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Draw small signal hybrid π equivalent circuit for npn transistor.

written 3.5 years ago by teamques10 ★ 68k

engineering physics

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written 3.5 years ago by teamques10 ★ 68k

1. The small Signal resistance$rπ$.
2. A dependent current source$gmVbe$.

• 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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