signal amplification; design of digital logic; memory circuits

Transcription

1 hatr Th lctroc dvc that s caabl of currt ad voltag amlfcato, or ga, cojucto wth othr crcut lmts, s th trasstor, whch s a thr-trmal dvc. Th dvlomt of th slco trasstor by Bard, Bratta, ad chockly at Bll Tlho Laborators th lat 190s startd th frst lctrocs rvoluto of th 1950s ad 1960s. Ths vto ld to th dvlomt of th frst tgratd crcut 1958 ad to th oratoal trasstor amlfr, whch s o of th most wdly usd lctroc crcuts. BJTs ar thr-trmal smcoductor dvcs, whch ar far mor usful tha twotrmal os bcaus thy ca b usd a multtud of alcatos such as sgal amlfcato; dsg of dgtal logc; mmory crcuts Thr ar two major tys of thr-trmal smcoductor dvcs: th bolar jucto trasstor (BJT), whch s th subjct of ths chatr, ad th fld-ffct trasstor (FT). Th two trasstor tys ar qually mortat, ad ach offrs dstct advatags ad has uqu aras of alcato:

2 s show Fg..1, th BJT cossts of thr rgos: Th mttr (-ty), th bas ( ty) ad th collctor ( ty). uch a trasstor s calld a trasstor. s show Fg.., th BJT cossts of thr rgos: Th mttr (-ty), th bas ( ty) ad th collctor ( ty). uch a trasstor s calld a trasstor.

3 Ddg o th bas codto (forward or rvrs) of ach of ths juctos, dffrt mods of orato of th BJT ar obtad. Th actv mod s th o usd f th trasstor s to orat as a amlfr. wtchg alcatos (for xaml, logc crcuts) utlz both th cutoff ad th saturato mods. Th rvrs-actv or vrtd mod s smlar to th forward-actv mod wth a sgfcat dffrc that th currt ga (to b dscussd) s much smallr comard to that of forward actv cas, whch maks ths mod usutabl for amlfcato. Howvr, th vrtd mod has alcato dgtal crcuts ad crta aalog swtchg crcuts.

4 Th urrt Flow Udr th bas arragmt show Fg.., trasstor works th actv mod. Th forward bas o th mttrbas jucto wll caus mttr currt cosstg of two comots: lctros jctd from th to B (Largr Porto) Hols jctd from th B to (mall Porto) Du to a havly dod mttr ad a lghtly dod bas. Thos lctros wll b morty carrrs th -ty bas rgo. Thy ar vry dffcult to rach to th othr sd of th B. Th lctro coctrato wll b hghst ( (0)) at th mttr sd ad lowst (zro) at th collctor sd. Bcaus of th th bas, th coctrato dstrbuto s a lar dcay.

5 Th urrt Flow (cot.) osdrg th law of th jucto of ay forward-basd jucto, w hav ( 0) 0 v B / V T whr 0 s th thrmal qulbrum valu of th morty-carrr (lctro) coctrato th bas rgo, V T s th thrmal voltag (5 mv at room tm.) Th tard morty-carrr coctrato rofl causs th lctros jctd to th bas to dffus through B rgo toward th. Th lctro dffuso currt s formd: d dx ( x) ( (0) ) W

6 Th urrt Flow (cot.) Bcaus th collctor s mor ostv tha th bas (by v B volts), th major orto of th dffusg lctros rachg th boudary of th collctor-bas dlto rgo wll b swt across th BJ dlto rgo to th collctor. Thus c / V whr th saturato currt ubsttut g v B T / W / N trsc carrr dsty, N, 0 0 whr s th dog coctrat o of th bas, w hav s gv by s th /( N W )

7 Th urrt Flow (cot.) mortat Facts: t ca b obsrvd that s ddt of v B, as log as th collctor s ostv wth rsct to th bas. s vrsly roortoal to th bas wdth W ad s drctly roortoal to th ara of BJ. Thrfor, s rfrrd to as currt scal factor. Ths coct s frqutly mloyd tgratd crcut dsg. Bcaus s roortoal to, t s a strog fucto of tmratur, aroxmatly doublg for vry 5 o rs tmratur.

8 Th Bas urrt Th bas currt B s comosd of two comots: (1) B1 du to th hols jctd from B to th () B du to th hols that hav to b suld by th xtral crcut ordr to rlac th hols lost from th bas through th rcombato rocss. Q B τ b qw N v B / V T Th total bas currt B ca b xrssd as B1 N D L v B / V T B D ( D N N D W L + W D τ b ) v B / V T β Not that v B / V T

9 Th mttr urrt vrtu of KL, ad that B w hav β + + B β ltratvly, α whr th costat a s rlatd to b by β α β + 1 or β α 1 α c s vry clos to but s lss tha, a s a costat that s lss tha but vry clos to 1. For stac, f b 100, th a s about β s calld th commo-mttr currt ga. mall chags α corrsod to vry larg chags β. α s calld th commo-bas currt ga. vry small chag B wll caus a larg chag. Ths s th basc rcl of amlfcato.