Operational AmplifierBy : Sankalp - 02-Apr-2018 What is CMRR in Op-Amp? Like 1 likes - 2 comments 1 2 3 4 5 6 7 8 9 10
Anil03-Apr-2018
Let us first understand the meaning of common mode signal. Basically Op-Amp is designed to only amplify the differential voltage at the input side. Common mode signal are those which are having same magnitude and phase and common to input terminals of Op-Amp and these are induced due to electromagnetic interference, unwanted transient voltages and appeared at the input side along with differential voltages. Whenever such types of signals are present, Op-Amp rejects these signals as much as possible and tries to produce the output of differential voltages only based on its CMRR value.
So CMRR is basically the ability of Op-Amp to rejects the common mode signals at the input. The Op-amp with higher CMRR will reject more unwanted signals. As Op-amp output is sum of common mode signal and differential voltage signal of the input terminal of Op-Amp. That’s why Op-Amp is designed with high CMRR.
CMMR= Ad/Ac, Where Ad= Differential voltage gain, Ac= common mode voltage gain (=0 for ideal Op-AMP)
Therefore CMMR is infinite for ideal Op-Amp.