Question

For what type of signals does a transistor behaves as linear device?

(a) small signals only

(b) large signals only

(c) both large and small signal

(d) no signal

This question was addressed to me by my school teacher while I was bunking the class.

The above asked question is from Transistor Hybrid Model in chapter Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Correct choice is (a) small signals only

Explanation: The small variation in the total voltage and current due to an application of signal moves the point up and down just by a bit and that whole up and down dynamics of the operating point from its DC value point can be approximated to be along a straight line. Whole analysis can be done with same assumption of linearity with the limit of signal being in the same vicinity of the DC operating point.

That’s how we get all those equations for linear operation and also its small signal equivalent model using h-parameters.