<P> The CMRR is defined as the ratio of the powers of the differential gain over the common - mode gain, measured in positive decibels (thus using the 20 log rule): </P> <Dl> <Dd> C M R R = (A d A c m) = 10 log 10 ⁡ (A d A c m) 2 dB = 20 log 10 ⁡ (A d A c m) dB (\ displaystyle \ mathrm (CMRR) = \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) = 10 \ log _ (10) \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) ^ (2) (\ text (dB)) = 20 \ log _ (10) \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) (\ text (dB))) </Dd> </Dl> <Dd> C M R R = (A d A c m) = 10 log 10 ⁡ (A d A c m) 2 dB = 20 log 10 ⁡ (A d A c m) dB (\ displaystyle \ mathrm (CMRR) = \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) = 10 \ log _ (10) \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) ^ (2) (\ text (dB)) = 20 \ log _ (10) \ left ((\ frac (A_ (\ mathrm (d))) (A_ (\ mathrm (cm)))) \ right) (\ text (dB))) </Dd> <P> As differential gain should exceed common - mode gain, this will be a positive number, and the higher the better . </P>

What do you mean by cmrr of an opamp