A certain diff. amplifier has a differential voltage gain of 2000 and a common mode gain of 0.2. The CMMR in decibels (dB) is: 

CMRR (Common mode rejection ratio) is defined as the ratio of differential-mode voltage gain (Ad) and the common-mode voltage gain (Ac).

Mathematically, this is expressed as:

Ad = Differential gain

Ac = Common mode gain

Calculation:

Given:

Differential voltage gain (Ad) = 2000

Common-mode gain (Ac) = 0.2

Common mode rejection ratio (CMRR) is given by,

\(CMRR = 20\log \left| {\frac{{{A_d}}}{{{A_c}}}} \right| \)

\(CMRR= 20\log \left| {\frac{{2000}}{{0.2}}} \right| = 80\;dB\)