7_opamp_khuyech_dai_va_ung_dung_7439

8/7/2019 7_opamp_khuyech_dai_va_ung_dung_7439

1/34

Chng 7

OP-AMP-KHUCH I VNG DNG

*********

1. Mc tiu2. Kin thc cbn cn c khi hc chng ny.3. Ti liu tham kho lin quan n chng.4. Ni dung:

7.1 Vi sai tng hp.7.2 Mch khuch i OP-AMP cn bn.7.3 Mt sng dng ca OP-AMP.

Bi tp cui chng.5. Vn nghin cu ca chng k tip.

7.1 VI SAI TNG HP:

7.1.1 Cc tng gia.7.1.2 Tng cui.7.1.3 Mt th d.

Mch vi sai trong thc t thng gm c nhiu tng (v c gi l mch vi saitng hp) vi mc ch.- Tng khuch i A

VS

- Gim khuch i tn hiu chung AC

Do tng h sl1.- To ng ra n cc thun tin cho vic s dng cng nh ch to mch

khuch i cng sut. Thng ngi ta ch to mch vi sai tng hp di dng IC gi l ICthut ton (op-amp _operational amplifier).

Ngi ta chia mt mch vi sai tng hp ra thnh 3 phn: Tng u, cc tng giav tng cui. Tng u l mch vi sai cn bn m ta kho st chng trc.

7.1.1 Cc tng gia:Cc tng gia c th l vi sai hay n cc.

a/Mc ni tip vi sai vi vi sai:

MCH IN T

Page 1 of 34Chng 7:

1/23/2000file://D:\My Documents\My eBooks\Study\Cac bai giang ve KT mach dien tu-Viet Nam\C...


2/34

l tng trvo ca tng vi sai sau c th lm mt cn bng tng trra catng vi sai trc. Tng sau khng cn dng ngun dng in.

b/ Mc vi sai ni tip vi n cc:Ngi ta thng dng tng n cc :- D s dng.- D to mch cng sut.Nhng mch n cc s lm pht sinh mt s vn mi:- Lm mt cn bng tng vi sai, nn hai in trRC ca tng vi sai i khi phi

c tr s khc nhau b tr cho s mt cn bng.- Lm tng c AVS

v AC

nn (1 c th thay i, do ch nn dng tng n

cc ni c thnh phn chung tht nh (sau hai hoc ba tng vi sai)

Page 2 of 34Chng 7:



3/34

7.1.2 Tng cui:

Phi tha mn cc iu kin:- Cho mt tng trra tht nh.- in th phn cc ti ng ra bng 0 volt khi hai ng vo 0 volt.

a/ iu kin v tng trra:c tng trra nh, ngi ta thngdng mch cc thu chung.

tnh tng trra ta dng mch tng ng hnh 7.3b; Trong RS

l tng tr

ra ca tng (n cc) ng trc.

b/ iu kin vin th phn cc:V cc tng c mc trc tip vi nhau nn in th phn cc ng ra ca tng

cui c th khng 0 volt khi ng vo 0 volt. gii quyt ngi ta dng mch di chuynin th (Level shifting network) gm c: mt ngun dng in I v mt in trR sao cho: E =

Page 3 of 34Chng 7:



4/34

RI.

7.1.3 Mt v d:

Op-amp mpc 709 ca hng Fairchild.T

1, T

2: Mch vi sai cn bn ng vo.

T3: Ngun dng in cho T

1v T

2. in th phn cc ti cc nn ca T

3c

xc nh bi cu phn th gm T6

(mc thnh diode), in tr480W v 2.4kW.

T4, T

5: khng phi l vi sai v 2 chn E ni mass. T

4c nhim vn nh in

th ti im A cho T1

v T2.

Page 4 of 34Chng 7:



5/34

T5: L tng n cc chuyn tip gia vi sai v tng cui.

T7: L mch cc thu chung u tin v T8 l mch di chuyn in th vi in tr3.4k.

T9: L mch cc thu chung cng l tng cui t c tng trra nh.

7.2 MCH KHUCH I OP-AMP CN BN:

7.2.1 Mch khuch i o.7.2.2 Mch khuch i khng o.7.2.3 OP-AMP phn cc bng ngun n.

Trong chng ny, ta kho st op-amp trng thi l tng. Sau y l cc ctnh ca mt op-amp l tng:

- li vng hA (open loop gain) bng v cc.- Bng tn rng t 0Hz n v cc.- Tng trvo bng v cc.- Tng trra bng 0.- Cc h sl bng v cc.

Page 5 of 34Chng 7:



6/34

- Khi ng vo 0 volt, ng ra lun 0 volt.ng nhin mt op-amp thc t khng tht c cc trng thi l tng nh

trn.

T cc c tnh trn ta thy:

.

- Zi nn khng c dng in chy vo op-amp t cc ng vo.

- Z0 0W nn ng ra v0 khng bnh hng khi mc ti.

- V A rt ln nn phi dng op-amp vi hi tip m. Vi hi tip m, ta c haidng mch khuch i cn bn sau:

7.2.1 Mch khuch i o: (Inverting Amplifier)Dng mch cn bn.

(7.2)

Page 6 of 34Chng 7:



7/34

Nhn xt:- Khi Z

fv Z

il in tr thun th v

0v v

is lch pha 1800 (nn c gi l

mch khuch i o v ng vo ( - ) c gi l ng vo o).- Z

fng vai tr mch hi tip m. Z

fcng ln (hi tip m cng nh) khuch

i ca mch cng ln.- Khi Z

fv Z

il in tr thun th op-amp c tnh khuch i cin th mt

chiu.

7.2.2 Mch khuch i khng o: (Non_inverting Amplifier)Dng mch cn bn.

Suy ra:

Nhn xt:- Z

f, Z

ic th c bt k dng no.

- v0

v vi cng c th c bt k dng no.

- Khi Zf, Z

il in tr thun th ng ra v

0s c cng pha vi ng vo vi (nn

mch c gi l mch khuch i khng o v ng vo ( + ) c gi l ng vo khng o).- Z

fcng ng vai tr hi tip m. tng khuch i A

V, ta c th tng Z

f

hoc gim Zi.

- Mch khuch i c tn hiu mt chiu khi Zf

v Zi

l in tr thun. Mch

cng gi nguyn tnh cht khng o v c cng cng thc vi trng hp ca tn hiu xoaychiu.

- Khi Zf=0, ta c: A

V=1 v

0=v

ihoc Z

i= ta cng c A

V=1 v v

0=v

i(hnh

7.10). Lc ny mch c gi l mch voltage follower thng c dng lm mch m(buffer) v c tng trvo ln v tng trra nh nh mch cc thu chung BJT.

Page 7 of 34Chng 7:



8/34

7.2.3 Op-amp phn cc bng ngun n:

Phn trn l cc c tnh v 2 mch khuch i cn bn c kho st khi op-ampc phn cc bng ngun i xng. Thc t, tin trong thit k mch v s dng, khi khngcn thit th op-amp c phn cc bng ngun n; Lc by gichn ni vi ngun m -V

CC

c ni mass.Hai dng mch khuch i cn bn nh sau:

Ngi ta phi phn cc mt ng vo (thng l ng vo +) in th phn cc haing vo lc ny l V

CC/2 v in th phn cc ng ra cng l V

CC/2. Hai in trR phi

c chn kh ln trnh lm gim tng trvo ca op-amp. Khi a tn hiu vo phi qua tlin lc (C

2trong mch) khng lm lch in th phn cc. Nh vy, khi phn cc bng

ngun n, op-amp mt tnh cht khuch i tn hiu mt chiu. Trong hnh a, mch khuch io, C

1l t lc in th phn cc ng vo (+). Trong hnh b, mch khuch i khng o, C

1

dng to hi tip xoay chiu cho mch v giin th phn cc ng vo (-) l VCC

/2.

khuch i ca mch vn khng i.

7.3 MT SNG DNG CA OP-AMP:

7.3.1 Mch lm ton.

7.3.2 Mch so snh.

7.3.3 Mch lc tch cc.

7.3.1Mch lm ton:

Page 8 of 34Chng 7:



9/34

y l cc mch in tc bit trong s lin h gia in th ng vo v ngra l cc phng trnh ton hc n gin.

a/ Mch cng:

Tn hiu ng ra bng tng cc tn hiu ng vo nhng ngc pha.Ta ch l vi l mt in thbt k c th l mt chiu hoc xoay chiu.

b/ Mch tr:Ta c 2 cch to mch tr.

* Trbng phng php i du: tr mt s, ta cng vi si ca s.

v2u tin c lm o ri cng vi v1. Do theo mch ta c:

Nh vy tn hiu ng ra l hiu ca 2 tn hiu ng vo nhng i du.

Page 9 of 34Chng 7:



10/34

* Trbng mch vi sai:Dng cbn

Thay tr s ca vm

vo biu thc trn ta tm c:

c/ Mch tch phn:Dng mchDng in ng vo:

* Hai vn thc t:- iu kin ban u hay hng s tch phn:

Page 10 of 34Chng 7:



11/34

Dng mch cn bn

s thp. Nh vy khi c Rf, mch ch c tnh tch phn khi tn s ca tn hiu f tha:

, Rf

khng c qu ln v s hI tip m s yu.

d/ Mch vi phn:Dng mch

Vn thc t: gim tp m.Mch n gin nh trn t c dng trong thc t v c c tnh khuch i tp

m tn s cao, y l do li ca ton mchtng theo tn s. khc phc mt phn no,ngi ta mc thm mt in trni tip vi t C ng vo nh hnh 7.19.




12/34

7.3.2 Mch so snh:

a/ in th ng ra bo ha:Ta xem mch hnh 7.20

Trong A l li vng hca op-amp. V A rt ln nn theo cng thc trnv

0rt ln.

Khi Ed

nh, v0c xc nh. Khi E

dvt qu mt tr s no th v

0t n tr

s bo ha v c gi l VSat

.. Tr s ca Ed ty thuc vo mi op-amp v c tr s vo khong

vi chc mV. - Khi Ed

m, mch o pha nn v0=-V

Sat

- Khi Ed

dng, tc v1>v

2th v0=+V

Sat.

in th ng ra bo ha thng nh hn in th ngun t 1 volt n 2 volt. l |+V

Sat| c th khc |-V

Sat|.

Nh vy ta thy in th Ed

ti a l:

b/ Mch so snh mc 0: (tch mc zro)* So snh mc zro khng o




13/34

* Mch so snh mc zro o:




14/34

c/Mch so snh vi 2 ng vo c in th bt k:* So snh mc dng o v khng o:

- So snh mc dng khng o:

- So snh mc dng o:

* So snh mc m o v khng o:




15/34

- So snh mc m o:

d/ Mch s snh vi hi tip dng:* Mch o:




16/34

tip dng nn v0

lun lun trng thi bo ha. Ty theo mc tn hiu vo m v0

giao hon

mt trong hai trng thi +VSat

v -VSat

.

Nu ta tng Eit t, ta nhn thy:

Khi EiV

refth v

0=-V

Sat

Tr s ca Ei=V

ref=b.(+V

Sat)lm cho mch bt u i trng thi c gi l im n

trn (upper trigger point) hay im thm trn (upper threshold point).V

UTP=b.(+V

Sat) (7.12)

By gi nu ta gim Ei t t, ch l lc ny v0=-VSat v Vref=(-VSat), ta thy khiE

i


17/34

* Mch khng o:

Dng mch

- By ginu ta gim Ei

(v0ang l +V

Sat), khi V

Abt u nh hn V

ref=0v th

v0i trng thi v bng -V

Sat. Tr s ca E

ilc ny gi l im ny di V

LTP.

Tnh VUTP

v VLTP




18/34

- Khi gim Eit tr s dng dn xung, lc ny v

0=+V

Satnn:

e/ Mch so snh trong trng hp 2 ng vo c in th bt k vi hi tipdng:

*Dng mch khng o:Dng mch




19/34

Khi VA

=Vref

th mch i trng thi (v0i thnh +V

Sat), tr s ca E

ilc ny gi l

im ny trn VUTP

. T (7.17) ta tm c:

bng Vref th mch si trng thi, tr s ca Ei lc ny gi l im ny diV

LTP. Tng t nh trn ta tm c:

nu |+Vsat

|=|-VSat

|

* Dng mch o:Dng mch cn bn nh hnh 7.38




20/34

, cng l tr s ca V

A, gi l im ny trn V

UTP.

Nu ta gim Eit t, n khi E

i=V

Amch si trng thi (v

0= -V

Sat) v E

i=V

A

lc c tr s l VLTP

(im ny di).

7.3.3 Mch lc tch cc: (Active filter)C 4 loi mch chnh:- Mch lc h thng.- Mch lc thng thng.- Mch lc di thng.- Mch lc loi tr(di trit).

a/ Mch lc h thng(Low pass Filter-LPF)




21/34

* Mch lc h thng cn bn:Dng mch

Nu ta chn R2=R

1th |A

V0|=1

p tuyn tn s dc -20dB/dec v khi tn s tng ln 10 ln th khuch igim i 10 ln tc -20dB. Ngi ta hay dng mch voltage follower lm mch lc nh hnh7.41. y l mch khuch i khng o, nhng do khng c in trni mass ng vo (-)nn li bng +1.




22/34

Ngi ta thng chn R

f=R gim dng offset.

* Mch lc h thng -40dB/dec:Trong nhiu ng dng, ta cn phi gim nhanh li ca mch khi tn s vt

qu tn s ct, c ngha l dc ca bng tn phi ln hn na. l mc ch ca cc mchlc bc cao.

Dng mch

Nu chn C2=2C

1, ta c:




23/34

mch ny khuch i s gim i 40dB khi tn s tng ln 10 ln ( li gim i 100

ln khi tn s tng ln 10 ln).

* Mch lc h thng -60dB/dec:t c dc hn na-gn vi l tng-ngi ta dng mch lc -20dB/dec

mc ni tip vi mch lc -40dB/dec c dc -60dB/dec ( li gim i 60dB khi tn stng ln 10 ln-gc pha ti tn s ct l -1350).

Dng mch cn bn nh hnh 7.44




24/34




25/34

b/ Mch lc thng thng (high-pass filter)y l mt mch m li ca mch rt nh tn s thp cho n mt tn s

no (gi l tn s ct) th tn hiu mi qua c ht. Nh vy tc dng ca mch lc thngthng ngc vi mch lc h thng.

* Mch lc thng thng 20dB/dec:Dng mch nh hnh 7.46

y l mch voltage follower nn AV=1. Do in th ng ra v0 bng vi in th2 u in trR nn:




26/34

Khi tn s cao, tng trca tin khng ng k nn A

V0=v

0/v

i=1. Khi tn s

gim dn, n lc no li bt u gim. Tn s m ti li gim cn 0.707 AV0

gi l

tn s ct. Lc ta c:

Ta cng c th dng mch nh hnh 7.48




27/34

* Mch lc thng thng 40dB/dec:Dng mch

Do l mch voltage follower nn in th 2u R1

chnh l v0. Ta c:




28/34

* Mch lc thng thng 60dB/decNgi ta dng 2 mch 40dB/dec v 20dB/dec ni tip nhau t c dc

60dB/dec.




29/34

Chn C1=C2=C3=C;

Ti tn s ct:

c/ Mch lc di thng: (band pass filter)




30/34

y l mt mch m ng ra ch c mt di tn gii hn no trong ton bdi tn ca tn hiu a vo ng vo.

Vi mch ny in th ng ra v0max

t n tr s ti a mt tn s no gi

l tn s cng hng wr. Khi tn s khc vi tn s cng hng, khuch i gim dn. Tn s

thp hn wrlm li gim i cn 0.707v0max gi l tn s ngt thp wL v tn s cao hn wrlm li gim cn 0.707v

0maxgi l tn s ngt cao wh.

Bng thng c nh ngha:B=wH - wL

Khi B0.1wrc gi l mch lc di thng bng tn rng.

* Mch lc di thng bng tn hpDng mch




31/34

Ti tn s cng hng wr:

T phng trnh (a) ta tm c:




32/34

* Mch lc di thng bng tn rngThng thng c mt mch di thng bng tn rng, ngi ta dng hai

mch lc h thng v thng thng mc ni tip nhau nhng phi tha mn iu kin tn s ctw2 ca mch lc h thng phi ln hn tn s ct w1 ca mch lc thng thng.




33/34

Ta tm c 2 tn s ct l:

Phi chn R1, R

2, C

1, C

2sao cho w1 < w2.

d/Mch lc loi tr: (di trit-Notch Filter)y l mch dng lc b mt di tn s no trong ton b di tn. Mch

thng c dng lc b cc nhiu do mt b phn no trong mch to ra th d nh tns 50Hz, 60Hz hay 400Hz ca mt.

C rt nhiu dng mch lc di trit, thng dng nht l mc 2 mch h thng vthng thng song song vi nhau hoc c th dng mch nh hnh 7.58.




34/34

Ging vin: Trng Vn Tm
