Configuration of Op-Amp

Configuration of op-amp means the ways in which an op-amp is connected in circuit. Based on the connection, the op-amp can work in two different modes.

1. Open loop mode

2. Closed loop mode

Open Loop Configuration of Op-amp

When no part of output is connected to input, it is known as open loop configuration. It means that there is absolutely no feedback present from output to Input.

Following figure shows an open loop configuration of op-amp.

open loop configuration of op amp,

Input signals V1and V2 are applied to non-inverting and inverting terminal respectively.

Differential Input voltage (Vid) is the difference between the voltages applied at non-inverting and inverting terminals.

Therefore it is,

Vid = (V1-V2)

Output voltage is given by,

 Vo=Av . Vid

Vo= Av(V1-V2)


Avisthe open loop gain gain of the op-amp.Ideally open loop gain is infinite but practically it’s value is very high.

As AVis very high, a small value of Vidwill drive the Op-amp into positive or negative saturation.

Vo= ± Vsat

When the output voltage of the circuit exceeds the possible range, the op-amp is said to saturate. It just provides its maximum or minimum possible voltage.

Depending on the polarity of Vid, the output voltage is equal to +Vsat or –Vsat.

Means, If Vid is positive then the output of op-amp is positive saturation. Also, if Vid is negative, the output of op-amp is negative saturation.

A very small value of differential input voltage will drive the op-amp into positive or negative saturation. Therefore the output voltage is not proportional to differential input voltage. Hence open loop configuration is not used for linear amplification.

Closed Loop Configuration of Op-amp

When a part of output is connected to (or fed back to) the input, it is called as closed loop configuration. It means that, some kind of feedback is present in the circuit.

Types of feedback

  • Positive feedback or regenerative feedback
  • Negative feedback or degenerative feedback

Positive Feedback

In positive feedback, the feedback signal and the original input signal are in phase with each.

Here, the feedback is present between non-inverting terminal (+) through resistor Rf.

It is used in oscillators and Schmitt triggers.

Negative Feedback

If the feedback signal and the original input signal are 180° out of phase, then it is called as negative feedback.

Here the feedback is present between output and inverting terminal (-) through resistorRf. Negative feedback is used in almost every circuit (except few) using op-amp.

For example, circuits like inverting op-amp, adder, subtractor and integrator use negative feedback.

Following fugure shows the negative feedback through a resistance Rf . It is a closed loop configuration of Op-amp.

closed loop configuration of op amp

Advantages of Negative Feedback

  1. Reduces the distortion.
  2. Reduces and stabilizes the gain.
  3. Increases the bandwidth.
  4. Changes values of input and output resistance.
  5. Reduces the effects of variations in temperature and supply voltage on the output of Op-amp.

Comparison of Open Loop and Closed Loop

Following table shows the comparison between open loop configuration and closed loop configuration of op-amp.

Sr. No.


Open Loop

Closed Loop


Type of feedback

No feedback

Positive or negative feedback


Voltage gain

Very high



Input resistance

Very high

Depends on the circuit


Output resistance


Very low




Very high



Waveform distortion

Low gain



Differential, Inverting, Non-inverting

Inverting, Non-inverting, Summing




Amplifier, Oscillator

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