Unit 3: Transistor at Low Frequencies

Transcription

1 Unt 3: Tansst at Lw Fquncs JT Tansst Mdlng mdl s an qualnt ccut that psnts th chaactstcs f th tansst. mdl uss ccut lmnts that appxmat th ha f th tansst. Th a tw mdls cmmnly usd n small sgnal analyss f a tansst: mdl Hyd qualnt mdl Th Tansst Mdl JTs a ascally cunt-cntlld dcs; thf th mdl uss a dd and a cunt suc t duplcat th ha f th tansst. On dsadantag t ths mdl s ts snstty t th D ll. Ths mdl s dsgnd f spcfc ccut cndtns. mmn-as nfguatn

2 c α nput mpdanc: 26 m Output mpdanc: Ω ltag gan: unt gan: L α α 1 L mmn-mtt nfguatn Th dd mdl can placd y th sst. ( ) 1 26 m mmn-mtt nfguatn

3 nput mpdanc: Output mpdanc: Ω ltag gan: unt gan: L mmn-llct nfguatn nput mpdanc: ( 1) Output mpdanc: ltag gan: unt gan: 1

4 Th Hyd qualnt Mdl Th fllwng hyd paamts a dlpd and usd f mdlng th tansst. Ths paamts can fund n th spcfcatn sht f a tansst. h nput sstanc h s tansf ltag at ( / ) 0 h f fwad tansf cunt at ( / ) h utput cnductanc Smplfd Gnal h-paamt Mdl h nput sstanc h f fwad tansf cunt at ( / )

5 s. h-paamt Mdl mmn-mtt h h f ac mmn-as h h f α 1 Th Hyd p Mdl Th hyd p mdl s mst usful f analyss f hgh-fquncy tansst applcatns. t lw fquncs th hyd p mdl clsly appxmat th paamts, and can placd y thm. mmn-mtt Fxd-as nfguatn Th nput s appld t th as Th utput s fm th cllct Hgh nput mpdanc Lw utput mpdanc Hgh ltag and cunt gan Phas shft twn nput and utput s 180

6 10 O ) ( 10, 10 ) )( ( mmn-mtt Fxd-as nfguatn mmn-mtt Fxd-as alculatns nput mpdanc: ltag gan: Output mpdanc: unt gan:

7 unt gan fm ltag gan: mmn-mtt ltag-dd as mdl qus yu t dtmn,, and. alaculatns: nput mpdanc: Output mpdanc: ltag gan:

8 10, ) )( ( ) ( 1) ( unt gan: unt gan fm ltag gan: mmn-mtt mtt-as nfguatn mpdanc alculatns nput mpdanc: Output mpdanc:

9 ) ( Gan alculatns ltag gan: unt gan: unt gan fm ltag gan: mtt-fllw nfguatn Ths s als knwn as th cmmn-cllct cnfguatn. Th nput s appld t th as and th utput s takn fm th mtt. Th s n phas shft twn nput and utput.

10 >> ) ( 1) (, 1 >> mpdanc alculatns nput mpdanc: Output mpdanc: Gan alculatns ltag gan: unt gan:

11 unt gan fm ltag gan: mmn-as nfguatn Th nput s appld t th mtt. Th utput s takn fm th cllct. Lw nput mpdanc. Hgh utput mpdanc. unt gan lss than unty. y hgh ltag gan. N phas shft twn nput and utput. alculatns nput mpdanc:

12 Output mpdanc: ltag gan: α unt gan: α 1 mmn-mtt llct Fdack nfguatn Ths s a aatn f th cmmn-mtt fxd-as cnfguatn nput s appld t th as Output s takn fm th cllct Th s a 180 phas shft twn nput and utput alculatns nput mpdanc: 1 F

13 F F F F Output mpdanc: ltag gan: unt gan: llct D Fdack nfguatn Ths s a aatn f th cmmn-mtt, fxd-as cnfguatn Th nput s appld t th as Th utput s takn fm th cllct Th s a 180 phas shft twn nput and utput

14 F 1 F F F F alculatns nput mpdanc: Output mpdanc: ltag gan: unt gan: Tw-Pt Systms ppach

15 Ths appach: ducs a ccut t a tw-pt systm Pds a Thénn lk at th utput tmnals Maks t as t dtmn th ffcts f a changng lad Wth st t 0 : Th Th ltag acss th pn tmnals s: wh NL s th n-lad ltag gan. Th NL ffct f Lad mpdanc n Gan Ths mdl can appld t any cunt- ltag-cntlld amplf. ddng a lad ducs th gan f th amplf: L L NL L

16 s s NL s s s L L NL L ffct f Suc mpdanc n Gan Th factn f appld sgnal that achs th nput f th amplf s: Th ntnal sstanc f th sgnal suc ducs th all gan: mnd ffcts f S and L n ltag Gan ffcts f L :

17 ffcts f L and S : s s s s s s L L L NL ascadd Systms Th utput f n amplf s th nput t th nxt amplf Th all ltag gan s dtmnd y th pduct f gans f th nddual stags Th D as ccuts a slatd fm ach th y th cuplng capacts Th D calculatns a ndpndnt f th cascadng Th calculatns f gan and mpdanc a ntdpndnt - upld JT mplfs nput mpdanc, fst stag: Output mpdanc, scnd stag: 2 1

18 ltag gan: