Question

A transistor has hie =2kΩ, hoe=25µmhos and hfe=60 with an unbypassed emitter resistor Re=1kΩ. What will be the input resistance and output resistance?

(a) 90kΩ and 50kΩ respectively

(b) 33kΩ and 45kΩ respectively

(c) 6kΩ and 40kΩ respectively

(d) 63kΩ and 40kΩ respectively

I got this question in an interview for job.

I would like to ask this question from The AC Analysis of a Small-Signal Low-Frequency Common Emitter Transistor. topic in chapter Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Right option is (d) 63kΩ and 40kΩ respectively

The explanation is: As the emitter is unbypassed, the input resistance Ri=hie+(1+hfe)Re

=2+61=63kΩ. The output resistance RO=1/hoe=1/25MΩ=40kΩ.