small signal low frequency AC models of transistors


Joined Nov 25, 2009
What you are talking about, is a very large portion of the transistor theory.

Take a look here for the hybird-pi model:

The purpose of the small signal transistor models is to help us approach the circuit operation as far as the signal is concerned and calculate important parameters such as Input Resistance, Voltage Gain, Current Gain, Output resistance etc.

These should not be confused with the bias conditions calculations. Bias conditions refer to the biasing point at which we drive the transistor in order to achieve certain characteristics (mainly the dc collector current). On top of these conditions we apply the small signal (the important information we want amplified), and in order to analyse the signal course through our circuit, we utilize the small signal model.

Sedra/Smith's Microelectronic Circuits has helped me alot in the transistor field. It's a heavy read but it's worth it in my opinion.