GATE EE 2024 Set 1 — Question 61
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Analog & Digital Electronics → Operational Amplifiers → Op-Amp Non-Idealities
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Question
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).
Correct answer
39.5 to 41.5
Solution
For a difference amplifier with input resistors and feedback/ground resistors , the output voltage is given by:From the given circuit:
,
,
Let
Let
The output can be expressed in terms of differential mode voltage and common mode voltage :where
and
The Common Mode Rejection Ratio (CMRR) is:In dB:Using more precise values, .
,
,
Let
Let
The output can be expressed in terms of differential mode voltage and common mode voltage :where
and
The Common Mode Rejection Ratio (CMRR) is:In dB:Using more precise values, .
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