Chapter33_PN-Dynamic

Chapter33_PN-Dynamic - 3.3 PN Junction: Dynamic Behavior...

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3.3 PN Junction: Dynamic Behavior Small-Signal Analysis Equivalent Circuit Forward-Bias / Reverse-Bias Characteristics Depletion Layer Capacitance Diffusion Admittance Pierret, Chapter 7, page 301-324 Slides courtesy of Prof. Oliver Brand

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2 Small-Signal Analysis – Equivalent Circuit – AC current i flowing through the diode biased by small AC voltage v a superimposed on DC bias V A Small-signal admittance Y consists of capacitive C and conductive G component: Equivalent circuit of diode consists of junction admittance Y and series resistance R s of quasineutral regions Y = i/ v a = G + j ω C Pierret, Fig. 7.1 & 7.2
3 PN Junction: Small-Signal Behavior (a) Reverse Bias Small signal behavior is dominated by junction or depletion- layer capacitance C j The junction capacitance C j arises from majority carrier (charge) oscillations at the edges of the depletion region Conductance is very small (i.e., very high resistance) (b) Forward Bias With increasing forward bias, the diffusion admittance Y d = G d + i X C d dominates the small signal behavior The diffusion capacitance C d arises from minority-carrier (charge) oscillations in the quasineutral regions adjacent to the depletion region

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4 Junction Capacitance The so-called junction or depletion-layer capacitance originates from charge oscillations at the edge of the depletion
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This note was uploaded on 10/12/2011 for the course ECE 3040 taught by Professor Hamblen during the Fall '07 term at Georgia Institute of Technology.

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Chapter33_PN-Dynamic - 3.3 PN Junction: Dynamic Behavior...

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