The GATE Grind

GATE 2025 IN – Question 41

Analog Electronics · Noise and interference · 2 marks · Multiple choice

The shown chopper amplifier processes a biomedical signal $v_{in}(t)$ into $v_{out}(t)$. Signals $v_{in}(t)$ and $v_{os}(t)$ are band limited to 50 Hz and 10 Hz, respectively. For linear-amplifier operation, choose the correct statement.

Diagram for GATE 2025 IN question 41
  1. The minimum frequency of $s(t)$ is 100 Hz; $v_{os}(t)$ is attenuated.
  2. The minimum frequency of $s(t)$ is 100 Hz; $v_{os}(t)$ is amplified by $200/\pi$.
  3. The minimum frequency of $s(t)$ is 80 Hz; $v_{os}(t)$ is attenuated.
  4. The minimum frequency of $s(t)$ is 80 Hz; $v_{os}(t)$ is amplified by $200/\pi$.

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Show answer and explanation

Correct answer: (A) The minimum frequency of $s(t)$ is 100 Hz; $v_{os}(t)$ is attenuated.

Explanation

The two multipliers use the same ±1 square wave, so the desired signal is restored because s²(t)=1.

The post-amplifier offset is chopped to odd harmonics and removed by the low-pass.

Its cutoff π/T corresponds to fs/2 Hz and must pass the 50 Hz signal, so fs≥100 Hz in the ideal limiting case.

Thus **A**.