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GATE 2024 EE – Question 61

Analog and Digital Electronics · Operational amplifiers: characteristics and applications · 2 marks · Numerical answer

A difference amplifier is shown in the figure. Assume the op-amp to be ideal. The CMRR (in dB) of the difference amplifier is __________ (rounded off to 2 decimal places).

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Correct answer: 40.31 to 40.71

Explanation

The output is $v_o=-\dfrac{101}{10.5}v_{in1}+\left(1+\dfrac{101}{10.5}\right)\dfrac{101.5}{9.5+101.5}v_{in2}=-9.619v_{in1}+9.710v_{in2}$. The differential gain is $A_d=\dfrac{9.710+9.619}2=9.665$ and the common-mode gain is $A_c=9.710-9.619=0.0912$. So CMRR $=20\log\dfrac{9.665}{0.0912}=20\log106.0=40.51$ dB.