Question

Given VDD = 25V, VP = -3V. When VGS = -3V, IDS = 10mA. Find the operating point of the circuit.

(a) -3.83V, 0.766mA

(b) -2.345V, 0.469mA

(c) 3.83V, 0.469mA

(d) 2.3V, 0.7mA

This question was addressed to me during an interview.

I want to ask this question from Biasing of JFET and MOSFET topic in chapter FET Amplifiers of Analog Circuits

Answer 1

Right choice is (b) -2.345V, 0.469mA

Easiest explanation: When VGS = VP then IDSS = IDS = 10mA

Also, in above circuit, VGS = -IDSRS = – IDSx5k

Thus, IDS = IDSS(1-VGS/VP)^2

Solving we get, IDS = 0.766mA, 0.469mA

Thus we get VGS = -3.83V, -2.345V

However, VGS should lie between 0 and VP.