Question

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

(a) -hib + (hfb × hib / YL + hob)

(b) hib – (hfb × hib / YL + hob)

(c) -hib + (hfb × hrb / YL + hob)

(d) hib – (hfb × hrb / YL + hob)

This question was posed to me during an online interview.

My doubt stems from Analysis of Transistor Amplifier Circuit using h-parameters topic in portion Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Right choice is (d) hib – (hfb × hrb / YL + hob)

The explanation: 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 base transistor amplifier in terms of hybrid parameters is expressed as hib – (hfb × hrb / YL + hob), where YL is the load admittance.