Question

Consider the following circuit. __________ provides DC isolation.  _____________ prevents a decrease in voltage gain. _____________ is used to control the bandwidth.

(a) C3, C1, C4

(b) C4, C1, C2

(c) C2, C3, C2

(d) C4, C3, C2

This question was addressed to me by my college professor while I was bunking the class.

This intriguing question originated from Hybrid Equivalent Model in chapter Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

The correct choice is (b) C4, C1, C2

Easiest explanation: Capacitor C3 and C4, are the blocking capacitor and coupling capacitor respectively, both providing DC isolation to biasing circuit. Capacitor C1 is the emitter bypass capacitor, to prevent decrease in voltage gain by avoiding negative feedback. Capacitor C2 is the shunt capacitor, used to control the bandwidth, wherein the bandwidth is inversely proportional to C2.