Question

What is the role of input capacitance in the transistor amplifying circuit?

(a) To prevent input variation from reaching output

(b) To prevent DC content in the input from reaching transistor

(c) There isn’t any role for input capacitance

(d) To increase input impedance

I got this question in an interview for job.

This is a very interesting question from Characteristics of Amplifier in chapter Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

The correct option is (b) To prevent DC content in the input from reaching transistor

Best explanation: The input capacitance, as its name indicates is used to prevent DC offset voltages in the input. It also prevents the transistor bias voltage to be fed back to input generating circuit.