1.3 GHz frequency band if the filter is used in the 433 MHZ RC transmitter.
dc notch filter
There are several dc notches filters available. One of the most widely used applications is the GPS notch filter. The notch filter helps to eliminate interference and receive the satellite signal.
helical notch filter
Let us know what a helical filter is. A helical filter is made of a series of cavities that are further magnetically coupled. These filters provide a high Q and great performance.
Now a Helical filter can be turned into a notch filter if one of the taps of the helix is being attached to the transmission line. The depth of the notch filter will be around thirty to forty dB.
tinnitus notch filter
At first, let us know what Tinnitus is. Tinnitus is a hearing problem. If one experiences a buzzing or ringing noise in one or both o his/her ear(s), then the syndrome is called Tinnitus.
As a remedy to it, conventional hearing aids are suggested by doctors. But it is recently observed that if a notch filter is added for the tinnitus frequency, the mechanism will improve and help the recovery process.
bridged t notch filter
A bridged t notch filter is quite a different type of filter. The filter provides a shallow depth and also comes with a frequency band that is wider than the available notch filter. It is used where a need for equalization is there. It is also not considered an active filter.
microwave notch filter
A dual-drive Mach-Zander modulator achieves a microwave Notch Filter. It is efficient, and the frequency can be adjusted. Therefore, it has a higher value of the frequency band.
A notch filter is generally a modified form of the Band Reject or Band Stop filter. The main objective of these filters is to stop or prohibit a certain range of frequencies from appearing in the output. For example, a Band Stop filter having a narrow stopband is called a notch filter.
Let us take an example. Suppose a Notch filter is designed to stop frequency between 100kHz to 110kHz. So, it will pass every signal below the 100kHz range and give any signal higher than 110kHz but will prevent any signal in between the 100kHz to 110 kHz.
how to build a notch filter
The building of a notch filter is quite easy. There are three main steps in building a notch filter. The steps are – 1. Note down the requirement perfectly, 2. Understand the need and design the notch filter (Designing a notch filter is written below), 3. Check with the expectation. (If perfect, then use, if not re-design the filter).
notch filter eq || notch filter equation
Some of the important equations of notch filter are given below.
The HF cut-off of the LPF: fL = 1 / ( 2 * RLP * CLP * π)
The LF cut-off of the HPF: fH = 1 / ( 2 * RHP * CHP * π)
The quality factor of the notch filter: Q = fr / Band Width
notch filter ic
There are several Integrated Circuit available in the market which implement a notch filter. There are many advantages of using IC over conventional circuits. One of the most popular normal notch filter IC is LTC1059. The PIN diagram of the IC is given below.
The q factor of a notch filter is the same as the q of a notch. Q or Quality Factor of a Notch filter is given by the following equation: Centre Frequency/Bandwidth. Q is the measurement of the selectivity of the filter. It also gives an idea of sharpness of the depth.
The center frequency is the Notch Frequency, and it is the center frequency of the passband.
notch filter frequency
The frequency of the notch filter is referred to as the frequency of the stopband. This is because the narrow band’s frequency is what the notch filter rejects. Therefore, the frequency is also the identity of the notch filter.
notch filter example
There are several examples of notch filters. There are numbers of types also. Every types has sub topics as well as many examples. Digital notch filters, analog notch filters, optical notch filters, FM notch filters, audio notch filters, helical notch filters, tunable notch filters, 50hz notch filters, and 60 Hz 2.4 GHz notch filters. Some of the examples are based on their specifications. Like – 532 nm notch filter. It is a optical filter te blocking wavelength is specified with the name.
Notch filter design || rlc notch filter design || how to design a notch filter
Let us design a notch filter from scratch. First, let us create an RLC type filter(notch) to eliminate the band of 45 kHz to 50 kHz. Say, the inductance is L = 30 mH.
So, the given datas are: fL = 45 kHz, fH = 50 kHz, l = 30 mH = 0.03 H
The resonant frequency will be: fr = fH – (BW/2)
The BW is Bandwidth and BW = 50 – 45 = 5kHz.
Or, fr = 50 *103 – ((5 * 103)/2)
Or, fr = 50000 – 2500
Or, fr = 47.5 * 103
So, the Resonant frequency is 47.5 kHz.
Now, we know that resonant frequency can be written as –
fr = 1 / [2 * pi * (LC)1/2]
or, 47.5 * 103 = 1 / (1.088 * C1/2)
or, C = 374.41 pico-Henry
So the Quality factor will be = fr / BW = 47500/5000 = 9.5
Again, Q = wr L / R
Or. R = wrL/Q = 2 * pi * f * L/Q
Or, R = 8.95 kilo-ohm
So for the notch filter, R = 8.95 kilo-ohm, L = 30 mH, C = 374.41 pico-farad.
tunable notch filter
Tunable notch-filters are such narrowband filters where we can manually get the high rejection from a particular frequency and comparatively lower attenuation from other frequency signals. There are several tunable notch-filters available in the market, like – EM-7843. Tunable filters can be of another type. If the Q factor of a notch filter is tuneable that filter can also be termed as tuneable notch filter.
tunable notch filter design
The design of the Tuneable notch filter is not so simple. It requires a lot of calculation and concept. But the creation of a digital tuneable notch filter is somewhat easy. The design should be made such that one can change the centre frequency easily.
digital notch filter
Digital notch filters refer to the FIR Notch-filter and IIR Notch-Filter. FIR and IIR both have their advantages in different conditions and are used as per the requirement. They are termed digital because they are designed digitally.
digital notch filter design
Digital notch filters have two types of design techniques. They are – Infinite Impulse Response Notch Filter (IIR), Finite Impulse Response Notch Filter (FIR). We have discussed both the filter details below.
dsp notch filter
DSP stands for Digital Signal Processing. The notch filters used in the digital processing of signals are termed DSP notch filters. Therefore, it is fairly understandable that only digital filters are used as DSP notch filters. The FIR, IIR notch filters are an example of these kinds of filters.
design of notch filter in dsp
Digital notch filters have two types of design techniques. They are – Infinite Impulse Response Notch Filter(IIR), Finite Impulse Response Notch Filter. We have discussed both the filter details below.
fir notch filter
FIR filters stand for Finite Impulse Response filter. FIR filters generally come with lots of stability, which made them famous. When the stability of the system is more necessary, then these types of filters are used.
fir notch filter design
There are several methods of designing an FIR notch-filter, like – frequency sampling and computer optimization. Analytical methods, Semi-Analytical methods, second-order IIR filter prototypes are some other processes of preparing the same. Bernstein polynomials are also used in creating the FIR type digital notch filters.
iir notch filter || digital iir notch filter
IIR stands for Infinite Impulse Response. This is also a digital filter like an FIR filter. IIR filters generally come with an efficient approximation for a very low order requirement. These types of filters are required when the linearity of phases is not that much important.
iir notch filter design
IIR notch filters are designed in two major parts. At first, an analog notch filter is designed with the required specifications, and then the analog filter is transformed into a Digital IIR filter using inverse transformation.
active notch filter design || analog notch filter design || notch filter derivation
Let us design a notch-filter from scratch. First, let us create an RLC type filter(notch) to eliminate the band of 55 kHz to 60 kHz. Say, the inductance is L = 30 mH.
So, the given datas are: fL = 55 kHz, fH = 60 kHz, l = 30 mH = 0.03 H
The resonant frequency will be: fr = fH – (BW/2)
The BW is Bandwidth and BW = 60 – 55 = 5kHz.
Or, fr = 60 *103 – ((5 * 103)/2)
Or, fr = 60000 – 2500
Or, fr = 57.5 * 103
So, the Resonant frequency is 57.5 kHz.
Now, we know that resonant frequency can be written as –
fr = 1 / [2 * pi * (LC)1/2]
or, 57.5 * 103 = 1 / (1.088 * C1/2)
or, C = 255 .51 pico-Henry
So the Quality factor will be = fr / BW = 57500/5000 = 11.5
Again, Q = wr L / R
Or. R = wrL/Q = 2 * pi * f * L/Q
Or, R = 7.39 kilo-ohm
So for the notch-filter, R = 7.39 kilo-ohm, L = 30 mH, C = 255.51 pico-farad.
lc notch filter design
As we can interpret from the name of the filter, the LC Notch-filter is designed using only inductors and capacitors. The design method of an LC notch-filter is quite simple. At first, one inductor and once capacitor is kept at parallel connection. Then another combo of inductor and capacitor is kept in series connection. The circuit diagram is as follows.
LC circuit for notch-filter
The output impedance comes as:
The transfer function is:
The cut-off frequencies are –
notch filter using op amp || notch filter circuit using op amp
Notch filters are realized using operational amplifiers. At first, both the high pass and low pass filters are created using operational amplifiers. Then their outputs are summed up using another operational amplifier to get the outcome. The circuit diagram given in the article depicts a notch filter using op-amps.
60hz notch filter
A 60 Hz notch filter can reject a 60 Hz signal by keeping the power of the movement almost intact. A notch filter is used because it will accurately attenuate the frequency band. A 60 Hz notch filter has demand in the USA because the power supply in households has a frequency of 60 HZ.
60 hz notch filter design
As we know, any notch filter is designed with a high pass filter and a low pass filter. An additional op-amp is needed to add up the output of both the filters. Typically, the Q comes as 6 for a 60 Hz filter. The given equation can determine the notch frequency.
ALP is the low pass filter’s output when the frequency of the filter is the same as the desired output frequency, whereas AHP is the output for the high pass filter. In general, the
value is one. So, the notch frequency comes as output frequency, which is 60 Hz.
The following expression can also determine the output frequency:
As we can observe, the output frequency is dependent on the RF. So, changing the value of Rf will change the notch frequency.
rf notch filter design
Designing an RF filter is a very complicated process. It needs a skilled engineer as accuracy is an important parameter for these kind of filters. The design process of an RF notch filter is given below.
Specify the Response: In his stage, all the required parameter value is specified. Parameters like – Response, cut-off point, etc. are needed to be set.
Frequency Normalization: The frequencies are converted to match the standard tables and charts.
Calculation of Ripple: In this stage, the concept of a notch filter is used. To create an RF notch filter, which can reject only one frequency from a certain frequency band, the ripple value should be considered a high priority. The higher the ripple value tolerance limit, the more selective the filter becomes.
Matching the attenuating curves.
Calculation of element values.
Scaling of normalized values.
programmable notch filter
The most popular filter used nowadays is the Programmable filter. Programmable filters are easy to maintain, easy to work with. Programmable notch filters are no exception. We can control the Q value as well as the natural frequency by just changing the clock frequency.
notch filter code
The notch filter code to design a notch filter in MATLAB is given below. Writing any one of them with the right specifications will provide you a notch filter.
Code for designing a notch-filter in MATLAB simulator.
fm broadcast notch filter
Almost in every major city, there is a high possibility that one can receive the radio frequency from the FM radio stations. The FM broadcast notch filter will provide a 30db attenuation for the FM signals in the range of 88 to 108 MHz.
audio notch filter
A notch filter is an important instrument for audio engineering. Generally, some unwanted frequency components get mixed up in the original audio. To remove or eliminate such frequency, an audio notch filter is used.
The following circuit is an example of audio and fm notch design. Carefully observe the resistance and capacitor values before starting the design. The formula for centre frequency is also given.
Audio notch-filter design circuit
audio notch filter schematic
The audio notch filter has quite a simple design. The schematic can be drawn easily for the current condition by following the standard procedures.
biquad notch filter
A biquad filter is a digital filter. More specifically, it is an IIR filter that has two poles and two zeros. The ‘Biquad’ is an abbreviation from the term – Bi-quadratic. Notch filters can also be designed using the topology. The transfer function for the filter comes as:
532 nm notch filter
532 nm notch filter is a variety of optical notch filters. The specification of the filter is 532 nm, that means the optical notch is able to block the light component having wavelength of 532 nanometre. It is one of the most popular optical notch filter. There are other specifications like 785 nm.
harmonic notch filter
A harmonic notch filter is a special type of notch filter, which has applications in several fields. The filter follows the following transfer function.
H(z)=12(1+A(z))
notch filter design tool
There is a different kind of tools available in the market for designing the notch filter digitally. Many types of digital filters can be created using such devices. It would be best if you assigned the frequency value only. One of the favourite tools is produced by Texas Instruments.
betaflight notch filter
Betaflight is a flight control software where multi-rotor crafts are controlled. As a part of the process, notch filters are also designed and tuned in the software.
Here, wz refers to the Zero-Circular Frequency, whereas wp refers to the pole-circular frequency. Finally, q means the Quality Factor of the notch filter.
Q is given by – fr / Bandwidth.
If the ωp = ωz, it is a standard notch type.
If the ωp > ωz, it is a high pass notch type.
If the ωz < ωp, it is a low pass notch type.
notch filter for ecg signal
ECG or Electrocardiograph is a very important process of diagnosis in medical sciences. Several filters are used to display the output data produced by the machine. Without the filters, it is quite impossible to read the values.
There are three kinds of filters used in an ECG reading. They are – high pass filter, low pass filter, and notch filter. High pass filter filters out high-frequency components, whereas low pass filters do the same for common frequency components. The notch filters filter out a certain given range of frequency.
Especially the supplied frequency of the AC interferes with the ECG readings. Notch filter removes such interference. For North America, the supply frequency is 60 Hz, so a 60 Hz notch filter is used. In India and other countries where the supply frequency is 50 Hz, a 50 Hz notch filter is used.
The op-amp diagram marks the inputs, outputs, and saturation voltage connections. It is an open-loop system. The below image represents an op-amp diagram.
In-general typical op-amp ICs have eight pins. Seven are functional, while one pin is dedicated for output. It takes four inputs; 2 of them are for inverting terminal and non-inverting terminal, and the rest 2 are for positive and negative saturation voltage. The pinout of IC741 is given above.
Op amp schematic
The below image gives a schematic view of an op-amp.
As we can see in the image, an op-amp consists of transistors and resistors. The input impedance is high because of the Darlington pair of the NPN transistors. There are two differential gain stages, and the output is taken from the single-ended emitter follower. The transistors T1 and T2 are identical, and so as the T3 and T4.
Types and Applications
Op amp applications | Op amp uses
Op-amps are one of the essential elements for circuit designing in electronics. They are used in various places. Some of the examples are –
Unity gain buffer, phase shift oscillator, current to voltage follower, the voltage to a current follower, summing amplifier, integrator, differentiator, half-wave rectifier, peak detector, etc. There are many more applications of the op-amp. Almost every electronic gadget is incorporated with an op-amp.
High pass filter op amp
A high pass filter can be built using an RC filter circuit and a typical op-amp. Combining a passive RC filter with op-amp functions like an active high pass filter. The inverting or non-inverting terminal operation of the op amp is required for the circuit. The below image represents a high pass filter op amp circuit.
Op amp bandpass filter
A bandpass filter allows a signal of the specified frequency range only. This filter filters out other components of frequencies. Op-amps are used to make such types of filters. The circuit is designed by cascading a high pass filter with an op-amp and then a low pass filter.
Subtractor op amp
Subtractor op-amp amplifies the difference between the two input voltages and provides that as output. It performs the subtraction operation, unlike a summing amplifier which adds up the input voltages. That is why it is known as subtractor op-amp.
Op amp adder
Op-amp adder or summing amplifier is the amplifier that amplifies the summation of the input voltages and provides as output. It performs summation or addition operation, unlike a differential amplifier which performs subtraction operations. The circuit diagram is given above.
Unity Gain op amp
A unity gain op-amp or a voltage follower circuit, or a buffer circuit is a specially designed non-inverting amplifier model. Observe the circuit of the non-inverting amplifier given above. If we made the feedback resistance zero and the inverting terminal infinite resistance, the amplifier’s gain would be unity. That is why this circuit is known as unity gain op-amp or unity gain buffer. This buffer is used for impedance matching.
Op amp oscillator
It is also possible to create an oscillator using an op-amp. The below-given image represents the circuit diagram of a phase shift RC oscillator.
After some general calculations, we have found out that oscillation frequency is f = 1/ (2πRC -/6) and the voltage gain Av = -29 for sustained oscillation.
Audio op amp
Operational amplifiers are heavily used in audio processing and audio mixers. An op-amp can amplify weak voice signals. Several types of audio op-amps are available in the market. Some of them are – LT1115, UA741, etc.
Op amp level shifter
In a single supply op-amp, the op-amp can level shift a ground-referenced signal. A level shifter can translate logic signals from one level to another. Sometimes there is a need for converting a positive to negative signal into an acceptable range for a single supply analog to digital converter.
Op amp voltage divider
Op-amps are also used as a voltage divider. Op-amp is used to make voltage dividers as using op-amp can increase the system’s gain.
Single supply op amp
Single supply op amp is such a special op-amp with only one supply terminal. The supply terminal is typically the +Vcc. So, the output lies between the range of +Vcc and the ground (GND) for an input signal.
High Voltage op amp
A high voltage amplifier is typically used to amplify the input signal to a high voltage output signal. It can provide the power gain at the voltage and current combinations. Some of the high voltage op-amps applications are – inkjet printers, ultrasound transducer, Geiger counters, biomedical tests, etc.
It is another integrated circuit that operates op-amp. It is a high-performance eight-pin IC that doesn’t need any external frequency compensator components. Some of the other models are – CF158MT, AN45588, LA6458, etc.
lm358 op amp
lm358 is another type of IC that consists of a couple of op-amps. It is a low-power IC, which National Semiconductor first developed.
ua741 op amp
This is another type of IC that includes an operational amplifier. It has eight pins. The maximum supply voltage is +18V, and the maximum differential input voltage is +15V. The CMMR is 90 dB. UA 741 is used in audio applications, music players.
Lm324 op amp
Lm324 is a specially built IC, which can function as an amplifier, comparator, rectifier, etc. This IC has 14 pins, representing four op-amps. It has a wide bandwidth of around 1 MHz and a gain of 100 dB. They are applied in various fields of robotics, oscillators, etc.
Ne5532 op amp
Another IC of the op-amp is ne5532. It is a high-performance amplifier that has excellent DC and AC voltages. It has low noise, maximum output swing bandwidth, and a high slew rate. Different variations of this type of ICs are – NE5532A, SA55332, etc.
Important Parameters, Rules, Equations
Op amp circuit analysis
The op-amp circuit analysis reveals the functionality of each part of an op-amp and how they are connected or interconnected to provide the output path. Circuit analysis of op-amp can be classified into two types –
The open-loop circuit analysis analyzes the system without the feedback system, and the closed-loop circuit analysis is the analysis of a circuit with a feedback system.
The concept of virtual ground, high input impedance, and infinite gain are necessary for the op-amp circuit analysis.
Op amp golden rules
One op-amp designer should always keep in mind some essential rules. They are –
Op amp provides infinite gain.
The input impedances are high.
No current flows through the op-amp at the beginning.
The offset voltage is adjusted to make it zero.
Op amp formulas
There are no hard and fast formulas for the op-amp. There are several types of op-amps, and they have their specific equations and formulas. Like – formulas for output of Non inverting op amp: V0 = [ 1 + (Rf/R1)] * Vin and formulas for output of Inverting op amp: V0 = – (Rf/R1) * Vin
Input impedance of op amp
The input impedance is high because of the Darlington pair of the NPN transistors. For an ideal op-amp, the input impedance is infinite. Due to the high input impedance, we can assume that the current flows through the feedback at the beginning stage. Typically, the values are in between 1 megaohm to 10 tera ohms.
Output impedance of an op amp
Output impedance of op-amp referrers to the impedance provided by an op-amp at the output stage. An ideal has an output impedance of 0 ohms. The output driver circuit causes the output impedance of an op-amp.
Open loop gain of op amp
Open loop gain of an op-amp is the device’s gain when there is no feedback associated with it. For an ideal op-amp, the open-loop gain is infinite. A typical open-loop gain of the typical op-amp is around 100 dB.
Op amp offset voltage
An op-amp’s offset voltage is defined as the differential DC voltage between the input terminals. For an ideal op-amp, the offset voltage is zero. But for the practical op-amp, the external voltage is given to the op-amp.
Slew rate of op amp
Slew rate of the op-amp is the rate of change of the output signal if there is a step-change in the input signal. It is a parameter for the measurement of performance. The unit of slew rate is V/ ms. For an ideal op-amp, the slew rate is zero. It means that the input change will be reflected immediately in the output. For a typical practical op-amp, the slew rate value is 10 V / μs.
Op amp bandwidth
The bandwidth of an amplifier is referred to as the range of frequency above which the gain of the amplifier is higher than 3 dB. For a 741 MHz amplifier, the closed-loop amplifier is 1 MHz.
Op amp current source
An external current source with an op-amp provides a load resistance independent current. And as we have previously grounded the circuit, there is no chance of exposing two connections.
Op amp transfer functions
It is possible to obtain transfer functions of op-amp if the op-amps are represented in a classical feedback block diagram. Using the process of superposition, the transfer function can be obtained. The transfer function for the non-inverting terminal can be written as R1 / (R1 +Rf).
Op amp saturation
There is two input terminals, which takes positive and negative saturation voltages. Now, when an op-amp is in saturation, it means that the op-amp’s output is any of the saturation voltage provided from the supply.
How does an op amp work?
An op-amp typically goes through three stages of operations. The first one – differential input stage with higher input impedance, the gain stage in the second stage, and the push-pull output stage of lower output impedance.
What does an op amp do?
An op-amp or operational amplifier is an electronics device that performs certain mathematical operations and amplifies the input signal.
Introduction to Magnetic Microwave | What is Magnetron?
A magnetron is a kind of Microwave Tube. Before discussing magnetron and its related topics, let us find out some of the basic definitions.
Microwave Tubes:Microwave tubes are devices which generate microwaves. They are the electron guns which produces linear beam tubes.
Now, the definition of Magnetron is given as –
Magnetron:Magnetron is a type of vacuum tube which generates signals of the microwave frequency range, with the help of interactions of a magnetic field and electron beams.
Magnetron tube consumes high-power, and its frequency depends on the physical dimension of the tubes’ cavities. There is a primary difference between a Magnetron and other types of Microwave Tubes. A magnetron works only as an Oscillator but not an amplifier, but a Klystron (a Microwave Tube) can work as an amplifier and as an Oscillator.
The Siemens Corporation developed the very first magnetron in the year 1910 with the guidance from scientist Hans Gerdien. Swiss physicist Heinrich Greinacher finds out the idea of electrons’ motion in the crossed electric and magnetic field from his own failed experiments of calculation of the mass of electrons. He developed the mathematical model around the year 1912.
In the United States, Albert Hull started working to control electrons’ motions using a magnetic field rather than using the conventional electrostatic field. The experiment was initiated to bypass the patent of ‘triode’ of Western’s Electric.
Hull developed a device almost like a Magnetron, but it had no intention to generate signals of microwave frequencies. Czech physicist August Žáček and German physicist Erich Habann independently discovered that Magnetron could generate signals having frequencies of Microwave range.
The invention and increased popularity of RADAR increased the demand for devices which can produce microwave at shorter wavelengths.
In the year 1940, Sir John Randall and Harry Boot of University of Birmingham developed a working prototype of a cavity magnetron. In the beginning, the device produced around 400 Watts of power. Further development like water cooling and several other improvements hiked the produced power from 400 W to 1 kW and then up to 25 kW.
There was a problem related to the frequency instability in the magnetron developed by British scientists. In 1941, James Sayers solved that problem.
The cavity magnetron developed by Sir John Randall and Harry Boot of University of Birmingham, Magnetron Microwave, Image Credit: Elektrik Fanne, R&B Magnetron, CC BY-SA 4.0
Applications of Magnetron
A magnetron is a beneficial device, has several applications in various fields. Let us discuss some of them.
Magnetrons in Radar:The use of Magnetron for a Radar used to generate short pulses of high-power Microwave frequencies. A magnetron’s waveguide is attached with any of the antennae inside a Radar.
There are several factors of Magnetron which causes complexity to the Radar. One of them is the problem related to the frequency instability. This factor generates the problem of frequency shifts.
The second characteristics are that a magnetron produces signals with the power of broader bandwidth. So, the receiver should have a broader bandwidth to accept them. Now, having a wider bandwidth, the receiver also receives some sort of noise which is not desired.
An early commercial radar for airport, Magnetron Microwave, Image by: Unknown authorUnknown author, Magnetron radar assembly 1947, marked as public domain, more details on Wikimedia Commons
Magnetron Heating | Magnetron Microwave Ovens: Magnetrons are used to generate microwaves that are further used for heating. Inside a microwave oven, at first, the magnetron produces the microwave signals. Then, the waveguide transmits the signals to an RF transparent port into the food chamber. The chamber is of a fixed dimension, and also close to the magnetron. That is why standing wave patterns are randomized by the revolving motor, which rotates the food inside the chamber.
Magnetron Lighting: There are plenty of devices available which lights up using the Magnetron excitation. Devices like the sulfur lamp is a prime example of such light. Inside the devices, magnetron generates the microwave field, which is carried out by a waveguide. Then the signal is passed through the light-emitting cavity. These types of devices are complex. Nowadays, they are not used instead of more superficial elements like Gallium Nitride (GaN), or HEMTs are used.
Construction of Magnetron
In this section, we will discuss the physical construction and components of a Magnetron.
The magnetron is grouped as a diode as it is deployed on grid. The anode of the magnetron is set into a cylindrical shaped block which is made up of copper. There are filaments with filament lead and the cathode at the centre of the tube—the filaments-leads help keep the cathode and filament attached with it at the centre. The cathode is made up of high-emission material, and it is heated for the operation.
A Magnetron with its parts, Magnetron Microwave, Image Credit: HCRS Home Labor Page, Magnetron2, CC BY-SA 2.0 AT
The tube has 8 to 20 resonant cavities which are cylindrical holes around its circumference. The internal structure is divided into several parts: the number of cavities present in the tube. The division of tube is done by the narrow slots connecting the cavities to the centre.
Each cavity functions like a parallel resonant circuit where the anode copper block’s far-wall works as an inductor. The vane tip region is considered the capacitor. Now, the resonant frequency of the circuit is dependent on the physical dimensions of the resonator circuit.
It is evident that if a resonant cavity starts oscillation, it excites other resonant cavities and they start oscillation too. But there is one property that every cavity follows. If a cavity starts oscillation, the next cavity starts oscillation with 180 degrees delay in phase. This applies to every cavity. Now, the series of oscillation creates a slow-wave structure which is self-contained. That is why this type of Magnetron construction is also known as “Multi-Cavity Travelling Wave Magnetron”.
The cathode supplies the electrons necessary for the energy transfer mechanism. As mentioned earlier, the cathode is in the centre of the tube, further set up by the filament leads. There is a particular open space between the cathode and anode which needs to be maintained; otherwise, it will cause malfunction to the device.
There are four types of cavity arrangement available. They are –
Slot-type
Vane-type
Rising Sun type
Hole and slot type
Operation of a Magnetron Microwave
Magnetron goes under some phases to generate signals of microwave frequency ranges. The phases are listed below.
Though the name of the phases is indicative enough to let us discuss the incidents, those occur in each phase.
Phase 1: Electron Beam generation and acceleration
The cathode inside the cavity posses the negative polarity of the voltage. The anode is kept in a radial direction from the cathode. Now, indirect heating of cathode causes the flow of electron towards the anode. At the time of generation, there is no magnetic field present in the cavity. But after the generation of the electron, a weak magnetic field bends the path of the electrons. The path of the electron gets a sharp bend if the strength of the magnetic field increases further. Now, if the velocity of the electrons gets increased, the bend becomes sharper again.
Phase 2: Velocity control and changes of Electron beam
This phase occurs inside the ac field of the cavity. The AC field is located from adjacent anode segments to the cathode region. This field accelerates the flow of the electron beam, which is flowing towards the anode segments. The electrons which flow toward the segments gets slowed down.
Phase 3: Generation of “Space Charge Wheel”
The flows of electrons in two different directions with separate velocities causes a motion known as “space charge wheel”. This helps increase the electrons’ concentration, which further delivers enough power for the radio frequency oscillations.
Phase 4: Transformation of energy
Now, after the generation of the electron beam and its acceleration, the field acquires energies. The electrons also dispense some energy to the field. While travelling from cathode electrons dispenses energy at every cavity it passes through. Loss in energy causes a decrease in speed and eventually deceleration. Now, this happens multiple times. The released energy is efficiently used, and up to 80% efficiency is reached.
Health Related Concerns from Magnetron Microwave
A magnetron microwave produces microwave signals which may cause issue to human bodies. Some magnetrons consist of thorium in their filament, which is a radioactive element and not good for humans. Elements like beryllium oxides and insulators made with ceramics are also dangerous if they are crushed and inhaled. This can affect the lungs.
There are also chances of damages from overheating of magnetron microwave ovens. Magnetrons require high voltage power supplies. So, there is a chance of electrical hazards as well.
Before we start learning about the time domain reflectometer – TDR, let us know a reflectometer.
Reflectometer: A reflectometer is a type of circuit that isolates and samples the incident and reflected powers from a load using a directional coupler.
Reflectometers are prime applications of passive microwave components. A reflectometer is used in a vector network analyzer as it can measure various parameters like – reflection coefficient for the one-port network, scattering parameters for the two-port network. It can also be used in replacement of an SWR Meter or also as a power monitor.
Time Domain Reflectometer:A time-domain reflector or TDR is an electronic device based on a reflectometer’s property that finds out characteristics of electrical lines from the reflected waves.
TDRs are used for finding out faults in cables like twisted pairs of cables or coaxial cables. This article will learn more about the device, the uses of the time-domain reflector, and explanations about it.
A typical Time Domain Reflectometer, Image Credit: By Megger Ltd. – Megger Ltd, CC BY 3.0, Link
A TDR analyzes the reflected signals sent by itself. To analyze the reflections, it first transmits a signal along the cable and waits for the reflection. If there are some defects or mismatches in the transmission line or the cable, the part of the incident wave is reflected. TDR receives the reflected wave and then analyzes it to locate and measure the faults. But if there are no defects or everything is fine, then the signal reaches the far end without reflection, and the cable is considered acceptable. The working principle of a Time Domain Reflectometer is almost similar to the working principle of a RADR.
Analysis
The TDR analyzes the reflected wave. It is interpreted that the amplitude of the reflected wave determines the impedance of discontinuity. The reflected pulses also determine the distance of the reflected wave, which further determines the fault’s location.
Time Domain Reflectometer starts its operation by sending impulse or step signals or energies. Then it observes the reflected energy or the signals subsequently. The discontinuity of impedance is measured and analyzed by the reflected pulses of energies as the amplitude, magnitude, and waveforms help in analyzing.
For example, suppose an impulse function is sent from TDR towards a connected load. In that case, the reflectometer shows an impulse signal on its display, and the amplitude indicates the impedance of discontinuity. The following expression gives the relation between the load impedance and the magnitude of the reflected wave.
P = (RL – Z0) / (RL + Z0)
Z0 is the characteristic impedance of the transmission line or the coaxial cable. RL is the connected load resistance.
Any impedance discontinuity is observed as the termination impedance, and the termination impedance replaces it. The process consists of rapid changes in the characteristic impedance of the transmission lines.
Transmitted signals of TDRs
Time-domain reflectometers use various kinds of signals as incident signals. Some of the transmitters use pulse signals. Some of them use fast rise time step signals. Some of them also use impulse functions of signals.
TDRs using pulse signals send the pulse through the cable. Their firmness depends on the width of the pulse sent by them. That is why narrow pulse signals are preferred. But there is a shortcoming for the narrow width pulses as they are of high frequencies. High-frequency signals get distorted inside large cables.
Reflected Signals of TDR
Typically, the waves reflected from the load impedance or due to the impedance of discontinuity are similar to the incident waves in their shapes. Still, the magnitude and other properties get varied. If there is some change in the load impedance, the reflected wave does the exact change in its parameters to indicate the changes. For example, if the load impedance gets a step increased, the reflected wave will also have an increased step in it.
This property of reflected wave finds applications in many fields for Time Domain Reflectometer. TDRs are used to ensure the cable’s characteristic impedances, other impedance parameters, no mismatch at connectors or joints.
Time Domain Reflectors are mainly used for testing purposes of the very long cables. If any fault arises in very long cables, it is practically impossible to locate the fault after digging up the kilometers-long cable. That is when a TD reflectometer comes into action. The time-domain reflectometer is capable of measuring the resistances on connectors and can sense (detects) the faults way before the catastrophic failures.
TDRs also find applications in communication lines as they can catch any minute change of line impedance due to the introduction of any tap or splice.
Time-domain reflectometer devices are crucial for PCBs. Printed circuit boards designed for high frequencies need TDRs for their fault analysis. Some of the major applications are listed below in detail.
> Analysis of Semiconductor Devices
TDRs are useful for locating defects in a semiconductor package. Using the property of domain reflectometry, a TDR provides marks for each conductive trace. It is beneficial for finding out the exact location of the opening and shorts.
> Level Measurement using TDR
As mentioned earlier, TDRs are beneficial and essential devices for finding out and locating faults for long wire cables. A more advanced device – a TDR-based level measurement device can find out the level of a fluid using that ancient and fundamental property.
For measurement purposes, the device sends a signal through the cable or the waveguide. A part of the signal gets reflected after the signal incident or hits the medium’s target surface. Now, the device calculates the period by calculating the difference between the send time and the reflected wave’s receive time. The period now helps to determine the level of the fluid. As the device measures the fluid level, that is why it is called the Level Measurement Device.
The internal sensors of the device process the analyzed output using analog signals. But there are also some difficulties while the propagation of the signal gets varied by the medium’s permittivity. The moisture content also varies the propagation greatly.
> Applications of TDRs in Geotechnical Engineering
TDRs are extensively involved in the Geotechnical Engineering domain. They are used to observe the slopes’ movements using various tools like highway cuts, rail beds, and open-pit mines.
TDRs are also used for stability observation. In the process of observation, a cable is set up close to the concerning region. Any mismatch of insulators between conductors affects the electrical impedance of the coaxial cable. A hardcover surrounds the coaxial cable. It helps to interpret the earth’s movement via a rapid cable distortion. The deformation causes a peak in the monitor of the reflectometer device. Nowadays, signal processing techniques are doing the same job more efficiently.
> Determination of Soil’s Moisture
Time-domain reflectometers are used for determining the moisture level of soils. The process of measurement is quite a simple one. A TDR is placed inside different soil layers, and then the start time of precipitation and the time when the soil moisture increased is noted. TDRs are useful to measure the speed of water infiltration.
> Applications in Agricultural Engineering
As mentioned earlier, TDRs can measure the soil content. It is beneficial and crucial for the study of agriculture engineering and science. Researches and advanced studies have made time domain reflectometers more technically advance to measure the moisture content for soil and grain, foodstuff, and sediments. However, the primary building block remained the same. TDRs are very much renowned because of their accuracy in measurements.
> Applications in Aviation maintenance
The property of reflectometers has found applications in aviation wiring maintenance. The more specific property is the “Spread Spectrum Time Domain Reflectometry,” which is used to locate the fault and preventive maintenance. There are two main reasons behind using the property. The first one is the precision in the measurement, as the device gives accurate measurements. The second one is the TDR’s ability to locate defects in an extensive range that’s too in live.
Time Domain Reflectometers get modified and advanced with time. The optical time-domain Reflectometer is one of the advanced types of TDR. It is an equivalent device for optical fiber. There is also a device like Time Domain Transmissometry, which analyses transmissions of optical fibers. Two more variations are: “Spread Spectrum Time Domain Reflectometry (SSTDR)” and “Coherent Time Domain Reflectometry (COTDR)”.
Microwave tubes are generally divided into categories on the type of electron beam-field interaction. The types are –
Linear beam or “O” type
Crossed-field or “M” type
Linear-beam: In this type of tube, the electron beam traverses through the tube’s length, and it is parallel to the electric field.
Crossed-field: In this type of tube, the focusing field is perpendicular to the accelerating electric field.
Microwave tubes can also be classified into amplifiers or oscillators.
Klystron: Klystron is a type of microwave tubes which can amplify the higher range of frequencies, especially from Radio Frequencies to Ultra High frequencies. Klystrons can also be used as Oscillator.
In an amplifier, the electron beam is sent through two or more resonant cavities. The very first cavity receives the RF input and bunches it into high- and low-density regions to modulate the signal. The bunched beam then goes to the next cavity, which accentuates the bunching effect. In the following or final cavity, the RF’s power is extracted at a highly amplified level.
The two cavities generate about 20 dB of gain, and using four cavities may produce up to 80-90 dB of gain. Klystron amplifiers can peak powers in the range of megawatt. It has power conversion efficiencies of about 30% to 50%.
Operation of Klystron Amplifier
Klystron amplifiers amplify the Rf signal. It converts the kinetic energy of the signal in a DC electron beam into the RF power. Inside a vacuum, an electron gun emits a beam of electrons, and the high-voltage electrodes accelerate the electron beam.
Then, an input cavity resonator accepts the beam. Here some series of operation occurs. At first, the input cavity is fed with RF energy. It creates standing waves. The standing wave further produces oscillating voltages which function on the beam of an electron. The electric field bunched the electrons.
Every bunch enters into the output cavity when the electric field decelerates the beam by opposing the electron’s motion. That is how the conversion of kinetic energy to the potential energy of the electrons occurs.
Reflex klystron and Working of Reflex klystron
Reflex Klystron: Reflex klystron is a klystron with a single-cavity which acts as an oscillator by using a reflector electrode next to the cavity to deliver positive feedback through the electron beam. Reflex klystrons can be tuned mechanically to adjust the cavity size.
A reflex klystron is often called “Sutton Tube” after the name of scientist Robert Sutton, one of the Reflex klystron inventors. It is a low power klystron with applications as a local oscillator in some of the radar receivers.
In a reflex klystron, the electron beam is passed through the only cavity present in the klystron. After the pass, they get reflected by a reflector of a negatively charged electrode. They make another pass through the cavity. Then they are collected. When the electron beam has their first pass, they are velocity modulated. The electron bunches are formed inside the drift space of the reflector electrode and the cavity.
The reflector voltage is tuned to ensure the maximum branching. The electron beam gets reflected by the reflector and re-enters into the cavity. The maximum branching makes sure that the maximum amount of energy is transferred from the beam of an electron to the radio frequency oscillation. The electronic range of tuning of a reflex klystron is typically referred to as the change in frequency between two half PowerPoint.
Applications of Reflex Klystron
Some of the reflex klystrons are listed below.
One of the significant applications of reflex klystrons is in Radio and RADAR systems as the receivers.
They are also used as signal generators.
Reflex klystrons can be used as Frequency modulators.
Also, they can be used as pump oscillator and local oscillators.
Nowadays, most of the applications of reflex klystron has been replaced by semiconductor technologies.
Gyroklystron
Gyroklystron is one of the types of microwave amplifier whose working is almost the same as of a klystron. But for a Gyroklystron, unlike a klystron, the bunching of an electron is not axial. Instead, the modulation forces change the cyclotron frequency, and thus the azimuthal part of the motion creates the phase branching.
At the last or the output cavity, the received electrons transfer their energies to the cavity electric field, and the amplified RF signal can be coupled off from the cavity. The cavity structure of a Gyroklystron is cylindrical or coaxial. The main advantage of a Gyroklystron over a normal klystron is that a Gyroklystron is capable of delivering high power at high frequencies which is very difficult for a typical klystron.
Optical Klystron
Optical klystrons are the devices where the method of amplification inside is the same as of a klystron. The experiments are done primarily on lasers at optical frequencies, and they are known as Free Electron Laser. These types of devices use ‘undulators’ in the place of microwave cavities.
Two Cavity Klystron
Two cavity klystron is the simplest type of klystron available. As the name suggests, this type of klystron has two microwave cavities. They are known as ‘catcher’ and ‘buncher’. If the two cavities klystron is used as an amplifier, the buncher receives the weak microwave signal and couples out from the catcher, and it gets amplified.
Working of a Two Cavity Klystron
In this klystron, there is an electron gun which generates electrons. An anode is placed at a certain distance from them. Electron gets attracted by the anode and passes through them with high positive potential. An external magnetic field, outside the tubes, produces a longitudinal magnetic field along the beam axis. It helps to stop the beam from the spreading.
The electron beam first goes through the ‘buncher’ cavity. There are grids on both sides of the cavity. The electron beam produces excitation to the standing wave oscillations, which further causes an oscillating AC potential across the grids. The field’s direction varies two times for a single cycle. Electrons enter the cavity when the entrance grid is negative and exits when the exit grid is positive. The field affects the motion as it accelerates them. After the change of direction of the field, the motion of the electrons gets decelerated.
After the ‘buncher’ cavity there, coms the drift space’. The bunching of electrons occurs here as the accelerated electrons get bunched with the decelerated electrons. The length is made precisely so that the maximum branching occurs.
Then comes the ‘catcher’ cavity. It has similar grids on each side. The grids
absorbs the energy from the electron beams. Like the ‘buncher’ here, the electron moves due to the electric field’s change of direction and thus the electrons work. Here the kinetic energy produced by their movement is converted into potential energies. The amplitude of the oscillating electric field is increased to do so. That is how the signal of the ‘buncher’ cavity is get amplified in the ‘catcher’ cavity. Specified types of waveguides and transmission lines are used to couple out from the catcher cavity.
Klystron vs Magnetron (Difference between the Klystron and Magnetron)
To find out the differences between the Klystron and Magnetron, we have to know about the Magnetron.
Magnetron: Magnetron is a type of vacuum tube which generates signals of the microwave frequency range, with the help of interactions of a magnetic field and electron beams.
Points of Discussion
Klystron
Magnetron
Definition
Klystron is a type of microwave tubes which can amplify the higher range of frequencies, especially from Radio Frequencies to Ultra High frequencies.
The magnetron is a type of vacuum tube which generates signals of the microwave frequency range, with the help of interactions of a magnetic field and electron beams.
Frequency of operation
The operating frequency range for Klystron is 1 GHz to 25 GHz.
Working frequency range is 500 MHz to 12 GHz.
Efficiency
The efficiency is around 10% to 20%.
The efficiency of the magnetron is relatively high, and it is around 40% to 70%.
Output Power
Output power ranges between 1 milli-watt to 2.5 watts.
Output power ranges between 2 mW to 250kW.
Injection of Electrons
Electrons usually are injected from outside.
Electrons are injected forcefully from the outside.
Traversing path of the Electrons
Electrons traverse linearly along the axis.
Electrons traverse spirally along the axis.
Usability
Can be used as an amplifier as well as an oscillator.
Can be used as Oscillator only.
Applications
Klystrons are used in RADARS, like particle accelerators, transmitters, etc.
Magnetrons are used in many types of home appliances, including microwave ovens, special heaters.
To know about Standing Wave Ratio Meters, we should know what is SWR at first. SWR is an Acronym of “Standing Wave Ratio”, and it is defined as follow.
SWR or Standing Wave Ratio: Standing Wave ratio is defined as the ratio of the maximum RF voltage to the minimum RF voltage of a transmission line.
When the ratio is calculated with respect to the AC voltage, then the parameter will be called voltage SWR, and if the ratio is calculated with respect to current, then the SWR will be known as current SWR.
Standing waves are physically stationary waves but not like typical ones as the amplitude doesn’t change with respect to time. SWR is necessary for the measurement of impedance matching for loads of transmission lines in Microwave Engineering.
What is an SWR Meter?
SWR Meter: SWR Meter or Standing Wave Ratio meter or Wave Ratio Meter or VSWR Meter (Voltage Wave Standing Ratio Meter) measures the value of Standing Wave ratio of a transmission line.
The Standing Wave Ratio Meter actually measures the amount of mismatch present between the load and the transmission line associated with it. It also determines the amount of RF energy reflected by the transmitter.
The most common type of standing wave ratio meter contains a dual directional coupler which other samples out some amount of power in a direction. After that, a diode does some rectifications and applies to the meter.
This method of operation finds out a comparison between the minimum and maximum level of voltages. The standing wave ratio meters is applicable and useful for signal ranging from very high frequencies and above. It cannot be used for low-frequency signals.
VSWR meters measures voltage Standing Wave Ratio and ISWR meters measure current standing wave ratio.
Methods of Measurement of SWR
There many different methods available for measurement of SWR. The simplest method is the method of using a slotted line. The slotted line is a part or component of transmission lines with an uncluttered slot through which a probe gets passed. The probe does the main thing by allowing to measure voltages at various points.
Real World Applications of SWR Meter
Standing Wave Ratio Meter is one of the most critical and crucial devices for Microwave Engineering. SWR meters are widely used for setting up Antennas and connecting the antennas with their transmission lines. SWR Meters are also used for medical applications which are based on microwave engineering.
Let us discuss how an SWR Meter works or how a directional SWR works. A directional SWR meter is necessary to measure the amplitude of the transmitted wave as well as the amplitude of the reflected wave.
As the image shows, there is a transmitter (Tx) and an antenna (ANT) terminal connected with the help of a transmission line. Here, the significant line electromagnetically couples with the directional couplers. Resistors terminate the lines at one of the ends and diodes are connected at another end for rectification purposes.
The resistors help to match the characteristic impedance of the transmission lines, and the diodes allow the conversion of the amplitudes of waves to their equivalent DC voltage. At last, capacitors smoothen the final DC voltage. There are also connected amplifiers with the forward and reverse terminals. They function as the needed drain resistor and help to determine the Dwell Time.
VSWR meters or typical Standing Wave Ratio meters are easy to use and measure the standing wave ratio. The process of using an Standing Wave Ratio meter while doing an experiment or applying for other purposes are listed below. The steps will help to interpret the result from the meters.
An important point to be noted before using VSWR is that: VSWR should be used at low power and in the clear channel, primarily if the experiment aims to measure an antenna’s performance.
Step 1: Find a clear frequency channel – The frequency channel should be clear enough or noiseless enough so that the transmitted signal from both ends could be interpreted from both sides.
Step 2: Reduction of Power – The transmitted power should not exceed a specific power range so that the signal causes distortion at the output devices.
Step 3:Set up the Mode – The mode of operation should be set using the options available on the meter. Like – Amplitude Modulation, Frequency Modulation etc.
Step 4: Set up of Meter – Now we need to set the Standing Wave Ratio meter to the forward mode. To do so, check the front panel. Also, switch the adjustment knob downwards. It will help to restrict overloading.
Step 5: Adjustment of the Forward Reading – After the transmitter starts its transmitting job, keep adjusting the CAL knob to ensure a full-scale reading of the experiment.
Step 6: Set up of Meter – Now the Standing Wave Ratio Meter is set up again. This time the knob on the front panel is changed to ‘Reverse’ direction. This is done after the meter is set for forwarding power.
Step 7: Restrict the transmission – The transmission is stopped as soon as possible to restrict the VSWR meter’s overloading.
Step 8:Repeat the above steps for various frequencies – Took the readings for several other frequencies by following the same steps.
SWR Bridge
Impedance bridge is also capable of measuring Standing wave ratio. Impedance bridge is an LCR meter. When the given impedance gets matched with the reference impedance, the bridge gets balanced. If a transmission line gets mismatched, there is some deviation of input impedance, and that could lose the bridge’s balance. That is how a bridge can measure if there is some amount of SWR present in the connection.
Let us discuss the reading collected by Standing Wave Ratio Meters. Different values of Standing Wave Ratio meters describe different conditions.
Range of value
Explanation
SWR 1 to 1.5
It is considered as the ideal range of value. The reading can be decreased to 1 from 1.5 by doing some additional tuning.
SWR 1.5 to 1.9
It is not the best range, but fair enough. Such readings come from vehicle variables or installations faults. It is an acceptable range.
SWR 2.0 to 2.4
It is not a good range of value. There are scopes for improvement. This range of values come from poor antenna mounting location. Fixing that problem might improve your meter’s SWR value.
SWR 2.5 to 2.9
This range of value affects performance and lead to wrong impressions. The transmitter may also get a damaged—poor quality of equipment and needy mounting causes this range of values.
SWR > 3
Operation with this range of values is risky. The device will be damaged within a few moments. The transmission should be stopped at this range. The reason behind such worse values is major installation problems. Attach a proper ground with the device. This range can also indicate poor quality of antenna and faulty coaxial cables.
Point to be noted: Do not transmit a signal if the SWR range exceeds the range of 1.5 to 2. It will damage the transmitter. If you observe the reading is more than 2.5, shut down the transmitter as soon as possible.
Essential Formulas For calculation of SWR using SWR Meter
The formula for calculating VSWR is Vmax / Vmin.
Also, the expression for VSWR using the forward and reverse wave voltages can be written as: VSWR = (VFWD + VREV) / (VFWD – VREV)
There is another formula for calculation of SWR.
SWR = | 1 + Г| / | 1 – Г|
Digital SWR Meter
Nowadays, most of the analogue SWR meters are replaced by Digital SWR Meters. Digital SWR Meters are easier to use, take less time to get the result, smaller in size, and lower the maintenance cost than an analogue meter.
Limitations of Standing Wave Ratio (SWR) Meters
SWR Meters does not measure the physical impedance present for a load. Instead, it measures a ratio which gives us the idea of mismatch. The perfect impedance for the load can be measured using a separate device known as – “Antenna Analyzer”. The measurement is only possible if the SWR meter is set perfectly with the transmission line itself. It is matched with the characteristic impedance of the transmission line (generally 50 to 70 ohms).
SWR meters must be set up as close as possible concerning the transmission line. Otherwise, SWR creates some false impression regarding the readings.
Rectangular Waveguides are one of the primarily used transmission lines. The primary application of rectangular waveguides was the transmission of microwave signals. It has still some critical applications. Some of the components like – couplers, detectors, isolators, attenuators, and slotted lines are available in the market with their large variety for different waveguides band ranging from 1 to 22o GHz. Nowadays, modern devices are using planar transmission lines like stripline or microstrips rather than waveguides. It also helps the miniaturization of the devices. However, the waveguides still have significant applications, including high-power systems, millimetre wave applications, satellite systems, etc.
Rectangular waveguides of a hollow structure can propagate TE (transverse electrical) modes and TM (transverse magnetic) modes but not the TEM (transverse electromagnetic) modes. The reason behind such characteristics is the single conductor. This article will discuss the transmission of TE and TM modes and find out several properties of them.
As we know, TE modes of waveguides are specified by Ez = 0 and hz will satisfy the reduced wave equation. The reduced wave equation is given below.
Here, the cut off number is the kc. It is given as: kc = √ (k2 − β2) and Hz (x, y, z) = hz (x,y) e – jβz.
Now, the above equation can be solved using the method of separation of variables. Let, hz (x,y) = X (x) Y(y)
Substituting the hz in the equation, we get:
Following the usual separation of variables, as each of the terms must be equal to a constant, we provide separation constant kx and ky. Now, the equations are:
The constants also satisfy another condition. That is: kx2 + ky2 = kc2
The typical solution for hz comes as:
hz (x, y) = (A coskxx +B sinkxx) (C coskyy + D sinkyy).
To determine the constant value, boundary conditions have to apply on the electric field components in tangential direction to the waveguide’s wall. They are given below.
ex (x, y) = 0 for y= 0 and b.
ey (x, y) = 0 for x= 0 and a.
The values of ex and ey from hz comes as below. They are calculated from some other wave equations.
From the boundary conditions of ex and evaluated value of ex, D’s value comes as 0 and ky = nπ/b for n = 0, 1, 2…
Also, from the boundary conditions of ey and evaluated value of ey, B’s value comes as 0 and kx = mπ/a for m = 0, 1, 2…
At last, the solution of Hz comes as:
Hz (x, y, z) = Amn cos (mπx/a) cos (nπy/b) e – jβz
Here, Amn is an arbitrary amplitude constant which is made up of the constants A and C.
Now, the transverse field components of TEmn modes are specified below.
The propagation constant is given by:
β = (k2 – kc2)1/2 = (k2 – (mπ/a)2 – (nπ/b)2)1/2
Now, in reality, k > kc,
β = [(mπ/a)2 + (nπ/b)2]1/2
Now each mode (for each combination of m and n) has a cutoff frequency. It is specified by fcmn.
The mode having the lowest cutoff frequency is known as dominant mode. In the dominant mode, we assume that a > b. the minimum cut off frequency happens for the TE10 mode and cutoff freq. expressed as:
fc10 = 1 / (2aõe)
TE10 is the overall dominant mode for TE mode. Now for m = n = 0, all the expression comes to 0. That is why there is no TE00 mode.
The wave impedance with the relation of the transverse magnetic field and transverse electric field comes as ZTE = Ex / Hy = Ey / Hx = kη / β
Here, η = √µ/e. It is the intrinsic impedance of the material present inside the waveguide.
There is another important parameter present known as guide wavelength. It is defined as the difference between two equal-phase along the waveguide. The difference here means the distance. Guide Wavelength can be calculated as
λg = 2π / β > 2π / k = λ
Wherever, λ is the wavelength of a plane wave which is present in between the guide.
The following expression gives the phase velocity.
We know that TM modes are characterized by Hz = 0. And the Ez component must satisfy the reduced wave equation.
Here, Ez (x, y, z) = ez (x, y) e -jβz. Here, the cut off number is the kc. It is given as kc = √ (k2 − β2).
The solution is achieved using the same process as that of TE mode. The typical solution of ez comes as:
ez (x, y) = (A coskxx +B sinkxx) (C coskyy + D sinkyy)
Now, applying the bounding conditions, which are listed below, we get –
ez (x, y) = 0 for x= o and x = a,
and, ez (x, y) = 0 for y = 0 and y = b.
Now, from the boundary conditions of ez and evaluated value of ez, the value of A comes as 0 and kx = mπ/a for m = 0, 1, 2…
Also. from the boundary conditions of ez and evaluated value of ez, the value of C comes as 0 and ky = nπ/b for n = 0, 1, 2…
At last, the solution of Ez comes as:
Ez (x, y, z) = Bmn sin (mπx/a) cos (nπy/b) e – jβz
Here, Bmn is an arbitrary amplitude constant which is made up of the constants B and D.
The calculated transverse components for the TMmn modes are listed below.
The propagation constant is given by:
β = (k2 – kc2)1/2 = (k2 – (mπ/a)2 – (nπ/b)2)1/2
For TM modes, the dominant mode is TM11 as the other lower mode like TM00, TM01 or TM10 is not possible as the filed expressions become zero. The cutoff frequency for the dominant mode is given as: fcmn.
fc11 = (1/(2π√µe) * [(mπ/a)2 + (nπ/b)2]1/2
The wave impedance with the relation of transverse magnetic field and transverse electric field, comes as: ZTM = Ex / Hy = – Ey / Hx = ηβ / k
Solved Example on Rectangular Waveguide
1. A rectangular waveguide is filled up with Teflon, and it is copper K-band. The value of a = 1.07 cm and b = 0.43 cm. The operating frequency is 15 GHz. Answer the following queries.
A. Calculate the cut-off frequencies for the first five propagating nodes.
B. compute the attenuation because of dielectric and conductor loss.
Solution:
The permeability of Teflon is 2.08. tan delta = 0.0004
We know that the cutoff frequencies are:
fcmn = (c/(2π√µe) * [(mπ/a)2 + (nπ/b)2]1/2
Now, the values for different m and n values are calculated using the formula.
The below list shows the values.
The first five modes those will propagate through the rectangular waveguide are TE10, TE20, TE01, TE11 and TM 11.
