Lecture 7. Large and Small Signal Modelling of PN Junction Diodes

Transcription

1 ecture 7 are a Small Sal Moell of PN Jucto oes ths lecture you wll lear: Crcut moels of PN jucto oes Small sal moel of olear crcut elemets Small sal moels of PN jucto oes Jucto resstace a cataces Curret Flow a PN Jucto oe Area A a o q o T N N A q e AJ coth coth coth coth q a T e N N q J Jucto breakow everse bas Forwar bas ON

2 Smlest Crcut Moel for a PN Jucto oe oa e: For most oes: 0.4 ON 0.8 Sloe ON Soluto for curret: f ON : f > ON : 0 ON ON Better Crcut Moel a PN Jucto oe Sloe ON

3 Crcut Examle for a PN Jucto oe oa e: Sloe ON Soluto for curret: f ON : f > ON : ON 0 ON ear Crcut Elemets Ohm s aw: Sloe = G G Ohm s law mles a NEA relatosh betwee curret a voltae + - G The curret-voltae relatosh of resstors s lear 3

4 Nolear Elemet: Nolear Crcut Elemets Curret s a fucto of the voltae (but the curret-voltae relatosh s ot lear) + - For examle: C A Be The curret-voltae relatosh of most evces s ot lear! Small Sal Moel of Nolear Crcut Elemets t BAS BAS Bas ot BAS BAS v t BAS t BAS BAS v t BAS 4

5 BAS Small Sal Moel of Nolear Crcut Elemets Taylor exa the curret-voltae relato arou the bas voltae: BAS t t BAS v t BAS t BAS BAS v t v t... BAS t v t v BAS BAS v t t BAS Assume small BAS r Sloe = v t BAS fferetal resstace or fferetal couctace cremetal resstace or cremetal couctace Small Sal Moel of Nolear Crcut Elemets Comlete crcut s: t v t t Sloe = BAS t v t BAS BAS BAS v t Small sal equvalet crcut s: t v t r t v t small sal moels, olear crcut elemets are rele by ther learze moels that are val over a lmte rae of excurso arou the bas ot 5

6 A ffcult roblem: Small Sal Moel of Nolear Crcut Elemets BAS BAS t Sloe = BAS Bas ot BAS v t C C oa e: C BAS BAS C BAS BAS r A smler roblem: BAS v t t Small Sal Moel of a PN Jucto oe: Jucto Couctace P-oe + v N-oe N q e o q v e o v... v v q q q q o e o r Sloe = fferetal resstace stro forwar bas fferetal couctace 6

7 Small Sal Moel of a PN Jucto oe: Jucto Couctace P-oe + v N-oe N v v r q v Small sal crcut moel of a PN oe Small Sal Moel of a PN Jucto oe: Jucto eleto Catace x 0 x P-oe + v N-oe N At hh frequeces, art of the curret flows throuh the jucto but art of t also chares u the jucto catace v v C sa C j j t x x r C j v 7

8 Small Sal Moel of a PN Jucto oe: ffuso Catace P-oe + v N-oe N There s also chare store the quas-eutral reos that chaes as the jucto voltae s vare (eatve a ostve chare store at the same locato!!) x Chare store: ' x ' x x ' x ' x Morty carrers 0 x x x Majorty carrers Q qa x ' x x x qa x ' x x x Small Sal Moel of a PN Jucto oe: ffuso Catace P-oe Chare store: + ffuso Catace: C Q q A e q qa C N a x ' x Q x x x qa ' x cosh N sh creases exoetally wth bas! v x x cosh sh N-oe N 8

9 Small Sal Moel of a PN Jucto oe: Total Catace P-oe + v N-oe N At hh frequeces, art of the curret flows throuh the jucto but art of t also chares u the jucto catace a the ffuso catace v C j v C t C r C j v Cataces of a PN Jucto oe Total Catace: C C j C C r C j v 9

10 Small Sal Moel of a PN Jucto oe evere Bas C r 0 q o 0 C j v Breaboar r: Goo r 0

11 Breaboar r: Ba r