The GATE Grind

GATE 2022 EC – Question 20

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

The ideal long channel nMOSFET and pMOSFET devices shown in the circuits have threshold voltages of 1 V and −1 V, respectively. The MOSFET substrates are connected to their respective sources. Ignore leakage currents and assume that the capacitors are initially discharged. For the applied voltages as shown, the steady state voltages are ________.

Diagram for GATE 2022 EC question 20
  1. $V_1=5$ V, $V_2=5$ V
  2. $V_1=5$ V, $V_2=4$ V
  3. $V_1=4$ V, $V_2=5$ V
  4. $V_1=4$ V, $V_2=-5$ V

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Show answer and explanation

Correct answer: (C) $V_1=4$ V, $V_2=5$ V

Explanation

The nMOSFET with gate at 5 V charges its capacitor until $V_{GS}=V_T$, i.e. until $V_1=5-1=4$ V (an nMOSFET passes a weak high). The pMOSFET has its gate at $-5$ V, so $V_{SG}=5-(-5)=10$ V stays well above 1 V while the capacitor charges to the full 5 V (a pMOSFET passes a strong high), so $V_2=5$ V.