Question

Which among the following will possess a higher bandwidth, if two transistors are provided with unity gain frequency?

(a) Transistor with lower hfe

(b) Transistor with higher hfe

(c) Transistor with lower hre

(d) Transistor with higher hre

I have been asked this question in a national level competition.

My question is taken from Frequency Compensation topic in division Frequency Response of Electronic Devices & Circuits

Answer 1

Correct answer is (a) Transistor with lower hfe

Easy explanation: In general, the short circuit CE gain of a transistor gets reduced to unity at f = fT. This implies that the transistor loses its capability of current amplification at f = fT.

As the gain-bandwidth product always remains constant, the transistor with lower hfe will definitely possesses higher bandwidth if the two transistors are made available with equal unity gain frequency.