3.4 - ECE3080, Chapter 3.4 1 June 16, 2005 ECE 3080:...

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Unformatted text preview: ECE3080, Chapter 3.4 1 June 16, 2005 ECE 3080: Chapter 3.4 PN Junction O. Brand, 1 of 16 3.4 PN Junction: Dynamic Behavior 3.4.1 Small-Signal Admittance Equivalent Circuit Forward-Bias / Reverse-Bias Characteristics Depletion Layer Capacitance Diffusion Admittance 3.4.2 Transient Behavior Turn-Off Transient Storage Delay Time Pierret, Chapter 7 & 8, page 301-344 June 16, 2005 ECE 3080: Chapter 3.4 PN Junction O. Brand, 2 of 16 3.4.1 Small-Signal Admittance 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 ! C Pierret, Fig. 7.1 & 7.2 ECE3080, Chapter 3.4 2 June 16, 2005 ECE 3080: Chapter 3.4 PN Junction O. Brand, 3 of 16 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 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 June 16, 2005 ECE 3080: Chapter 3.4 PN Junction O. Brand, 4 of 16 Junction Capacitance The so-called junction or depletion- layer capacitance originates from charge oscillations at the edge of the depletion region caused by the applied ac voltage v a The capacitance resulting from the small oscillations of the depletion region around its steady-state width W is equivalent to that of a parallel plate capacitor with width W C j = dQ(V A ,v a ) dv a = K s ! A W(V A ) Pierret, Fig. 7.4 ECE3080, Chapter 3.4 3 June 16, 2005 ECE 3080: Chapter 3.4 PN Junction O. Brand, 5 of 16 Junction Capacitance C j Junction capacitance C j depends on the applied dc bias V...
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This note was uploaded on 08/28/2010 for the course ECE 3080 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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3.4 - ECE3080, Chapter 3.4 1 June 16, 2005 ECE 3080:...

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