- 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