r
Hinh 2.4. M(1ch khue'ch dgi vi sai co bdn
M~ch khuech d<;ti vi sai ca ban co sa do nhu hinh ve tren. Trang d6, hai
Transistor Ql va Q2 la hai Transistor cilng lo"li, d,c di¢n tra phan c,!c d6i xung
nhau c6 tri s6 gi6ng nhau.
Tin hi¢u vao duqc dua vao hai cvc BI va B2, trang do RIl13 , RIl23 la di¢n tra nh~n tin hi¢u vao cua moi Transistor.
Khi a ng6 vao (dau vao, cua vao) c6 di~n ap V; thi 1/2V; se tac d¢ng vao moi Transistor do tinh phan ap cua hai di¢n tra Rb13 , Rb23 va se c6 hai twang hqp khi c,!C BI nh~n di¢n ap duang thi c,!c B2 nh~n di¢n ap am so vai mat va nguqc l<:J.i.
Thea hinh ve, a ng6 ra (dau ra, cua ra) di¢n ap V CI giam va di¢n ap V C2
tang, di¢n tip lay ra giiia hai cvc Cia:
!:l Vo = !:l V CI- ,'J'v C2
Thong thuang Transistor duqc phan c,!c vai dieu ki¢n RB2 » rre nen d¢ lqi (h¢ s6 khuech d~) di¢n ap cua moi Transistor la:
Do ta co:
!:l V CI = A VI' I~V;I = 1/2A VI' !:lV;
to. V C1 = A V,. to. V;2 = -1/2A V2. to. V;
Suy fa:
Trang d6:
26mA r" ~ r, + (l + f3).--~
IF
2. £)~e di~m eua mi:1eh khueeh d~i vi sai
Nhu da phan tfeh b tren, khi co di~n ap tln hi9u b ng6 vao (dau vao, clra vao) thl do cau phan ap dung hai di9n trc)' RhLl , Rh23 lam cho cL!c BI co di~n ap duang va c,!C B2 co di~n ap am hay ngll'qc l~i, hie do QI dlin m"mh lam V ('I
giam va Q2 dan yeu lam V C2 lang sc cho tin hit;u ng6 ra (dau n.l, ci'ra fa) L1 V Cl va L1 V C2 ngu(.)'c dau, di9n ap ra clla mi;lch vi sai la:
L1Vo= AVc ] - L1VC2= 2;\Vc1 = 2L1VC2
Khi c6 tin hi~u nhieu pha r6i thi tin hi¢u nhicu se tac d¢ng dong thai len clfc BI va B2 vai di¢n ap dong pha (cung duang h01c cung am), nhll' v~y a ng6 ra (dau fa, ei'ra raj L1 V Cl va L1 V C2 bien thien cling huang sc tri¢t tien nhau va
L1Vo = O.
Nhu v~y, m,~ch khuech d<:ti vi sai c6 khii nang chong nhieu rfit tot. Tin hi~u
nhicu a day c6 the la tin hi¢u di9n ttt, nhi~t d¢ moi truang hay sl! hien thien di9n ap cila nguon.
3. Sa do m~ch khuech d~i vi sai thong d~ng
3.1. M~ch khuech d~i ngo V30 - ra can bang
R" r" .. Y" ... R" Q, Q, vI ~ R, <R, 1~ • 1 --=... VI G --=... V2 J
DAy la m<;ich vi sai cO him co RE d~ tang kha nang ch6ng nhieu. M'.lch dung hai nguon +Vt va -V2 doi xUng (c6 th~ kh6ng d6i xUng). Vai cach pM.n clJc nay ClJc B co the kh6ng dung du phan rip RBI' RB2 va clJC B c6 V BI := VS2:= av.
Luc do, V E se c6 di~n ap am V E "'" - 0, 7V.
Cac thong s6 ky thui~.t cua mq,ch:
- H9 so (dQ) khm~ch d~i di~n up vi sai:
A,~-j3 Rc
R/ll + rbe
- Ty s6 nen ttn hi~u dong pha r1ft Ion: - T6ng tro ng6 fa (dau fa, etta ra): fo:::: 2 Rc
Mq,ch nay thuang duqc ch9n lam m'.lch khuech di;li ng6 vaa (dau vaa, cua vaa) cua d.c tang khuech d'.li DC co ngo fa (dau fa, cua fa) doi xung.
3.2. M~ch khuech d~i ngo vao din bang va ngo ra khong can bang Mq,ch di¢n co ngo fa khong cAn bang, tin hi~u chi lAy tir clJc C I xu6ng mat nen di~n ap fa hi giam di 1/2.
R, -:':::- - - R" ,/ "V" Q2(- vv lQ,~ R, - v, ~ R, - -V, R, Rhl
Ihnh 2.6. Mqch khuech dqi vi sai ng5 vao can bang va ngo ra kh6ng con bang
Di¢n trO RE co lac dl;lng giam hi~n tuqng di~n ap tfai.
Ve phan clJc ta van co:
VBI ::: V112 ::: OV va VEl::: VE2 ::: - 0,7V
- H~ s6 (d¢) khuech d<;ti di~n ap vi sai:
I Rc
A I ~ - - jJ -::---"--
2 Rl/1+rbe
- Tong tro ng6 vao (diu vao, elra va~): ri = 2.(RB + [be)
- T6ng tro ng6 ra (d<iu ra, elra ra): rll = Rc.
M<;lch nay thuang dung lam cae tang khueeh d~i trung gian trang Ampli hay lam e;ic m~eh khueeh d~i DC.
3.3. M<;lch khueeh d.;ti ngo vao khong can bang, ngo ra can bang
R, M R" VV .. (). VV .. (). Q, Q, R, -=-V1 ~ --=-V2
Hill" 2.7. Mgch khue'ch dr;i vi sai Jlg6 vao khong CGIl bdllg,
I1go ra CGn bang
M<;lch chi co tln hi~u Vi cha vaa cY'c Bl so voi mat. Ve phan cl!c m¢t chieu ta c6:
VAl = VB2= GV. VEl = VE2= -G,7V.
Khi co tIn hi~u Vi 0 ng6 van (dau vaa, elra vaa) thl Ql khuech d~i se cha fa hai tIn hi~u 0 cl!c Cj va Ej , Ilk do Q2 duqc xem nhu Transistor khuech d~i rap theo ki6u B chung co tin hi~u vaa CI!C Ez va ra 0 CI!C C2.
Ta xet truang hqp tln hi¢u Vi c6 ban chu ky duang vaa cl!c Bl, cl!c Cj co tin hi¢u ra (Lio pha la ban chu ky am, trong khi d6 cl!c Ej c6 tin hi¢u ra dong pha Ja ban chu ky duang. 1:)6i voi Q2 c6 tIn hi¢u va~ E2 la ban chu ky duang nen
· • • i
I • clfe C2 tin hi~u fa 1a d6ng pha va c6 ban ehu ky dtIo'ng (VI m,!ch khuech diJ.i 8
chung hi m~ch khuech d<,ti dong pha).
Nhu v~y, lin hi¢u fa tren hai qrc C1 va C2 cGng la hai tin hi¢u ngucyc pha
nhau se lam cho di~n ap fa VI) tang gap d6i so vai lin hi~u V CI'
Cae th6ng s6 ky thu~t eua m':lch:
- H~ so (dt) khuech di!i di~n ap vi sai: Av= -P Re/(Rs + fhJ
- Tong tn) ng6 vao (dau vao, etTa vao): r, = 2.( RB + r he)
- Tclng tra ng6 fa (dau fa, eua ra): [0 = 2 Rc
M':lch flay co tac dl:mg deli tu tin hi~u kh6ng can bang fa tin hi~u can M.ng. 3.4. M~ch khuech d~i co ngo vao va ngo ra kh6ng dIn bang
" h RC'2 h RC'2 -v - - , R" .V" • 'V' Q,-.L Q, ViI '" R., _ _ 2 -v -.L RE
Hinh 2.S. Mgc/l khucch d(li vi sa; c6 ng6 vao va ngrJ ra k/u}lIt: call ban;.:
M9-ch chI co tfn hi~u vao Vi duqc dUa van qrc B, so v6i mal va tin hi¢u ra
lay In~n c1fc C1 so v6i mat. .
Hai Transistor QI va Q2 van co tac dl,lng io<).i tru cac tin hi~u nhieu dong pha hay khu anh huang clla nhi¢t d¢ tac dl,lng len hai Transistor.
Ve phan qrc m¢t chieu ta van eo: VBI = V B2= OV. VEl = VE2= -O,7V.
QI la Transistor khue'eh d~i dao pha, rap theo kieu Emitor chung.
~ H¢ s6 (d¢) khueeh d~i di¢n ap vi sai:
1 Rc
A, ~ - - jJ --;:--'--- 2 RH +rj".
- TOng tra ngo vao (dau vao, ei'ra vao): r, = 2.(RB + rhe )
~ TOng tro ngo fa (dau ra, etra fa): fo =. Re.
M~eh khuech d~i vi sai thuang duqe ung'dl:lng d~ ehe q.o cae m<;leh khuceh d<:Li thu~t tmin, cae Ie. ..