I, R2=LR 4, Nhu v~y mQt cau can bang la cau co:
d) IS), mall I'd gill: (sampled&hel
tin hi~u wang ttf thanh philn nha, ket qua uua fa m9t ioq.t cac xung h~p, hlnh 2.20 e. 139 trich va gift mau 0), hlnh
2.21, duqc sir dl;lng M giil tUng gia tfj duqc lay mau eho den khi xung tiep thea xuAt hi~n, hinh 20 d. B9 (1) t6ch va giil mau tin hi~u wang ttf, vi~c ehuyen doi thanh tin hi~u so duqc thl,lc hi~n I~i (2)- b9 ehuy~n doi tllang t\\"- s6, hlnh 2. 21.
Moi quan h~ giila vi~c lay mall, diiu vao VA va dau ra ella mQt bQ ehuyen ddi tuang t\\" -.so duqe minh hO<;l t<).i hlnh 2.22 eho m9t duu fa 3 bit. Nhu da biet,
s6 nhj ph{m; 0 va I dU'<)'c g9i 13. bits, 111¢t nh6m cac bits gQi Iii 1/(, vi trf cua d.c bit" trong m()1 ttl co )' nghla: bit cao nhat (nam C\!C trai tlI) va "bit th,tp nha't (nAm C\!C phai cua tiI) vi til,!: 2 ,... , -, " 2' 2' 2'
bit cao nhit bit thap nhat. Chicu dui cua mQt
tiI (\vord ienght) quyet d~nh d9 ph[m dai cua cau tll, tuc SlJ thay d6i nh6 nh{lt trong V \ se dan den SlI thay doi lrong tin hi~u ra ~o. S\! thay d6i nh6 nhat trong dau ra so. la m¢t bit 6
vi trl thap nhrlt trang til. Do vay v6i mOt chieu dai tli co /I bit, tOliO thang dau vao tlIdng til
VI'~ se dl1Q"c chia thanh 2n
mau, nhU' v~y st! thay d6i It nha·t d dAu vao c6 tht nh~n d,!-ng dU'Q"c, hie d¢ phan dili cua hi)
chuyen deli dlIQc xac djnh 1£1 Vf.J2". Vi d~,
Vao, T rich &giCl mau Chuyen doi R;;
Tin hieu ttlang 11,1 (1) ~ (2) Tin hieu so
· 0 . 101 \-, ,~. i ,~. i :.;::1001 ~.'lJ I ~ ! , I OOO''---'---~- ~S o 118 ZiS 318 418 ~ 618 j,,<! i\.8
Till bitu lI.!Oug t\lrn phfl.u s6 cUa gili ![~ FS
lJinh 2.22 . Quan h¢ MIl VOO-1"I1 ('da m(if b(! rIll/yin ddi tur:mg /1/ -sri'
mOt b¢ chuy6n doi wong tl! -s6 c6 chieu dai tiI 1£1 10 bits va tin hi~u wong tl! a toim thang la lOY, khi d6 d¢ phan d5.i se 1A 10/2111 ~ 9,8mV.
Thu(\t ngli l}Ufi gial1 cf1l('yi'n (1tl,. (conversion time) dUlJc si'r dl,!og d<i xal.: dinh thdi gian de b¢ chuytn doi sinh dil m¢t tli (word) khi du<;,c cap mQt dilu vao- tuang t\!. Thuemg thai gian chuye'n doi til khoiing ,"",s.
Nhfrng nguyen If tr~n duqc si'r d~ng trong bQ chuy~n d6i luang t\!- so.
B(i chuyin tIdi /liang tl{-S(/:
Ball vao la tin hi?u tlJong tl! va Mu ra 13. mQt ttl nh~ phan (binary word). B9 chuye'n doi tlJ'dng tt!- s6 co m9t s6 d<}-ng, d~ng thuang dl1Q"c si'r dl:lOg nhai la loq,i xfip xi kc tiep (successive approximation). I-Hnh 2.21 the' hi9n lUll d6 cua m¢t bQ
ehuycn d6i tuang tl! -so xap xi k6 tiep. MOt di9n ap duqe sinh boi dong h6 khi rh5.t r:.t day tufln tl! cae xung. Cae xung nay dU<;Ie oem thea kieu s6 nhj phan va III nl1i phall t~o !len dUQ"c chuyen thanh lllQI di¢n ap tUOOg tl! bai hQ chuyen d(~i
Tin hIi~u vaG n.rcrng III I DAe I [" I . I • ~~ Bo sQsanh _ ~.=:-~I Eo Mm W Cong I __ I . i i i ! D6ng he ,
Hinh 2.23: Br) chl/y/n d6"i Il((lI1g fl/- -s6',heo xiip xi hell {(It
L S B - - - - · Msa
Bitcaol1o.nt Bittb.~[)ul:!at
Hinh 2.24: B(i thl/yin d6'/ sf;'-f/t(fng 11/
M Ihtfl/g fhallg R-2R
sang s6 (DAC). Di¢n rip nay tang thea h<)c va dUQ"C so sanh vai tin hi¢u Woog tl! dau vao til cam bien. Khi di¢n up sinh bai dong ha (clock) VlIqt qua di~n rip Miu vao wem.g tl!, xung tlr dong h6 bi dirng, kh6ng dUQ"e dem tiep do c6ng (gate) dong. Dau ra khoi bi) dem (counter) t;:ti thai diem do bieu dien tin hi¢u so eua di¢n ap tUoog tl!. Thay vi sl! so sanh co the thllC hi¢n bai khoi dau de'm tQ,i I bit thap nhat, rai tiep tye bit thea bit thl phuoog phap xap xi ke tiep eha phep thl!e hi¢n nhanh hon. B¢ chuyen d6i Wem.g tl,l' so xap xi ke tiep tuyen chQn bit cao nhat, nhlffig nha hem. gia tr~ tuem.g tI!, roi b6 sung cae bft nh6 hoo ke tiep, nhlffig toan bi) kh6ng dUQ"c VUqI: qua gia tr~ tuem.g tl!. Vi moi mOt bit cua tiI du\iC thir thea tuan tl!, nen m0t tiI co n hit can n b~c thl!c hi¢n so sanh. Neu dong h6 co t,1.11 so fthl thai gian chuyen doi siS la niL
B(} chuye'n ddi S(j:lll(fllg t~(:
Dau vao hi) chuycn d6i Iii. mQt tli (word), dau ra Iii. tin hi¢u tuang tl!, ia t6ng
cua d.e bits klu)llg zero trong lit. M9t trong nhlrng d~ng ehuyen doi so- tuang tl,l' thuang dUQ"c sir d1,lng la h¢ thong thang R-2R (hlnh 2.24). Di¢n ap dau ra duqc sinh hoi vung d6ng/ngat cua thang den di¢n ap chuAn (RRd) ho~e ov tuy thea dau vao - tin hi¢u sola bit 1 ho~c bit O.
B(i (16'11 k('nh (multiplexer): trong
thJ.!c te thuang can thiet thJ.!c hi~n cac phep do M lay mau tir m¢t so cac vi trl khac nhau ho~c thl,lc hi~n 1l19t luqng cac phep do khac nhau. Thay VI sii dl,lng tirng bQ vi xU" tf ricng cho moi phep do, co tht siI dt;lng m¢t b9 don kenh. E9 don kenh (hlnh 2.25), thJ.!C chat lA m¢t thiet bi dao ll1~ch, cho phep moi m9t tin hi¢u dau vao c6 th~ hin lUQ1 duqc lay mau.
Ph~n nh6& , Chuyen di'i"i luang tu·so • Tuant\Icac lin hil~u so
Ilinh 2.25: Chuye'll ddi II((ing II/-Mi" sIr d'.lIlg h¢ don kenh
Bq d¢m (huffer) thuang dugc Slr dVng khi cae tin hi~u den b¢ xu Ii qua nhanh, ho~c khi do b9 xu H dang b~n thlFc hi~n 1l19t c6ng vi¢c khac nen khong th~ chap nh~n cac t10 hi~u t'!-i thoi gian chung tm. M~t khae dau ra'khoi b9 vi Xlr
11 d~ den ed cau chap hanh ho~e cac thiet bi khac co thi! la qua cMm, do v~y can co b¢ nha ngoai gQi la b9 d¢m ae luu tril
t~m thOi tin hi¢u.
Doi vai phan d¢:m dau vao, dii li¢u duqc truy6n khoi n6 voi toe d9 quyet dinh bbi b9 vi xu If. V 6i phan d¢1l1 dau ra, toc dQ truyeo duge quyet dlnh boi thiet bi dugc cap. B¢ nha d~m dl~n day ho~c trong ding dt bu cho chenh l~ch giila toe d¢ vao b¢ d¢m va toc d9 ra yeu duo Kha naog eua b¢ d¢m phI.). thuQe vao dung tich b¢ nha va chenh l~ch trong toe d¢ truycn dau vao va dau ra.
2.3.2.8. Dietl bien (modulation)
Khi truyen cae tin hi~u DC mvc thap tll cae sensor va dUde xii If b6'i b9 khuech
d,!-i thu~t tmin eo the: xA:y ra hi¢n tLIqng Hinh 2.26: Di/u bie'll bien di} xllnR
troi (drift) tin hi¢u. Van dC nay c6 the tdnh duqc neu thl).'c hi¢n dieu bien, tue truycn tin hi¢u liin lUQ1 (chu kh6ng truyen trl).'e tiep), Caeh truyeo nay con giup
tranh dl1qc giao thoa tin hi¢u. Hinh 2.26 tht hi~n sl! dit'!u bien bien d¢ xung dong
DC va hinh 2.27a) the hi¢n dieu bien bien d¢, hlnh 2.27b) the hi¢n dieu bien tan so eua m¢t dong AC. Sau kill dl1qc tfUyen, cac lin hi~u da dieu bien dl1qc giiH bien de tra ve tr<,lng thai tin hi¢u ban dau.
a) Bien dq
2.3.3. He thong hi~n thi