Electronic Devices and Circuits Engineering Sciences 154

First look at the so called Ebers-Moll (EM) Model (see also slide 33 of the Technische Universität Darmstadt slide set).

Click on images to enlarge (source)

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Small signal equivalent circuits:

Popular equivalent circuit #1

Transconductance:

Common emitter input resistance r_p:

Popular equivalent circuit #2

Common base input resistance r_e:

 

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

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Early correction to collector current equation:

Output resistance:

 
Popular equivalent circuits modified to incorporate Early effect: