A Complete description of non-inverting amplifier | 5+ important facts

Non-Inverting Amplifier

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Points of Discussion

Introduction to Non-Inverting Amplifier

The non-inverting amplifier is another mode of operation for a standard amplifier. As we know, typical amplifiers have two terminals – inverting and non-inverting. When inputs are supplied through non-inverting terminals, that mode of operation is known as a non-inverting amplifier.

Non inverting amplifier theory

The working principle or the theory behind the non-inverting amplifier is the same as an inverting amplifier and for non-inverting amplifier, the input is provided in the non-inverting terminal. The amplifier amplifies the output with a particular gain and gives it in production. The gain is dependent on the resistance values, and the feedback system is connected with the inverting amplifier to generate negative feedback in the system. As the system has negative feedback, this amplifier has more stability but a lower gain than an inverting amplifier with the same resistance values.

Non inverting Amplifier Circuit Diagram

The below image depicts the circuit diagram of a non-inverting amplifier. In the below image, Vin is the input voltage for the amplifier, R1 is the primary resistance, Rf is the feedback resistance, and ‘I’ is the current through the feedback resistance. Study the image carefully as this image will be referred to as the non-inverting amplifier image throughout the article.

non-inverting amplifier
Image Credit: InductiveloadOp-Amp Non-Inverting Amplifier, marked as public domain, more details on Wikimedia Commons

Non inverting amplifier Design

Designing a non-inverting amplifier is quite a simple and straightforward task. Initially, the op-amp is set with its positive and -ve. reference voltage and ground contacts are made as required. Now, as it is a non-inverting amplifier, the input voltage is provided at the non-inverting and inverting terminal is connected to the ground through a resistance and standard feedback resistance is associated with the inverting amplifier to provide -ve. feedback in the Non-inverting Amplifier Circuit.

How does a noninverting amplifier work?

The non-inverting amplifier amplifies the input signal provided at the non-inverting amplifier and resistances in the amplifier’s design act as the gain factor in a particular mathematical equation. Due to the virtual grounding, the B point’s voltage also appears at the ‘A’ end. That is how the A node has the same voltage as the input voltage. Again, the same current will flow through the inverting terminal as that of the feedback path.

Non-inverting amplifier derivation

Let us derive the Non inverting amplifier equations and other essential formulas. At first, assume that virtual shorting works for the amplifier.

Then, the voltage at the B node will be equal to the voltage at the A node.

Now, VB = Vin.

The Vin thus will appear at the A node also. Therefore, we can say,

VA = Vin.

Let us assume the output voltage is Vo. The feedback resistance is said to be Rf. The current through the feedback path is ‘I’. The ‘I’ can be written as below.

I = (Vo – VA) / Rf

Or, I = (Vo / Rf) – (VA / Rf) —- (1)

The same current flows through the inverting terminal. So, the equation for that terminal,

I = (VA – 0) / R1 = VA / R1 = Vin / R1 —- (2)

Equating equation (1) and equation (2), we can write –

(Vo / Rf) – (Vin / Rf) = Vin / R1

Or, Vo / Rf = Vin / R1 + (Vin / Rf)

Or, Vo / Rf = Vin [ (1/R1) + (1/Rf)]

Or, Vo / Rf = Vin [ (Rf + R1) / (R1 Rf)]

Or, Vo = Vin [(Rf + R1) / R1]

Or, V0 = Vin [ 1 + (Rf/R1)]

This is the final output of the non-inverting amplifier.

Non inverting amplifier Equation

The final output equation of the circuit is known as the non inverting amplifier equation. The equation gives the relation between the input and output voltage. The gain factor can also be observed in the equation.

V0 = Vin [ 1 + (Rf/R1)]

This is the non inverting amplifier equation. The Rf is the feedback resistance, R1 is the resistance connected at inverting terminal. The Values of these resistances affects the input voltage. As we can see, if the value of (Rf/R1) is greater than 1, then we have gained in the system. So the (Rf/R1) factor needs to increase as much as possible. But that can be done to an extent.

Non inverting amplifier Vout

The vout or the output voltage of the non inverting amplifier tells us why this set of operation in the amplifier is called the non-inverting amplifier. The output equation of the non inverting amplifier is given as V0 = Vin [ 1 + (Rf/R1)].

From the above equation, we can observe that the output and input voltage are in the same phase of operation. Unlike an inverting terminal, the output of the amplifier is not inverted to the negative phase. That is why the operation set is called a non inverting amplifier.

Non inverting amplifier input impedance

An ideal op-amp has the property of high input impedance and that is why every amplifier are designed to have greater input impedances. Non-inverting amplifiers are no exceptions. They show higher input impedances in operations.

Gain of non inverting amplifier

The output of an amplifier is the input multiplied by the gain. The gain of amplifiers depends on the resistance values and the type of feedback the amplifier has. For the negative feedback system, the gain decreased, and the system’s stability increases, and for positive feedback, the gain is higher, but the strength of the system gets decreased.

For the equation: Vout = k * Vin, k is the gain of the amplifier.

(Point to be noted: Gain is a ratio of the output voltage to the supplied input voltage. That is why it has no units.)

Non-inverting amplifier gain

We have discussed earlier what is gain meant for a non-inverting amplifier. Let us find out the exact expression for the gain of a non inverting amplifier.

The general expression of the amplifier’s output voltage is Vout = k * Vin.

The O/P equn of the non-inverting amplifier formulated as  

V0 = [ 1 + (Rf/R1)] * Vin.

So, k can be computed as by the comparison of above two equations.

k = [ 1 + (Rf/R1)].

This expression of the resistor is known as the gain of the non-inverting amplifier and from this, we can observe that if Rf = R1, Vo = 2 * Vin. So, the input voltage gets amplified by a factor of 2. The (Rf/R1) ratio typically controls the gain. Increasing Rf increases the gain value.

Non inverting op amp negative gain

A detailed analysis of the gain of Non-inverting op amp is done previously. Non inverting op amp negative gain is referred to as the exact gain of the amplifier. It is given a different nomenclature because the op-amp is provided with negative feedback. Though the term is misleading, many readers think it indicates a non-inverting amplifier provides the negative magnitudes of gain.

Non inverting amplifier transfer function

The transfer function of a system refers to the process which describes or provides output for each input. As the amplifier takes two inputs and amplifies them, the transfer function will reflect the same. The transfer function can be written as:

Vo = k * Vi

Here Vo and Vi are the two inputs, and k is the gain.

Non inverting amplifier breadboard

To observe and examine the functionality of a non inverting amplifier in real, we need to make a circuit using a PCB or a breadboard. The experiment requires some equipment. They are listed below.

  1. Resistances of 1 kilo-ohm and ten kilo-ohms.
  2. IC741
  3. Connecting Wires
  4. CRO
  5. Breadboard
  6. DC voltage supply

The connection of the breadboard is given below. Connect the equipment properly and observe the output waveform in the CRO.

Bandwidth of non inverting amplifier

Before learning about the bandwidth of a non inverting amplifier, let us know the bandwidth of an amplifier. Bandwidth is mentioned to as the range of freq over which the amplifier of amplifier gets above 70.7%.

Bandwidth of a non inverting amplifier is determined by considering the gain-bandwidth product and then dividing it by the non inverting gain.

Non inverting amplifier phase shift

Typically, the phase shift is referred to as the change in the magnitude of the input signal. There is a black box, and we provide an input signal of +5 V. Now, if we receive -10 V as an output, then there is a phase shift inside the black box. The same happens for the amplifiers. As we provide input to the non inverting amplifier, there is no change in the phase of a voltage of an output voltage. So, we can say there is a 0o change in the output. For an inverting terminal, the phase shift is -180o.

Non inverting summing amplifier gain

The summing amplifier provides the amplified summation of the input voltages as the output. In the below circuit, we have given two input voltages as V1 and V2 in the amplifier’s non-inverting terminal as we want to create a non-inverting summing amplifier.

non-inverting amplifier
Image by: InductiveloadOp-Amp Summing Amplifier, marked as public domain, more details on Wikimedia Commons

Applying superposition theory to determine the voltage at nodes, we equate the current values from the feedback branch and the inverting terminal branch.

The output equation comes as: Vout = [1 + (Rf/Ra)] * [ (V1 + V2) / 2]

So, the non inverting summing amplifier gain is [1 + (Rf/Ra)] and this is similar to typical non inverting amplifiers.

Application of non inverting amplifier | Non inverting amplifier uses.

  • One of the significant applications of non-inverting amplifier is to offer high input impedance and this non-inverting op amp is very efficient for this.
  • Non inverting op-amps are used to differentiate between small circuits inside a cascaded and complex course.
  • They are also used in varying gain consideration.

What are non inverting amplifiers used for?

Non inverting amplifiers are used for their high impedance values and better stabilities due to negative feedback and gain. The property of non inverting amplifier that gives gain or resistance at the output made it famous for circuit differentiation for cascaded systems.

Inverting vs non inverting amplifier noise

Inverting amplifiers provide more noise gain than non inverting amplifiers. It happens because the source of current and voltages find different gain value to the output. The noise gain is a very crucial parameter to measure the performance of the amplifier.

Non inverting buffer amplifier

Non inverting buffer amplifier or the buffer amplifier, or the buffer op-amp, is a particular type of op-amp that takes the only input through the non-inverting amplifier and provides unit gain. The inverting terminal is short-circuited, with the output creating negative feedback. Such amplifiers offer high input impedance, lower output impedance and high current income.

Buffers are used for a circuit breaker or to avoid the loading of the input.

non-inverting amplifier
Image by: InductiveloadOp-Amp Unity-Gain Buffer, marked as public domain, more details on Wikimedia Commons

Non inverting amplifier with capacitor

A capacitor can be added with a non inverting amplifier to implement various transfer functions. A capacitor can make the non inverting amplifier into an integrator or a differentiator.

Using the capacitors, non inverting amplifiers can also be transformed into AC coupled circuits, or a ‘half supplied rail’.

Non inverting amplifier with reference voltage

Non inverting amplifiers are configured with reference voltages. Reference voltages are essential for op-amps as they are the bounding limit for the outputs. An amplifier cannot go beyond the positive reference voltage or go below the negative reference voltage.

Frequently Asked Questions

1. What is a non inverting amplifier used for?

Answer: Non inverting amplifiers are used for their high impedance values and better stabilities due to negative feedback and gain. The property of non inverting amplifier that gives gain or resistance at the output made it famous for circuit differentiation for cascaded systems.

2. Which is a better inverting or noninverting amplifier?

Answer: Inverting amplifiers are more preferred than noninverting amplifiers. The slew rate and standard mode rejection ratio (CMRR) is higher for an inverting amplifier than a non inverting amplifier.

3. Draw non inverting amplifier waveform.

Answer: The below image depicts the non-inverting amplifier waveform. We can observe that the output is amplified and is in the same phase as the input.

non-inverting amplifier
Waveform

4. For what application is an inverting amplifier used, and for what application is a non inverting amplifier used?

Answer: Applications where the user needs higher gain, better slew rate, better CMRR will choose the inverting amplifier. And if a user needs higher dynamic stability of the system, he should apt for the non inverting amplifier.

5. What are the advantages of an inverting amplifier as opposed to non inverting?

Answer: An inverting amplifier provides more gain, a better slew rate, higher CMRR than a non inverting amplifier.

6. What are the typical conditions of non inverting amplifier to operate in the linear region?

Answer: Let us consider, Rs is a typical input resistance, Rf is the feedback resistance, Vcc is the saturation voltage, and Vg is a reference voltage. The condition for working in the linear region of an ideal op-amp will be:

(Rs + Rf) / Rs > |Vcc / vg|

7. Why is a virtual ground not applied to a non inverting amplifier?

Answer: Though learners frequently ask the question, there is a technical fault in the problem itself. Virtual Ground is a property of the amplifier, but it is not a statute which can be applied actually. Now, for a non inverting terminal, there is no node present in the circuit, which is not good.

8. Why is the I P resistance of inverting and non inverting opam infinite?

Answer: The input resistance of non inverting op amp is infinite, but practically if this value of impedance gets increased, then the lesser the current it will actually draw. The condition is necessary for the op-amp to perform and amplify the week signal efficient way.

9. Why is there no voltage over the feedback resistor in a non inverting amplifier?

Answer: For a voltage follower non-inverting circuit, there is no voltage drop across the inverting terminal and for the ideal case, there should not be any current through the resistor.

10. Why must feedback resistors value be greater than input resistors value in the case of an OP amp non inverting amplifier?

Answer: The gain of a non inverting amplifier is given as [1 + (Rf/Ra)]. We can observe that increasing the Rf (feedback resistance) will increase the system’s overall gain. That is why the feedback resistor value is kept more excellent than the input resistance values.

11. What will happen if I want to add a positive feedback capacitor in a non inverting amplifier? What about the noise and phase margin?

Answer: If you add a positive feedback capacitor to a non inverting amplifier, the circuit will work as a Multi-vibrator. The RC value will control the oscillation.  The noise and phase margin is not that much of importance.

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