# Differential amplifier - what is the differences between CMRR and CMR?

I know that CMRR is Common-Mode Rejection Ratio, but what is CMR?

$$CMRR = \dfrac{A_{dm}}{A_{CM}}$$

I didn't find any mention of it in Sedra & Smith bible.

Does anyone know what CMR is?

CMR is "Common Mode Rejection"
It is the tendancy of the device to reject the input signal common to both the inputs
is called Common Mode Rejection.
its Measure is called "common mode Rejection Ratio". Which are denoted in decibels.

It's the same thing, just an abbreviation for Common Mode Rejection.

Apparently there is common terminology for CMRR and CMR, therefore I'll write here what I have found. This terminology is used by the Analog Device (AD 626) data sheet.

CMR is the Common Mode Range of the amplifier, that is, the range of DC values on which the differential small signal can be superimposed and still amplified (linearly) by the amplifier.

CMRR as been mentioned in the question is $20\;log_{10} \dfrac{A_{dm}}{A_{CM}}$.

CMR has gain units. Example: (V/V).

CMRR is the same, but with dB units.

You can use either one or the other with the nexo expression:

$$CMRR=20\;log_{10}CMR$$

CMR = 20 LOG(CMRR).

Here LOG means log base 10

• Could you please provide references or a basis for this answer? Not questioning the validity of the answer, but the provenance. – Anindo Ghosh Jul 20 '13 at 8:24