Chng 4 MCH KHUCH I TN HIU NH

Chng 4 MCH KHUCH I TN HIU NH DUNG BJT I. INH NGHIA - Khuch i l qu trnh bin i mt i lng (dng in hoc in p) t bin nh thnh bin ln m khng lm thay i dng ca n. 1 Khi xet BJT hot ng di iu kin tin hiu nh (s thay i ca tin hiu vo nh) th c th xem BJT nh mt b khuch i ac. I,V I,V in B KHUCH I out

2 - li l ti s ca mt lng tin hiu (dng in hoc in p) thay i ngo ra v ngo vo. Ky hiu l Ai hoc AV. + li dong: I out i o (rms ) Ai I in i i (rms ) + li ap: Vout v o (rms ) Av Vin v i (rms ) 3 Pout AP A v . A i

+ li cng sut: Pin A > 1: b khuch i tin hiu. A < 1: b suy giam tin hiu. Nhc li: + gia tri rms: tri hiu dung ( tinh cho tin hiu ac). + gia tri amp: tri bin (hoc inh peak). (amp ) (rms ) 2 4 in tr ngo vao cua mt b khuch i la tng tr tng ng ti cac u ngo vao cua no. Vin R in ( DC) I in v in rin (ac) i in 5

Cng sut ngo vao ac Pin v in (rms ) * i in (rms ) 2 in v (rms ) rin i in2 (rms ) * rin inh nghia tng t cho in tr va cng sut ngo ra. 6 nh hng cua in tr ngun i vi mch khuch i A vo rin Av v s rs rin vo

A v v in v in rin vs rs rin 7 * Khuch i ap - in ap vao b K: rin . v s v in rs rin in ap ra : v out rin . v s A v .v in A v . rs rin

co li ap la Av cang ln th rin >>rs . 8 * Khuch i dong rs i in is rs rin io rs Ai i s rs rin 9 - Dong ngo vao b K: rs .i s i in rs rin Dong ngo ra :

i out rs .i s A i .i in A i . rs rin co li dong la Ai cang ln th rs >>rin . 10 nh hng cua in tr tai - Mt b khuch i ac dng cung cp ap, dong hoc/va cng sut cho mt tai ngo ra. - Tai co th la loa, anten, coi, ng c in hoc bt k 1 thit bi hu ich nao. - Khi phn tich mch nay, ta thay th bng 1 in tr tai RL. 11 p ra trn tai: rL . v out

v L ro rL co ap ri ti a trn tai th rL>>ro. Xt ca anh hng cua ngun th li ap t ngun n tai: rin vL A V . vs rs rin rL . ro rL 12 Mt cach tng t khi xt n b khuch i dong, ta co: Dong trn tai:

ro .i out i L ro rL li dong tng: rs ro iL . A i . is rs rin ro rL co dong ti a trn tai th ro>>rL. 13 truyn cng sut cc i th cn co s phi hp tr khang: - T ngun tin hiu n b khuch i: rs = r in. - T b khuch i n tai: rout = rL. 14 Muc ich phn cc DC Khi thit k phn cc cho BJT ng thi cng

l chn im lm vic cho BJT. Khi , dng sng ngo ra s ph thuc vo gi tr im phn cc v s thay i ca tin hiu ngo vo. vo(t) = VB + vin VB: p phn cc tnh 15 Vmax(maximum output valtage): l gi tr max ngo ra khi BJT khng dn gi l p ct (cutoff), thng bng p ngun cung cp. Vmin(minimum output valtage): l gi tr min ngo ra khi BJT dn bo ha. 16 Ty thuc vo gi tr ca VB m in p ra s c nhng thay i nh sau: 17 Ch Maxswing L ch hot ng khi p ngo ra t gi tr ti a m khng b meo dng tin hiu. t c ch ny th im phn cc tnh phi c chn nm gia gi tr Vmin Vmax.

VO Vmax VB Vmin t 18 Tu ghp -Tinh cht ca t l ngn tin hiu DC, thng thng t s c dng ngn nh hng ca tin hiu DC i vi ngun hoc ti. - Cc t ny phi ln c tng tr tht nh i vi tin hiu AC. - Cc t ny c gi l t ghep (coupling capacitor) hoc t chn (blocking capacitor). 19 20 ng tai mt chiu va ng tai xoay chiu VCC RC

RB RC RL Xet mch khuch i CE: - in tr ti DC: RL = RC. - in tr ti AC: rL = RL // RC. 21 - ng tai DC l tp hp tt c cc im lm vic tnh Q(IC,VCE), khi cha c tin hiu AC. - ng tai AC l tp hp tt c cc im (iC,vCE), bao gm c im Q. 22 - Phng trnh ng ti AC: VQ io IQ rL v o VQ I Q rL IQ, VQ = Q(IC,VCE)

iO, vO:gi tr iC v vCE ca ng ti AC. 23 Nhn xet 1 - ng ti AC c dc ( tg ) ln hn rL 1 ng ti DC (tg ). RL - p ngo ra c quyt nh bi ng ti AC s nh hn nu c quyt nh bi ng ti DC. - Nu Q dch trn ng ti DC th ng ti AC s dch song song. 24 25 IC (I C Q

VCEQ ) rL ACLL Q(VCE,IC) ICQ VCEQ DCLL (VCEQ+ ICQ.rL) VCE i vi bi ton a thit k sn th gi tr maxswing(ly tng) ca vout l: vout= min[(0VCEQ),(VCEQVCEQ+ICQrL)] 26

II. CC CH LM VIC CA BJT TRONG MCH iC KHUCH I Ch A (Lp A) Khi chn im Q nm khong gia on MN trn ng ti xoay chiu, ta ni phn t K lm vic ch A. c im ca ch ny l: IBmax C iCmax M iCQ Q N

iCmin vCEQ IBmin VCE D - Khuch i trung thc, it mo phi tuyn. - Dong va ap tinh lun khac khng. Bin dong va ap xoay chiu ly ra ti a chi bng dong va ap tinh. Do o hiu sut thp (25%). 27 inh nghia hiu sut : o bng t s gia cng sut cua tin hiu xoay chiu a ra trn tai va tng cng sut tng khuch i tiu thu cua ngun cung cp. Ch A thng dng trong cac tng khuch i tin hiu nh. Ch B (Lp B) Khi chn im Q nm trng vi D (hoc N) th phn t khuch i lm vic ch B ly tng (hoc thc t). c im ca ch ny l: - Mo phi tuyn trm trng. - Hiu sut cao. (Bmax = 78.5%).

- Thng dng trong cac tng khuch i cng sut (tng cui cua cac thit bi khuch i). khc phuc mo phi tuyn, oi hi mch phai co 2 v i xng thay phin lam vic trong 2 na chu k (gi la mch y ko). 28 Thc t, ngi ta cn dng ch AB (trung gian gia ch A va B): im Q chn phia trn im N v gn im ny. Lc pht huy c u im ca mi ch , gim bt meo phi tuyn, nhng hiu sut kem hn ch B. Ch khoa hay ch ong ngt (lp D) BJT c th lm vic ch ng ngt (Switch BJT). Tu theo gi tr in p vo m BJT c th lm vic 2 trng thi i lp: -Trng thi kha (tt): khi Q nm phia di im N. - Trng thi dn bo ha (m): khi Q nm phia trn im M (gn im C). 29 III. S TNG NG CA BJT - Mc ich ca vic chuyn v s tng ng l lm cho mch tinh ton n gin v d dng hn. - Khi s bin thin tin hiu vo nh to s thay i v dng v p ngo ra nm trong c tinh gii hn ca BJT, ta c th xem BJT l mt phn t 4 cc tuyn tinh:

I1 V1 I2 V2 I1, V1(i1, v1): dng v p ngo vo. I2, V2(i2, v2): dng v p ngo ra. 30 Tham s xoay chiu cua BJT Tu theo tng s c th ca BJT (BC, EC hay CC) th cc i lng trn s l nhng in p hay dng in trn cc cc tng ng, ng thi ty theo loi BJT( NPN hay PNP) m chng c du hoc chiu thich hp. Tu theo vic chn bin v hm m t mi quan h gia cc ngo vo v ra ca BJT m ta c cc loi tham s c trng cho BJT. Bin I1, I2 V1,V2

I1,V2 V1,I2 V2,I2 V1,I1 Hm V1,V2 I1,I2 V1,I2 I1,V2 V1,I1 V2,I2 Tham s z Tham s y Tham s h 31 B tham s h

V1 V1 dV1 I dI 1 V dV2 1 2 dI I 2 dI I 2 dV 2 1 2 I1 V2 V1 = f(I1,V2) I2 = f(I1,V2) v1 = h11i1 + h12 v2 i2 = h21i1 + h22 v2 ngha ca tng tham s

Tr khang vao cua BJT khi ap xoay chiu v1 h11 (hi ) ngo ra bi ngn mch. i 1 V2 0 i2 h 21 (hf ) i1 i2 h 22 (ho ) v2 v1 h12 (hr ) v2 V2 0 H s khuch i dong in ( li dong) cua BJT khi ap xoay chiu ngo ra bi ngn mch. in dn ra cua BJT khi dong xoay chiu ngo vao bi h mch. I 1 0

I 1 0 H s truyn ngc v in ap (hi tip in ap) cua BJT khi dong xoay chiu ngo vao bi h mch. 32 - V vy, phm cht, tinh nng ca BJT s th hin gi tr cc tham s hij ca chng. - Cc hij c gi l cc tham s xoay chiu (hoc tham s vi phn) ca BJT. - V n v o: - h11(hoc hi): in tr (). - h22(hoc ho): in dn (mho ( ) hoc siemient). - h12(hoc hr) v h21(hoc hf) chi l cc h s nn khng c th nguyn. Do , b tham s hij cn c gi l tham s hn hp (hybrid). - Ty theo BJT mc theo kiu no (BC, EC hay CC) m cc 33 tham s c thm chi s tng ng. Mch tng ng cua BJT

i1 v1 = h11i1 + h12 v2 i2 = h21i1 + h22 v2 v1 i2 h11(hi) h12v2 h21i1 1 h 22 v2 - in tr vo h11 (hoc hi). -Ngun in p h12v2 (hoc hr vo): th hin s hi tip in p ni b ca BJT. Thc t h12 (hay hr) c gi tr rt be(10-3 10-4), v vy i lng h12v2 c th b qua. - Ngun dng in h21i1(hoc hfii): phn nh kh nng khuch i dng.

- in dn ra h22(hoc ho), thc t gi tr ny rt be, nn in tr 34 ra s v cng ln v c th b qua. Mch tng ng n gian hoa cua BJT (toan hc) i2(io) i1(ii) v1(vi) h11(hi) v2(vo) h21i1 (hf) Mch tng ng n gian hoa cua BJT mc kiu CE iC(io) iB(ii)

B C C B vBE(vi) hfEiB hiE vCE(vo) E E 35 Mch tng ng cua BJT mc kiu CE (vt ly) B

iB iB rB B riE rE iE iCEO iC C rCE

E - rE: in tr ca vng ngheo emitter i vi tin hiu xoay chiu. nhit thng: rE 26 [mV ] 26 [mV ] I E [mA ] I C [mA ] - rB: in tr bn thn ca min base i vi dng IB. i vi cc BJT cng sut nh rB = (100300). - rC: in tr ca vng ngheo collector, c gi tr rt ln (hng M). 36 Mch tng ng cua BJT mc kiu CE (vt ly) iC C B iB ICEO

iB rCE riE riE= rB+(+1)rE E Mch tng ng cua BJT mc kiu CE (vt ly) n gian hn iC iB B C hfEiB=iB riE V >>1 v rB << rE: riE rE E

37 IV. PHN TCH MCH KHUCH I TN HIU NH 1. Mch khuch i mc E chung RB1 RC C2 C1 RL RS RB2 RE CE vS 38 Cac thng s cua mch khuch i i vi tin

hiu xoay chiu: - in tr vo. - in tr ra. - li dng. - li p. 39 VCC RB1 C1 RC C2 RL RS RB2 vS RE

CE S tng ng v mt xoay chiu RS vS RB1 RB2 hie rie rE hfe hfeiB RC RL 40 in tr vo iS RS vS

iB RB1 RB2 hie rie rE hfe hfeiB RC iL RL RiE t: RB = RB1 // RB2 ; rL = RC // RL RiE = RB // hiE Nu RB >> hiE th RiE = hiE - Nu dng mch tng ng vt ly:

RiE = RB // rE rE = 0.026/IE ( nhit phng) 41 - in tr ra: iS RS iB RB1 RB2 hie rie rE vS iL hfe hfeiB RC RL

RoE RoE = RC 42 - li dng tng: AiE = iL/iS iS RS vS Vin iB RB1 RB2 VL i L R L h fE i B rL Vin i S R iE i B h iE hie rie rE

hfe hfeiB RC iL RL VL rL i L h fE i B RL h iE i S i B R iE R iE rL A i E h fE h iE R L rL rL Nu RB >> hiB: A i E h fE RL RL 43

- li p : AVE = VL/Vin RS vS iS RiE Vin RB1 RB2 iB h ie rie rE hfe hfeiB RC RoE iL RL VL

VL h fE i B rL Vin i B h iE rL rL A V E h fE h iE h iE Nhn xt: p ra ngc pha vi ap vao. 44 - li p ton phn : ATP = VL/VS iS RS iB RB1 RB2 iL hfe hfeiB RC

hie rie rE vS RL RoE RiE VL h fE i B rL VS i S ( R S R iE ) ATP R iE rL h fE h iE R S R iE Nu RB >> hiE: h iE i S i B R iE A T P h fE

rL R S h iE 45 2. Mch khuch i mc B chung RS C1 RC C2 RE vS RL VCC S tng ng RS vS

RE hiB hfBiE RC RL 46 in tr vo RS vS RE iE hiB iL hfBiE RiB

RC RL RiB = RE // hiB Nu RE >> hiB th RiB = hiB Thng thng gi tr hiB rt nh (khong vi chc ). V vy mch khuch i B chung c in tr vo rt be. 47 in tr ra RS RE iE vS hiB iL hfBiE RL

RC RoB RoB = RC 48 - li dng tng: AiB = iL/iS RS RE iE vS VL i L R L h fB i ErL Vin i S R iB i Eh iB iL hiB hfBiE

RC RL rL ; rL R C // R L i L h fB i E RL h iB i S i E R iB R iB rL A i B h fB h iB R L rL A i B h fB Nu RE >> hiB: RL Trng hp RL << RC th rL = RL: AiB = AiBmax= hfB 1 . 49

- li p : AVB = VL/Vin RS RE iE vS hiB iL hfBiE RC RL VL h fB i C rL h fB i E rL Vin i S R iB i E h iB rL A V B h fB h iB Nhn xt: p ra ng pha vi ap vao.

50 - li p ton phn : ATP = VL/VS RS RE vS iE hiB VL h fB i E rL VS i S ( R S R iB ) R iB rL A T P h fB h iB R S R iB Nu RE >> hiB: ATP iL hfBiE

RC RL h iB i S i E R iB rL h fB R S R iB 51 3. Mch khuch i mc C chung RB VCC C2 RS C1 RE vS

RL S tng ng hfeiB hie RS vS RB RE RL 52 B hfeiB C hie RS RB

E RE vS Ve li s tng ng B hie RS RB RL E RE hfeiB RL vS C

53 in tr vo RS vS hie B RB RiC RiC = RB // riC VBC = VBE + VEC E iE iB RE hfeiB RL

riC VBC ; riC iB C VBC = iB.hiE + iE.rL (rL = RE // RL) VBC = iB.hiE + (hfE + 1)iB.rL VBC riC h iE (h fE 1).rL iB RiC RB (hng trm K) 54 in tr ra RS B

RB hie E iE iB RE hfeiB vS RoC roC RoC = RE // roC VEC ; roC iE VEC = iB.hiE + iB.RS

C ; (RS = RS // RB) VEC h iE i B R'S i B h iE R'S roC iE iE hf E 1 RL (rt nh) RiC khong vi chc 55 - li dng tng: AiC = iL/iS B RS iS

hie RB E iL iE RE hfeiB RL vS VL i L R L i ErL (h fE 1)i B .rL rL i L (h fB 1)i B RL C (rL R E // R L )

riC riC Vin i S R iC i B riC i S i B i B ( R iC riC // R B ) R iC R iC AiC R iC rL (h fE 1) riC R L 56 - li p : AVC = VL/Vin B RS iS RB hie

E hfeiB iL iE RE RL vS VL (h fE 1) i B rL C Vin i B riC (h fE 1)rL (h fE 1)rL AVC riC h iE (h fE 1)rL

rL AVC 1 h iE rL h fE 1 57 Nhn xt chung: -Mch khuch i E chung c tin hiu ngo ra ngc pha vi tin hiu ngo vo. C kh nng khuch i dng v p. - Mch khuch i B chung c tng tr vo nh (vi chc ohm), tng tr ra ln (vi trm K), khng khuch i dng (Ai 1). - Mch khuch i C chung c tng tr vo ln (vi trm K), tng tr ra nh (vi chc ohm), khng khuch i p (Av 1). - C hai mch khuch i B v C chung c tin hiu ngo ra ng pha vi tin hiu ngo vo. 58

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