Draw small signal hybrid π equivalent circuit for npn transistor.

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written 3.3 years ago by

teamques10 ★ 66k

A small signal resistance$rπ$ is defined as,$rπ = {Vbe\over Ib}$
Alternate equation for$rπ$ is$rπ = {Vbe\over IBQ}={βFVT\over ICQ}$
$rπ$ is called as diffusion resistance or base emitter input resistance.Note that value of resistance is depends on Q-point parameters.
At output side of transister is denoted by the current source as$gmVbe$,where gm is transconductance of the transistor which is define as;
$gm = {ICQ \over VT}$
Small signal transconductance is also function of a Q-point and directly proportional to the dc bias current.

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