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GATE 2025 EC – Question 30

Analog Circuits · BJT and MOSFET Amplifiers · 1 mark · Multiple select

Which of the following statements is/are TRUE with respect to ideal MOSFET-based DC-coupled single-stage amplifiers having finite load resistors?

  1. The common-gate amplifier has an infinite input resistance
  2. The common-source amplifier has an infinite input resistance
  3. The input and output voltages of the common-source amplifier are in phase
  4. The input and output voltages of the common-drain amplifier are in phase

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Correct answer: (B) The common-source amplifier has an infinite input resistance; (D) The input and output voltages of the common-drain amplifier are in phase

Explanation

An ideal MOSFET gate draws no current, so the common-source input resistance is infinite (B true). The common-gate input resistance is about $1/g_m$, which is finite (A false). The common-source stage inverts (C false). The common-drain (source-follower) output follows the input in phase (D true).