Lecture 30 - BJT Dynamic Response

Lecture 30 - BJT Dynamic Response - BJT Dynamic Response...

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1 EE360 – Lecture 30 BJT Dynamic Response Objective: To understand how the BJT responds to signals that change with time. Questions to be answered: • What is the hybrid-pi model for the small signal response? • How can the BJT operate as a switch? EE360 – Lecture 30 Ebers-Moll Model: Review Equivalent Circuit C E B kT qV R kT qV F F C kT qV R R kT qV F E I I I e I e I I e I e I I CB EB CB EB = = = ) 1 ( ) 1 ( ) 1 ( ) 1 ( / 0 / 0 / 0 / 0 α Terminal Currents () + = + = B B B B B C C C R B B B B B E E E F L W L W p L D n L D qA I L W L W p L D n L D qA I sinh cosh sinh cosh 0 0 0 0 0 0 0 0 and R F dc R dc F I I = = Parameters From Pierret, pg. 404.
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2 EE360 – Lecture 30 Hybrid-Pi Model: Small-Signal A.C. Response • Common emitter, forward active mode • assume that transistor operates quasi-statically • Obtained directly from the Ebers-Moll model by taking the base-emitter voltage to be V BE + v be ( t ). • Total collector current = I C + i c (t). •r π = input resistance, g m = transconductance • Be careful with the signs Low-frequency model. No base- width modulation From Pierret, pg. 447.
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Lecture 30 - BJT Dynamic Response - BJT Dynamic Response...

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