Question

How many h-parameters of a transistor are dimensionless?

(a) Four

(b) Two

(c) Three

(d) One

This question was posed to me in an internship interview.

This is a very interesting question from Transistor Hybrid Model in division Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Right choice is (b) Two

For explanation: (i) H11 = V1/I1;   for V2 = 0 (output short circuited)

This parameter is input impedance with output short.

Its unit is ohm.

(ii) H21 = i2/i1;   for V2 = 0   (output short circuited)

This parameter is Current gain ratio with output short.

It is unit less or dimensionless.

(iii) H12 = V1/V2;    for i1 = 0   (input open circuited)

This is voltage gain feedback ratio with terminals open.

And it is unit less or dimensionless.

(iv)   H22 = i2/v2;    for i1 = 0   (input open circuited)

This is output admittance with input terminals open.

Its unit is ohm^-1 or mho.

Thus there are two h-parameters which are unit less or dimensionless.