When a given op-amp has 10 V common-mode inputs, the output of the device is 10 mV. When this same device has a 2 mV differential input, the output of the device is 10 V. What is the CMRR of the device?
A) 5:1
B) 5000:1
C) 1000:1
D) 5,000,000:1

Question

Quizplus · Accepted Answer

CMRR (Common Mode Rejection Ratio) is calculated as the ratio of differential gain (Ad) to common-mode gain (Acm). Given that the output for a 2 mV differential input is 10 V, the differential gain (Ad) is 10 V / 2 mV = 5000. For a 10 V common-mode input, the output is 10 mV, so the common-mode gain (Acm) is 10 mV / 10 V = 0.001. Thus, CMRR = Ad / Acm = 5000 / 0.001 = 5,000,000:1.

When a Given Op-Amp Has 10 V Common-Mode Inputs, the Output