Question

How the input impedance of a common collector transistor amplifier expressed in terms of transistor hybrid parameters?

(a) hic + (hfc × hrc / YL + hoc)

(b) hic – (hfc × hrc / YL + hoc)

(c) -hic + (hfc × hrc / YL + hoc)

(d) -hic – (hfc × hrc / YL + hoc)

The question was asked by my college director while I was bunking the class.

My question is taken from Analysis of Transistor Amplifier Circuit using h-parameters topic in section Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

The correct answer is (b) hic – (hfc × hrc / YL + hoc)

To elaborate: The input impedance of a transistor amplifier circuit is expressed as V1 / I1. This can be expressed in terms of transistor hybrid parameters. The input impedance of a common collector transistor amplifier in terms of hybrid parameters is expressed as hic – (hfc × hrc / YL + hoc), where YL is the load admittance.