Op-Amp: CMRR (Common Mode Rejection Ratio) Explained (with example)

In this video, what is Common Mode Rejection Ratio (CMRR) in op-amp and what is the importance of CMRR has been explained with the example.

What is CMRR?
CMRR is the ratio of differential gain and the common mode gain.
For ideal op-amp, the value of CMRR is infinite, but for practical op-amp's the value of CMRR used to be in the range of 80 to 100 dB.

Common mode gain is the gain of op-amp when same input is applied or same input is present at both input terminals.
Op-Amp in open loop condition acts as a differential amplifier and amplifies the difference between the two input terminals.
So, if both inputs are equal then the output of the op-amp in ideal condition should be zero.
But actually, some output used to be present at the output terminal.
And the ratio of this common output to the input voltage is known as the common mode gain.
For ideal op-amp, the value of common mode gain should be zero. But practical op-amp has some finite value (less than 1) of common mode gain.

Noise is the main source of common mode input signal. And op-amp should be able to suppress this noise as much as possible.
And how well it is able to suppress this noise is represented by this CMRR.

The timestamps for the different topics covered in the video.

0:20 What is CMRR and what is the importance of CMRR.

4:58 Example

This video will be helpful to all the students of science and engineering in understanding the concept of CMRR in op-amp.


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