An OP AMP has CMRR = 100 dB and open-loop gain = 250000.

Determine the common mode gain ACM

ACM = 2.5

Explanation:

The common mode rejection ratio, is a parameter that is used to measure the ability of an Operational-Amplifier, to reject or eliminate the noises of same polarity. The common mode rejection ratio is given by the following formula:

CMMR = AV/ACM

for the value of CMMR in deciBels (dB), the formula becomes:

CMMR = 20 log (AV/ACM)

where,

CMMR = Common Mode Rejection Ratio = 100 dB

AV = Open Loop Gain = 250000

ACM = Common Mode Gain = ?

Therefore,

100 = 20 log (250000/ACM)

100/20 = log (250000/ACM)

10⁵ = 250000/ACM

ACM = 250000/10⁵

ACM = 2.5