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GATE 2019 EE – Question 43

Analog and Digital Electronics · Amplifiers: biasing, equivalent circuit and frequency response · 2 marks · Multiple choice

The enhancement type MOSFET in the circuit below operates according to the square law. $\mu_nC_{ox}=100\ \mu\text{A/V}^2$, the threshold voltage ($V_T$) is 500 mV. Ignore channel length modulation. The output voltage $V_{out}$ is

Diagram for GATE 2019 EE question 43
  1. 100 mV
  2. 500 mV
  3. 600 mV
  4. 2 V

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Show answer and explanation

Correct answer: (C) 600 mV

Explanation

The transistor is diode-connected, so it is in saturation with the 5 $\mu$A source current: $5\ \mu\text{A}=\frac12(100\ \mu\text{A/V}^2)(10)V_{ov}^2$, which gives $V_{ov}^2=0.01$ and $V_{ov}=0.1$ V. Then $V_{out}=V_{GS}=0.5+0.1=0.6$ V.