An OPAMP has a common mode gain of 0.01 and a differential mode gain of 105. Its common mode rejection ratio would be:

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ESE Electrical 2013 Paper 2: Official Paper
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  1. 10-7
  2. 10-3
  3. 103
  4. 107

Answer (Detailed Solution Below)

Option 4 : 107
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Detailed Solution

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Concept:

Common mode rejection ratio(CMRR): It is the “ratio of the differential voltage gain (Ad) to the common-mode voltage gain (Acm)”.

The higher the value of CMRR the better is the matching between two input terminals and smaller is the output common-mode voltage.

CMRR = \( \frac{{{A_d}}}{{{A_{cm}}}}\) 

It is infinity ∞  for the ideal op-amp.

Calculation:

Given that, common-mode gain = 0.01

Differential mode gain = 105

CMRR=\(\frac{{{{10}^5}}}{{0.01}}\) = 107.

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