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GATE 2026 BM – Question 55

Analog and Digital Electronics · Operational Amplifiers · 2 marks · Multiple select

In the ideal instrumentation amplifier shown, one input-stage feedback resistor R* differs slightly from the other input-stage resistors R. Which statements are true?

Diagram for GATE 2026 BM question 55
  1. Mismatch introduces a gain error
  2. Mismatch degrades common-mode rejection ratio
  3. Mismatch introduces an offset error
  4. Vout is insensitive to resistor mismatch

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Show answer and explanation

Correct answer: (A) Mismatch introduces a gain error; (B) Mismatch degrades common-mode rejection ratio

Explanation

One input amplifier has gain two while the other has gain 1+R*/R. Their mismatch changes the differential gain and prevents identical common-mode inputs from producing identical first-stage outputs. The difference stage then converts some common-mode signal into output, degrading CMRR. Ideal op-amps with both inputs zero still give zero output, so mismatch alone creates no input-independent offset. Select A,B.

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