Understanding Common Mode Rejection Ratio (CMRR) in Differential Amplifiers

CMRR stands for Common Mode Rejection Ratio. It is a measure of how well a differential amplifier can reject any common-mode noise that may be present on both input terminals.

In other words, CMRR measures the ability of a differential amplifier to distinguish between two different signals that are present on its input terminals, when those signals are identical (i.e., have the same amplitude and phase) on both inputs. The higher the CMRR, the better the amplifier is at rejecting any common-mode noise and the more accurate it will be in amplifying only the difference between the two input signals.

CMRR is typically expressed as a decibel (dB) value, with higher values indicating better rejection of common-mode noise. A CMRR of 0 dB indicates that the amplifier cannot distinguish between the two input signals and is essentially acting as a single-ended amplifier. A CMRR of 60 dB or higher is generally considered to be a good level for most differential amplifier applications.