Common-Mode Rejection Ratio (CMRR)
The common-mode rejection ratio (CMRR) in a differential amplifier serves as a measure of the amplifier’s ability to reject unwanted common-mode signals, such as noise. It is defined as the ratio of the differential gain (Av(d)) to the common-mode gain (Acm).
A higher CMRR indicates better performance, as it implies a higher differential gain and lower common-mode gain. In practical terms, a CMRR of 10,000, for instance, means that the desired differential input signal is amplified 10,000 times more than unwanted common-mode noise. This ratio is crucial in eliminating noise or interference, contributing to the overall effectiveness of the differential amplifier.
This ratio is the Common-Mode Rejection Ratio, CMRR.
CMRR=Av(d)/Acm
The higher the CMRR, the better. A very high value of CMRR means that the differential gain Av(d) is high and the common-mode gain Acm is low.
The CMRR is often expressed in decibels (dB) as:
CMRR (dB)=20log10(Av(d)/Acm)
