Mch khuch i thut ton(operational amplifier), thng c gi tt
lop-ampl mt mch khuch i "DC-coupled" (tn hiu u vo bao gm c tn hiu
BIAS) vi h s khuch i rt cao, c u vo vi sai, v thng thng c u ra n.
Trong nhng ng dng thng thng, u ra c iu khin bng mt mch hi tip m sao
cho c th xc nh li u ra, tng tr u vo v tng tr u ra.Cc mch khuch i
thut ton c nhng ng dng tri rng trong rt nhiu cc thit b in t thi nay
t cc thit b in t dn dng, cng nghip v khoa hc. Cc mch khuch i thut
ton thng dng hin nay c gi bn rt r. Cc thit k hin i c in t ha cht ch
hn trc y, v mt s thit k cho php mch in chu ng c tnh trng ngn mch u
ra m khng lm h hng.Lch sT khi mi ra i, mch khuch i thut ton c thit
k thc hin cc php tnh bng cch s dng in p nh mt gi tr tng t m phng cc
i lng khc.Do , n mi c t tn l "Mch khuch i thut ton". y l thnh phn c
bn trong ccmy tnh tng t, trong mch khuch i thut ton s thc hin cc
thut ton nh Cng, Tr, Tch phn v Vi phn vv... Tuy nhin, mch khuch i
thut ton li rt a nng, vi rt nhiu ng dng khc ngoi cc ng dng thut
ton. Cc mch khuch i thut ton thc nghim, c lp rp bng cc transistor,
cc n in t chn khng hoc nhng linh kin khuch i khc, c trnh by di dng
nhng mch linh kin ri rc hoc cc mch tch hp t ra rt tng hp vi nhng
linh kin thc s.Trong khi cc mch khuch i thut ton u tin pht trin trn
cc n in t chn khng, gi y chng thng c sn xut di dngmch tch hp(ICs),
mc d vy, nhng phin bn lp rp bng linh kin ri cng c s dng nu cn nhng
tin ch vt qu tm ca cc IC.Nhng mch khuch i thut ton tch hp u tin c
ng dng rng ri t cui thp nin 1960, l cc mch s dng transistor lng cc
A709 ca hng Fairchild, doBob Widlarthit k nm 1965; n nhanh chng b
thay th bng mch 741, mch ny c nhng tin ch tt hn, n nh cao hn v d s
dng hn. Mch A741 n nay vn cn c sn xut, v c mt khp ni trong lnh vc
in t - rt nhiu nh ch to sn xut ra cc phin bn khc ca mch ny, nhng vn
tip tc tha nhn con s ban u l "741". Nhng thit k tt hn c gii thiu,
mt s da trn transistor hiu ng trngFET(cui thp nin 1970) v
transistor hiu ng trng c cng cch inMOSFET(u thp nin 1980). Rt nhiu
nhng linh kin hin i ny c th thay th c cho cc mch s dng 741, m khng
cn thay i g, nhng li cho nhng hiu nng tt hn.Cc mch khuch i thut ton
thng c nhng thng s nm trong nhng gii hn nht nh, v c nhng v ngoi tiu
chun, cng vi ngun in cung cp tiu chun. Chng c rt nhiu ng dng trong
lnh vc in t; ch cn mt s t linh kin bn ngoi n c th thc hin c mt di
rng cc tc v x ltn hiu tng t. Rt nhiu mch khuch i thut ton tnh hp c
gi ch chng vi cent nu mua vi s lng va phi, trong khi nhng mch khuch
i tch hp hoc ri rc vi nhng thng s k thut khng tiu chun c th c gi n
c 100 dollar nu t hng s lng t.Nguyn l hot ng.u vo vi sai ca mch
khuch i gm c u vo o v u vo khng o, v mch khuch i thut ton thc t s
ch khuch i hiu s in th gia hai u vo ny. in p ny gi l in p vi sai u
vo. Trong hu ht cc trng hp, in p u ra ca mch khuch i thut ton s c
iu khin bng cch trch mt t l no ca in p ra a ngc v u vo o. Tc ng ny
c gi lhi tip m. Nu t l ny bng 0, ngha l khng c hi tip m, mch khuch
i c gi l hot ng vng h. V in p ra s bng vi in p vi sai u vo nhn vi
litng ca mch khuch i, theo cng thc sau:
Trong V+l in th ti u vo khng o, Vl in th u vo o v G gi l li vng
hca mch khuch i.K hiu.K hiu trn mch in ca mt mch khuch i thut ton
nh sau:
K hiu ca mch khuch i thut ton trn s inTrong : V+: u vo khng o V:
u vo o Vout: u ra VS+: Ngun cung cp in dng VS: Ngun cung cp in mCc
chn cp ngun (VS+andVS) c th c k hiu bng nhiu cch khc nhau. Cho d
vy, chng lun c chc nng nh c. Thng thng nhng chn ny thng c v dn v gc
tri ca s cng vi h thng cp ngun cho bn v c r rng. Mt s s ngi ta c th
gin lc li, v khng v phn cp ngun ny. V tr ca u vo o v u vo khng o c
th hon chuyn cho nhau khi cn thit. Nhng chn cp ngun thng khng c o
ngc li.Mch khuch i thut ton l tngVi mi gi tr in p u vo, mt mch
khuch i thut ton "l tng" c: li vng hv cng ln Bng thngv cng ln Tng
tr u vo v cng ln ( cho dng in u vo bng khng) in p b bng khng Tc
thay i in p v cng ln Tng tr u ra bng khng v Tp nhiu ( n) bng khngNh
th, u vo ca mch khuch i thut ton l tng khi tnh ton trong vng hi tip
c th m phng bng mt khunullator, ng ra vi mt khunoratorv kt hp c 2 (
mt mch khuch i thut ton l tng hon chnh) bng mt khunullor.Mch khuch
i thut ton thc s ch gn t c cc tng trn: bn cnh cc gi tr gii hn v tc
thay i, bng thng, in p b v nhng th tng t nh th, cc thng s ca mch
khuch i thut ton thc t s b thay i theo thi gian v c th b thay i
theo nhit , tnh trng ca cc u vo... Cc mch tch hp hin i s dng
transistor hiu ng trng (FET) hoc transistor hiu ng trng c cng cch
in Oxit kim loiMOSFETs c cc c tnh gn vi mch l tng hn cc mch s dng
transistor lng cc khi cc tn hiu ln phi x l trong iu kin nhit phng
qua mt bng thng gii hn. c bit, tng tr vo cao hn rt nhiu, tuy nhin
cc mch dng transistor lng cc thng tt hn v mt tri in p b, v n.Khi
nhng gii hn ca mt mch khuch i thut ton thc s c tm thi b qua, n c th
c xem nh mt chichp enc li. Chc nng ca mch v cc thng s c th xc nh
bng mchhi tip, v thng l hi tip m.
