Question

Why do we require RE for a good stable alpha cutoff frequency?

(a) To obtain a current IE sensitive to α and VBE

(b) To obtain a current IB sensitive to α and VBE

(c) To obtain a current IE insensitive to α and VBE

(d) To obtain a current IB insensitive to α and VBE

This question was addressed to me in quiz.

This intriguing question comes from The Alpha Cutoff Frequency topic in portion High Frequency Transistor of Electronic Devices & Circuits

Answer 1

Right answer is (c) To obtain a current IE insensitive to α and VBE

To elaborate: The aim of having an alpha cutoff frequency is to maintain a stable current or voltage, regardless of other parameters changing. Hence, we need RE to get a stable IE current. Without RE the value of IE changes drastically with a small change in α.