Question

Which of these is false for a CS amplifier without a bypass capacitor compared to a CS amplifier with a bypass capacitor?

(a) Voltage gain magnitude decreases

(b) Input resistance remains same

(c) The output resistance decreases

(d) The output is 180° out of phase with respect to the input applied

I have been asked this question at a job interview.

The origin of the question is JFET Amplifier in division FET Amplifiers of Analog Circuits

Answer 1

Correct answer is (c) The output resistance decreases

To explain: For a CS amplifier without a bypass capacitor, the input resistance is unchanged and output resistance increase.

RI = RG for both.

RO = rds with bypass capacitor and rds = rds + (1+μ) RS without a bypass capacitor.

Output is still 180° out of phase compared to applied input, but the gain decreases.