What is Non-Inverting Op-Amp : Working & Its Applications

An op-amp or operational amplifier is basically a high gain multi-stage differential amplifier including two inputs and one output. The typical op-amp is available in two configurations like inverting op-amp and non-inverting op-amp. In an operational amplifier, the non-inverting terminal is marked with a (+) sign whereas the inverting terminal is marked with a (-) sign which is also known as positive & negative terminals. So, this article discusses an overview of a non-inverting op-amp and its working with applications.


What is Non-Inverting Op-Amp?

Non-inverting op-amp definition is, when the output of an operational amplifier is in phase with an input signal then it is known as a non-inverting op-amp. In this amplifier, the input signal is applied to the +ve terminal of an operational amplifier. A non-inverting amplifier generates an amplified output signal that is in phase with the applied input signal.

How does Non-Inverting Op-Amp Work?

A non-inverting amplifier works like a voltage follower circuit because this circuit uses a negative feedback connection. So it gives a part of the output signal as feedback to the inverting input terminal instead of giving a complete output signal. The complement of this op-amp is inverting op-amp which generates the output signal that is 180 degrees out of phase. This circuit is ideal for impedance buffering applications due to high input and low output impedance.

Non-Inverting Op-Amp Circuit Diagram

The non-inverting op-amp circuit diagram is shown below. In this circuit configuration, the output voltage signal is given to the inverting terminal (-) of the operational amplifier like feedback through a resistor where another resistor is given to the ground. Here, a voltage divider with two types of resistors will provide a small fraction of the output toward the inverting pin of the operational amplifier circuit.

Non Inverting Op Amp Circuit
Non-Inverting Op-Amp Circuit

These two resistors will provide necessary feedback to the operational amplifier. In perfect condition, the op-amp’s input pin will provide maximum input impedance whereas the output pin will provide low output impedance.

Non-Inverting Op-Amp Voltage Gain

The amplification of op-amp mainly depends on two feedback resistors like R1 & R2 which are connected in the voltage divider configuration. Here, the R1 resistor is called a feedback resistor (Rf). The output of the voltage divider which is given to the inverting pin of the operational amplifier is equivalent to the Vin because Vin & junction points of the voltage divider are located across a similar ground node. Because of this, the Vout depends on the feedback network.

Non-inverting op-amp works through two rules like the current rule & the voltage rule. The Current rule states that there is no flow of current toward the inputs of an op-amp whereas the voltage rule states that the op-amp voltage tries to ensure that the voltage disparity between the two op-amp inputs is zero.

From the above non-inverting op-amp circuit, once the voltage rule is applied to that circuit, the voltage at the inverting input will be the same as the non-inverting input. So the applied voltage will be Vin. So the voltage gain can be calculated as,

The flow of current through the R1 resistor can be given as “Vin/R1”.

Based on the current rule, both the inputs don’t draw current, thus the flow of current will be throughout R2.

After that, the output voltage (Vo) can then be Vout = Vin + (Vin/R1)*R2.

The non inverting op-amp gain formula is Av = Vout/Vin = 1+ (R2/R1).

Here, the gain value should not be < 1. Therefore the non-inverting op-amp will generate an amplified signal that is in phase through the input.

In the above equation Av = Op-amp’s voltage gain

‘R2’ is a feedback resistor

‘R1’ is a resistor connected to the ground.

Input Impedance

In a non-inverting operational amplifier circuit, the input impedance (Zin) can be calculated by using the following formula.

Zin = ( 1+ Aα β)*Zi

In the above equation, ‘Aα’ is an open-loop voltage gain

‘Zi’ is the input impedance of op-amp without using feedback

‘β’ is a feedback factor

So, the feedback factor for a non-inverting amplifier can be calculated as

β = R2/(R1+R2)

β = 1/ ACL

So, for a non-inverting operational amplifier circuit, the input impedance (Zin) can be calculated as

Zin = ((1 + (Aα / ACL))*Z1

Output Impedance

In the non-inverting operational amplifier, the output impedance can be measured as

Zout = Zo/(1+ Aα β)

We know the feedback factor β = 1/ACL, so the output impedance for a non-inverting op-amp can be calculated as

ZOUT = Zo /(1 + (Aα /ACL))

Non Inverting Op Amp Waveform

The input & output waveforms of non-inverting op-amp waveforms are shown below. The signal which needs to change is given to the +ve terminal of the op-amp whereas the –ve terminal is connected to GND with the help of an R1 resistor. The input (Vin) & output (Vout) voltages are within phase through each other, so their phase difference is 0 degrees or 360 degrees.

Output Waveforms
Output Waveforms

So the positive sign specifies that there is no phase shift between input & output. The voltage gain is dependent on two resistances R1 and Rf. By changing the values of the two resistances required gain can be adjusted.

Non-Inverting Op-Amp Solved Problems

For the following non-inverting amplifier circuit, calculate the following.

Non-Inverting Op-Amp Example Problem
Non-Inverting Op-Amp Example Problem
  • The flow of current throughout the load resistor
  • Amplifier gain
  • Output voltage
  • The o/p current

The values are Vin = 2V, R1 = 6 Ohms, Fr = 10 Ohms, RL = 3K Ohms.

1). The flow of current I1 = Vin/R1

= 2/6 = 0.33 mA

2). Non-inverting op-amp gain can be calculated as

Gain = 1 + (Rf/R1)

= 1+ (10/6) = 2.66

3). The o/p voltage (VO) = ACL * VIN = 2.66 * 2V = 5.32V

VO = 5.32V

4). The flow of current supply throughout the load resistor,

IL = VO / RL = 5.32/3 = 1.773 mA

5). The o/p current can be calculated by applying KCL (Kirchhoff’s Current Law) to the above circuit then,

IO = I1 + IL

IO = 0.33mA + 1.773 mA => 1.28 mA = 2.103

2). In the non-inverting amplifier, if the values of R1 = 50 kilo ohms, R2 = 1000 kilo ohms & Vin = 2v, then calculate the gain and output voltage.

Gain (AV) = 1 + (R2 / R1)

1+ (1000/50) = 1 + 20 => 21

If the input voltage (Vin) is 2v then the output voltage would be: 2 X 21 = 42v

Non-Inverting Op-Amp with Two Voltage Sources

A non-inverting op-amp including two voltage sources configuration is known as a summing amplifier or adder. So this is one of the most essential applications of an op-amp. In the summing amplifier circuit, multiple voltage sources are used.

The non-inverting summing amplifier circuit uses the configuration of a non-inverting op-amp circuit. In that, the input is given to the non-inverting terminal whereas the necessary negative feedback & gain can be attained by giving some portion of the o/p signal as feedback to the inverting terminal.

The main benefit of the non-inverting summing amplifier circuit is there is no effective earth condition across the input terminals; its input impedance is much higher than that of the standard inverting amplifier configuration. So the flow of current in the non-inverting op-amp with two voltage sources can be defined as:

Non Inverting Op Amp with Two Voltage Sources
Non-Inverting Op-Amp with Two Voltage Sources

According to KCL

IR1 + IR2 = 0

(V1-V+/R1) + (V2-V+/R2 = 0

The above equation can be written as

(V1/R1-V+/R1) + (V2/R2-V+/R2) = 0

If we make the above two resistances to equal then R1=R2=R

V+ = (V1/R + V2/R)(1/R+1/R) => (V1+V2/R)/2/R

Therefore, V+ = (V1 + V2/2)

The typical voltage gain equation for a non-inverting summing amplifier circuit can be given as

Av = Vout/Vin = Vout/V+ = 1+RA/RB

Vout = (1+RA/RB)*V+

Therefore, Vout = (1+RA/RB) V+V2/2

The closed-loop voltage gain of the non-inverting amplifier is AV is given as (1 + R /R). If we make this equal to 2 through making R = R, then the Vout becomes equal to the addition of all the input voltages.

Vout = (1+RA/RB) V+V2/2

If RA = RB then

Vout = (1+1) V+V2/2 => 2 (V1+V2)/2

So, Vout = V+V2

Similarly, for 3 input voltages non-inverting summing amplifier configuration, the closed-loop voltage gain is set to 3 to make the output voltage equivalent to the sum of the 3 input voltages, like V1, V2 & V3.

Advantages

The advantages of non-inverting op-amp include the following.

  • The output signal can be attained devoid of phase inversion.
  • The voltage gain is changeable.
  • The voltage gain is positive.
  • Better matching of impedance can be obtained with the non-inverting amplifiers.
  • The impedance value of i/p is high as compared to the inverting amplifier.
  • This op-amp circuit provides maximum input impedance including other op-amps benefits.
  • This configuration is used most frequently in different electronic devices.

Disadvantages

The disadvantages of non-inverting op-amp include the following.

  • As compared to inverting op-amps, non-inverting op-amps don’t provide more stability to the system.
  • The number of stages is used depending on the necessity of attaining the required gain.
  • Based on the particular amplifier, the input & the output resistance will be changed.
  • The amplifying circuit has no virtual ground, so it has a large common-mode voltage, and the anti-interference ability is relatively poor. So that the op-amp requires a higher common-mode rejection ratio, and another disadvantage is that the amplification factor can only be greater than one.

Where are Non-Inverting Op Amps used?

The applications of non-inverting op-amp include the following.

  • The non-inverting op-amp circuits are used where high input impedance is necessary.
  • These circuits are used as a voltage follower by giving the output to the inverting input as an inverter.
  • These are used to isolate the particular cascaded circuits.
  • The non-inverting op-amp is applicable where the amplified o/p is necessary within phase through the i/p.
  • It is used to perform mathematical stimulation like an adder.

What is the formula for a non-inverting amplifier?

The noninverting amplifier formula is Vout/Vin = 1+(R2/R1).

Is op-amp gain negative?

Op-amp gain mainly depends on its configuration. For inverting op-amp, the gain is negative like Av = Vout/Vin = -Rf/Rin whereas non-inverting op-amp, the gain is positive like AV = Vout/Vin = 1+Rf/Ri

Why is gain negative in op-amp?

The inverting op-amp gain is negative because the output of the op-amp is out of phase with the input.

Thus, this is all about an overview of a non-inverting op-amp which includes its configuration, voltage gain, input & output impedance, example problems with applications. This operational amplifier configuration uses a negative feedback connection with a voltage divider bias. The voltage gain of this op-amp is always >1 and it depends on the values of the resistor only. Here is a question for you, what is an inverting op-amp?

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