II. MACH KHUECH DAI CHON LOC
n lOO,uA lOO,uA
Khmi di¢n tu dung Transistor thuang duqc ling dl,lng lam khoa chuyen m<.lch, dieu khi~n trn hi¢u xung; dung de khuech d;;ti, bien ddi d1;lng xung ...
Cau hoi
1. C6 nhUng yeu t6 nao lam anh hl.ld'ng den dai thong tan 56 cua m<;lch khuech d~i? 2. Bi~n ph8:p rna n;,ng dai thOng tan 56 thap va tan 56 cao cua m<;lch khuech d<;li 18 2. Bi~n ph8:p rna n;,ng dai thOng tan 56 thap va tan 56 cao cua m<;lch khuech d<;li 18
nhL1 the nao?
3. The naD la m<;lch IQc thOng thap (h<;l thOng). thong cao (thU'Q'ng thong). thOng dai
(b~ng thong) va ch~n dai (tri~t dili, chan dai)? Cae IO?i m<;lch 19C d6 dung de
lam gl?
4. Hay cho bh~t ky hi~u va d~c di~m eua m<;lch khuech d<;Ii thu~t toano
5. Khoa di~n ttl sa d1,lng Transistor lam vi$c trong 'lung d~c tuyen nao? Khoa di~n
Chltdng 4
MACH TAO DAO 86NG . . .
I. KHAI QUAT CHUNG Vt: M~CH T~O DAO DONG HINH SIN
1. Khai quat chung
Trang linh vlfc di9ll - di¢n til, dong di¢n xoay chieu hloh sin rat quan m;mg
VI nhung d~c tfoh rieng ella no nhu: - DOng di~n hlnh sin rat d~ ph<'i.t sinh.
- Cae dong di¢n xoay chieu co troh chat luan hoan deu c6 the pM.n tich thanh m¢t chuoi cae tin hi¢u hloh sin. Dieu nay thu~n lqi cho vi~c pM.n tich, ffoh toan nha co nhieu cong cl;! toan h9c.
- DOng di~n hloh sin thuang duqc dung d~ khao sat d~c tfoh ky thu~t eua ca.c m~ch di¢n tu nhu m<!ch IQc, m~ch khUt!ch d~ ...
M1.lch dao d¢ng duqc hieu III m';lch khutch d<!i nhung khong co tfn hi~u vao rna n6 ttf t<;lO fa tin hi~u fa.
M~ch dao d¢ng t'.10 xung vu6ng nha hi¢n lUQT1g n1.lp xi ella m1.lch RC ket
hqp vai hai tr';log thai bao hoa va ngtmg dan ci1a linh ki¢n tich qrc.
M1.lch t'.10 dao dQng hloh sin dl!a tf~n hi~n tuqng c¢ng huang cua m?ch LC kel hqp YOi m?ch khuech d?i hoi tiep d~ t?O tin hi¢u.
De co tin hi¢u hlnh sin fa, m<;lch khuech d~i hoi tiep phai thoa man cae dieu
ki~n sau:
+ Xet rieng m~ch khuech d,!-i co tin hi~u y~iO Vi' tin hi~u fa V", H~ so khuech d<;li yang ha (kh6ng eo hoi tiep) eua m,!-eh khueeh d~i Ut:
v
= _ 0 =>
, v, v, v v, v, v \~ M<;ich khuech d'.li " v, tv v" M<.tch
hoi tiep duong
,,"""" "
Hinh 4.1. Sa do khoi mgch It;lO dao d(mg
+ Xet rieng m<;lch hoi tiep duang co tin hi~u vaa iii Vo , tin hi¢u fa Hl VI" H¢
s6 hoi tiep hay d¢ 19i eua m~ch hoi tiep Ii:
V
b~--L=>V ~bV
flo J . 0
Do c6 hoi tiep duang nen V, va Vr dog pha. Tin hi¢u Vi chfnh lit tcing ella
V, va VI"
Taco:
+ Xet m;;tch khuech c1~i c6 hoi tiep duong (duong rN net) baa gam d m~ch
khuech d'.li va m'.lch hoi tiep duong. Tin hi¢u ngo vito 1;\ V~, tfn hi¢u fa lit YO'
H~ s6 khuech d'.li ella taim ffi<:lch Ii:
v V
_ _ , , _ (I
Vs Vi-Vj
Suy ra: Avo
l-b.Avo
Vi-AI'"
V, - bYiA,."
Do day Iii m~ch khuech d~i dong pha nen b va Avo co tf! s6 duang, do d6 b.Avo cung c6 tT! s6 duong.
Tich s6 b.Avo chfnh la tich s6 cua hai h~ s6 khu&h d,~.i, h~ s6 khuech d~i
vong ha cua m~ch khuech d~i va h¢ s6 khuech d~i cua m~ch hoi tiep. Tich s6 b.Avu con duqc g9i HI. h¢ s6 khuech d~i vang hay d¢ lqi vang (loop gain).
Khi h¢ s6 khuech d~i vang b.Avo= 1 hay 1 - b.Avo = 0 thi:
AVF = A;" => 00
Luc do m<.tch co d¢ khuech d<.ti v6 cung l.6n va m~ch se dao d¢ng, va tlf t<;lO ra tin hi9U rna kh6ng d.n lfn hi¢u vao V,.
Tu do ta rut fa dieu ki~n cua m<;lch hI:
• H¢ s6 khuech d~i vong b.Avo = 1. (Tfch h¢ s6 khuech d~i cua m<;lch khuech di;li va h¢ s6 khuech d~i cua mi;lch hoi tiep). Dieu ki~n nay can duqc gQi la dieu ki¢n can bang ve bien d¢ dao dOng .
• Goc l¢ch (djeh) pha eua m~ch bang 0° ho~c 360°. (T6ng goe dieh pha eua m<.teh khueeh d~i va m<.teh hoi tiep phai lit hoi tiep duang). Dieu ki¢n nay can duqc gQi 13. dieu ki¢n ciln bang ve goc pha.
Neu hai dieu ki¢n tren kh6ng duqc thoa man thi m<.teh kh6ng e6 kha nang dao d¢ng.
Neu b.Avo > 1 thi m<;lch dao d¢ng tlf kich, bi~n d¢ dao d¢ng tang din. Den mQt muc nao do thI mi;leh a tn~ng thai bao hoa.
Neu b.Avo < 1 thi m<;lch dao d¢ng tlf tat dan. Den m¢t muc nao d6 thi m<.teh tra ve tr<.tng thai cat (khoa), kh6ng co tin hi¢u fa.
Neu dieu ki¢n goe pha kh6ng duQ'c thoa man thi m'.lch chi Ia mi;lch khuech d<.ti c6 hoi tiep. VI kh6ng co di¢n flp tin hi¢u va~ nen cOng kh6ng co tin hi¢u ra.
2. Cae lo~i m~eh dao d9n9 hinh sin
M'.lch t~o dao d¢ng hinh sin co rat nhieu 10~i. tuy thea tUng each phan 10<;li rna ta e6 cac 10<.ti m~ch dao dQng nhu sau:
* Neu ta philn lo~i thea phin tu tich clfe, co:
-M~ch dao d¢ng dung Transistor.
- M~ch dao dQng dung IC (m<;lch khueeh d'.li thu~t toan).
* Neu philn 10i;li thea linh ki¢n thl;! d¢ng RLC. c6:
-M~ch dao d(>ng RC.
-M~ch dao d<)ng LC.
* Neu pha.n 10i;li thea m<.tch su d1,lng bien ap. co: - Mi;leh dao d¢ng ghep bien ap.
- M<;lch dao d¢ng khong dung bien ap.
* Neu pha.n lo<;ti theo ket cau ella m<;l.ch hoi tiep, co: - M<;tch dao d¢ng 3 diem di¢n cam, 3 di~m di~n dung. - M<;tch dao d¢ng dung cau chfr T, chfr T kep.
- M<;l.ch dao d¢ng dung kh:iu hoi tiep di pha RC, CR. - M<;l.ch dao d¢ng cau vien.
* Neu phan lo~i theo linh ki¢n ket hqp khac, c6: - M<;l.ch dao d¢ng dung th<;l.ch anh.
- M<;tch dao d¢ng dung diot bien dung ...
II. Mi).CH TAO DAO DONG J DIllM
M<;tch dao d¢ng 3 di~m cling dung d6 bien doi di¢n ap m¢t chicu thanh di9n up xoay chicu hlnh sin tan so cao.
G9i Iii m~ch dao d¢ng 3 diem vllU khung dao d¢ng co 3 dilim duqc n6i voi 3 qrc cila Transistor (con d6i v6i IC khue'ch d~i thu~t toan sc duqc tdnh bay a
giao tflnh chuycn nganh khac) theo nguyen tac: Cl,Tc E pbii mac vao di6m trung gian gifra B va C.
Q,
Hlnh 4.2. Nguyen Iy mgch tr;w dao d(Jng 3 dilm
- Xet vc tfnh chat di¢n khang clla tUng dO'J,n m'J.ch thI Zcb phai cung tjnh chat v6i Z(''C Va ca 2 nguqc tfnh chat v6i Zeb'
Zc'c+ Zch+ Zch= O. Do v~y ta c6 210~i m~ch dao d¢ng 3 diem d6ta:
- M,!-ch dao d¢ng 3 ditim di¢n dung kID ~ va Zch deu mang tinh dung khang. - M<;lch dao d¢ng 3 diem di¢n cam kID 4'C va 4h deu mang tlnh chat cam khang.