學科競賽chppt課件(編輯修改稿)
2025-02-15 09:13 本頁面
【文章內(nèi)容簡介】 For output loop ? Incremental values can be represented by ac signal iC + ? v BE T + ? v C E b e c i B BQBCC iiii ?? ????bQBCc iiii ????where ????QBCii? ? Is ac mentemitter current gain. I b I c + ? V be + ? b c e r π β I b V ce ( g m V π ) + ? V π so bc ii ??r?gm=? 1. Hybrid? Equivalent Circuit of BJT ? Hybrid? parameters are the ac parameters. ? They are related to the Qpoint. ? They are only use in the ac analysis. ? ? ib is currentcontrol current source (CCCS). ? The direction of ? ib is related to the ib. I b I c + ? V be + ? b c e r π β I b V ce ( g m V π ) + ? V π 2. HParameters Equivalent Circuit of BJT I b I c + ? v be + ? 1/h oe b c e h re v ce h ie h fe I b v ce + ? vbe= hieib+ hrevce ic= hfeib+ hoevce ? Units of four parameters are different， so called hybrid parameters. 0bbeie ec ?? VIVh Input resistance, when vce is short for ac signal。 AC current gain, when vce is short for ac signal； Voltage feedback ratio 反向電壓傳輸比 , vbe is open for ac signal。 Output admittance 輸出電導 , vbe is open for ac signal。 0bcfe ce ?? VIIh0cebere b ?? IVVh0cecoe b ?? IVIh2. HParameters Equivalent Circuit of BJT ?hre very small, 103?104, negligible. ?hie =rb+ r?≈r? . ?hoe can be calculate ro=1/hoe=VA/ICQ. VA=Vce Ro Very large, 100k?, negligible. We get simplified smallsignal equivalent circuit. I b I c + ? V be + ? b c e r π g m V π V ce + ? V π I b I c + ? V be + ? 1 /h oe b c e h re V ce h ie h fe I b V ce + ? + ? i B R C v O V BB i C V BE R B + ? V CC + ? V CE + ? v i SmallSignal Model Analysis 3. Circuit Analysis with SmallSignal Model (1) Find QPoint Values in DC Equivalent Circuit BBEBBB RVVI ??BC IβI ?CCCCCE RIVV ??3. Circuit Analysis with SmallSignal Model (2) SmallSignal Equivalent Circuit + i b R C v o i c v be R B ? + ? v ce + ? v i Th e ac Eq u iv alen t C ircu it I b R C I c g m V π + ? V i + ? V o r π R B b c e + ? V π The smallsignal equivalent circuit 3. Circuit Analysis with SmallSignal Model (3) Find the voltage gain )()( πBπππBbi rRrVrRIV ????CπmCco RVgRIV ????? Thus BππCmioRrrRgVVAv ????? Due to I b R C I c g m V π + ? V i + ? V o r π R B b c e + ? V π The smallsignal equivalent
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