Question

A differential amplifier with a common-mode input of 500 mV and a difference-mode input of 30 mV has an output of 5 mV due to the common mode input and 3 V due to difference-mode input. Find the difference-mode and the common-mode gains respectively.

• A. 0.01, 0.01
• B. 100, 0.01
• C. 100, 100
• D. 0.01, 100

Answer 1

The correct option is B 100, 0.01

Difference-mode gain

$A_d=\frac{v_0}{v_d}=\frac{3}{30\times {10}^{-3}}=100$

Common-mode gain

$A_c=\frac{v_0}{v_c}=\frac{5\times {10}^{-3}}{500\times {10}^{-3}}=0.01$