Question

If the differential voltage gain and the common mode voltage gain of a differential amplifier are 48 db and 2 db respectively, then its common mode rejection ratio is

Answer 1

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Answer 2

Answer:

Common mode rejection ratio is $46dB$

Explanation:

The output voltage of op-amp is given by:

$V_{0}=A_{d} V_{d}+A_{c} V_{c}$

Where, $V_{d}=V_{1}-V_{2}$

$\begin{aligned}&V_{C}=\frac{V_{1}+V_{2}}{2} \\&\mathrm{~A}_{d}=\text { differential voltage gain }\end{aligned}$

$A_{c}=$ common-mode voltage gain

$C M R R=20 \log \left(\frac{A_{d}}{A_{c}}\right)$

$\underline{\text {Solution:}}$

Given,

Differential voltage gain $=48 \mathrm{~dB}$

Common mode voltage gain$=2 \mathrm{~dB}$

$\begin{aligned}&C M R R=20 \log \left(\frac{A_{d}}{A_{c}}\right) \\&C M R R=20 \log \left(\mathrm{A}_{d}\right)-20 \log \left(\mathrm{A}_{c}\right) \\&=48-2=46 \mathrm{~dB}\end{aligned}$