Electronic Devices and Circuits
Engineering Sciences 154

BJT Large and Small Signal Models

Click on images to enlarge

Small signal equivalent circuits:
Popular equivalent circuit #1

Common emitter input resistance rp:
Popular equivalent circuit #2
Common base input resistance re:


Addition of output resistance: The Early effect - voltage induced base narrowing (see discussion of bias effect on depletion layer thickness in Lecture Set 2)

Early correction to collector current equation:
Output resistance:
Popular equivalent circuits modified to incorporate Early effect:

This page was prepared and is maintained by R. Victor Jones
Comments to: jones@deas.harvard.edu.

Last updated November 1,  2001