A differential amplifier has a differential gain of 20,000. CMRR = 80 dB. The common mode gain is given by
- A. 2
- B. 1
- C. 1/2
- D. 0
Answer: A. 2
Explanation: $CMRR_{dB} = 20 \log(\frac{A_d}{A_{cm}})$. $80 = 20 \log(\frac{A_d}{A_{cm}})$. $\frac{A_d}{A_{cm}} = 10^4 = 10000$. $A_{cm} = \frac{A_d}{10000} = \frac{20000}{10000} = 2$.