🔙 Quay lại trang tải sách pdf ebook Giáo trình kĩ thuật xung - số Ebooks Nhóm Zalo TS. Ll/ONG NGOC HAI GIAO TDiNtl Kl THUfiT XUNG - SO (Sack dung cho cac truong dao tao he Trung hoc chuyen nghiep) (Tai ban Ian thii nhat) 0*1 HQC THAI NGUYEN TRUNG TAM HQC LIEU NHA XUAT BAN GIAO DUC Loi gioi thieu Nam 2002, Vu Giao due Chuyen nghiep - Bo Giao due va Dao tao da phoi hap vdi Nha xuat ban Giao due xuat ban 21 giao trinh phue vu eho dao tao he THCN. Cac giao trinh tren da ditac nhieu tritdng sit dung do hoan nghenh. Be tiep tuc bo sung nguon giao trinh dang eon thieu, Vu Giao due Chuyen nghiep phoi hap eiing Nha xuat ban Giao due tiep tuc bien soan mot so'giao trinh, saeh tham khao phue vu eho dao tao d cac nganh : Bien -Bien tic, Tin hoc, Khai thac ca khi. NhSng giao trinh nay tritdc khi bien soan, Vu Giao due Chuyen nghiep da giei di citdng vi tren 20 tritbng va to chiic hoi thao, lay y kien dong gop ve noi dung d i cMng cac giao trinh noi tren. Tren ca sa nghien ci'(u y kien dong gop cua cac trU'ang, nhom tac gia da dieu chinh noi dung cac giao trinh cho phu hap vdi yeu cdu thite tiin han. Vdi kinh nghiem giang day, kien thiic tich luy qua nhieu nam, cac tac gia da ed ging de nhSng noi dung duac trinh bay la nhdng kien thite ca ban nhat nhUng van cap nhat ditac vdi nhitng tien bo cua khoa hoc ky thuat, vdi thite te san xuat. Noi dung cua giao trinh eon tao sit lien thong tit Day nghi len THCN. Cac giao trinh ditac bien soan theo hudng mb, kien thite rang va co gang chi ra tinh ling dung cua noi dung duac trinh bay. Tren ca sd do tao dieu kien de cac tritbng sit dung mot each phu hap vdi dieu kien ca sd vat chat phue vu thite hanh, thite tap va dac diem cua cac nganh, chuyen nganh dao tao. De viec doi mdi phitang phap day va hoc theo chi dao cua Bo Giao due va Dao tao nham ndng cao chat luang day va hoc, cac tritdng can trang bi d i sack cho thit vien va tao dieu kien de giao vien va hoc sinh co di. sack theo nganh dao tao. Nhitng giao trinh nay cung la tai lieu tham khao tot cho hoe sinh da tot nghiep can dao tao lai, nhan vien ky thuat dang trite tiep san xuat. Cac giao trinh da xuat ban khong the trdnh khoi nhSng sai sot. Rat mong cac thay, co giao, ban doc gop y de Ian xuat ban sau ditac tot han. Moi gop y xin giti ve : Cong ty Cophdn saeh Dai hoc - Day nghi 25 Han Thuyen - Ha Noi. VU GIAO DUC CHUYfiN NGHI$P - NXB GIAO DUC 3 J\AS c l a w Giao trinh K f THUAT XUNG - SO duoc bien soan vdi m uc dich phue vu viec hoc tap va giang day d cac trudng Trung hoc chuyen nghiep va Cao d in g kT thuat. Cuon saeh nay de cap chu yeu la n oi dung xung - so thuc hanh, tuy nhien no v§n bao dam m ot kien thUc ca ban va du rong cua kT thuat xung - so, nhung phan nguyen ti thanh tap va cau true ben trong cua cac m ach xung so chifc nang hau n h u bi loa i bo hoan toan. Vdi m di m ach chifc nang, tac gia c h i giup ban doc tra Idi ba cau h o i: No la gi, so do khoi ra sao ? Vai vi mach cua no va cach ghep noi m o rong nhu the nao ? No hay duoc dung lam gi ? Vdi cach dat van de n h tf tren, cuon saeh khong qua 250 trang nay khong the la tai lieu tham khao m d rong kien there ve kT thuat xung - so cho ban doc. Vay no giup ban doc dieu gi ? • Vdi ban doc la hoc sinh THCN hay Cao dang, cuon saeh se trang bi cho ban doc m ot kien thCfc tinh gian, thuc dung va khong the it hdn ve ITnh vac kT thuat xung - so. • Vdi ban doc la giang vien m on hoc, cuon saeh thi/c chat chi la nhCfng bai giang eCia tac gia da day cho sinh vien Cao d in g cac nganh Dien, trudng D ai hoc Bach khoa Ha Noi trong nhieu nam. Tac gia ehinh li va tinh gian lai, de m ong co the dong gop vdi dong nghiep khi soan bai giang mon hoc. N oi dung cua giao trinh dude bien soan bao gom : 10 chudng, 7 phu lue va m ot so bai thuc hanh chon loc vdi thdi lUdng 45 - 60 tiet. Trong qua trinh sCf dung, tuy theo yeu cau cu the co the dieu chinh so tiet trong m di chwong. Cac ban doc chcfa co m ot chut kien thCfc gi ve logic thi sau khi doc chudng 1, hay doc cac phu luc 1 + 3 de co day du kien thirc co ban. G idi thieu cuon saeh nay, tac gia chi' m uon co dong gop nho vao cach hoc va day m on hoc cho hoc sinh THCN va Cao dang. R at mong nhan duoc nhieu y kien dong gop phe binh cua ban doc. M oi gop y xin duoc gCri ve : C ong ty co phan saeh D ai hoc - D ay nghe. 25 Han Thuyen — H a Noi. t A c g i a KHAI NIEM CO BAN VE Kl THUAT XUNG - SO 1-1. CAC THONG S6 OAC TRlfNG COA TfN HI$U XUNG Cac tin hieu xung duac dung r6ng rai trong nhung llnh vuc khac nhau cua ki- thuat sfi noi riSng va cua ki thuat didn tir noi chung ; vf du trong truyin thong huu tuySn va vo tuyen, trong rada, trong do lucmg dieu khien so... Cac mach tao xung cho ra hai loai tin hieu dien : Cac xung dien ap/dong hoac nhung buorc nhay cua dien ap hay dong. Dae diem cua loai tin hieu nay la ngu6i ta chi quan tarn toi hai gia tri hoan toan phan biet nhau cua chung, goi la hai mite : Mile cao H va miic tha'p L. 1-1-1. Xung Xung la tin hieu tao nen do su thay doi miic cua dien ap hay dong trong . mot thcri khoang rat nho : Tir miic tha'p L ban diu chuyen sang njm 6 muc cao H trong m6t thcri gian ngan, hoac ngugc lai. • Hinh 1-la la m6t xung hinh thang li tucmg. Doan ab goi la day xung, doan cd la dinh xung, doan ac chuyen tir miic thap L len miic cao H goi la su&n len cua xung, doan db chuyen tiep tu H sang L goi la su&n xuong cua xung. Khoang cach gitta dinh va day goi la bien do xung UM (UM = H - L). Mot xung thuc te a cua ra mach tao xung co dang t6ng quat nhu 6 hinh 1-lb. Ta tha'y, do qua trinh qua dfl nSn dinh xung kh6ng "tron" va khong nam o mot dien ap cd dinh ; muc cao H nam trong mien dien ap giira bien do UM va 0,9UM. Sai lech Au goi la do sut dp dinh. Khoang thcri gian de’ xung tang tir 0,1UM den 0,9UM goi la thoi gian len tr (rise time); khoang thoi gian xung giam tir 0,9 UM xuong 0,1UM goi la thoi gian xuong tf (fall time) cua xung. Khoang thoi gian giua hai thoi di^m tuong ung vai gia tri 0,5 UM goi la do rong xung rx. Ngoai ra con co cac thong so phu nhu "buou" dinh b, va "buou" sau khi ket thuc xung b2. Neu 5 th o i g ian len tr va thdi g ian x u o n g tf ra t n ho so v a i d o r&ng x u n g tx, ta co x u n g v u o n g gdc. H in h 1 -lc ve cac xun g vudng go c If tu o n g cu c tin h d u a n g va cuc ti'nh am . u t c) e) HINH 1-1. Cac dang xung • N g o ai xun g vu o n g g o c iS t p h o b ien tro n g kT th u a t so, n g u d i ta co n sir du n g x u n g r a n g c u a (ram p ). H in h 1 -ld v e d a n g t6 ng q u a t m o t x u n g ra n g cua. N o g 6m h ai su o n d o c , d ac tru n g b o i th a i g ia n len d o c tr (risin g slo p e ) va thoi gian x u o n g d o c tf (fa llin g slo p e). Do'i v d i x u n g ran g c u a, n g o a i bien d o U M, n g u 6 i ta c o n q u a n tarn to i t i so d o d o c (S lo p e ra tio ) SR = tf : tf. V i d u : tr = 15m s, tf = 2 m s, ta co x u n g ra n g cu a v a i ti so d o d o c 15 : 2. N eu tr = tf th i xu n g ran g cu a go i la x u n g ta m g ia c. • Cud'i cu n g la x u n g d a n h (d in h ) co d in h ra t n h o n (h in h 1 -le ). X u n g nay thucm g d u n g d e k ic h k h a i h o a t d o n g cu a cac m ach d ie n tir. 6 1-1-2. Birdc nhay Bircrc nhay la su chuyen rtft nhanh cua difen ap hoac dong gitta hai miic H va L. N£u nhay til miic tha'p L len miic cao H thi goi la bu&c nhay duang (hinh 1- 2a) ; neu nguoc lai nhay tir H xud'ng L thi goi la budc nhay dm (hinh l-2b). Budc nhay, ddi khi con goi la tin hieu the, duoc dac trung bing bien dO nhay UM va d6 dai suan doc tf (hoac tr). Bubc nhay la tin hieu ra a nhifiu mach dien tir, vi du mach so sanh tuong tu (xem muc 2-1) hoac cac Flip-Flop (xem muc 3-1). V i Hinh 1-2. Cac bode nhay 1-2. DAY XUNG KT thuat xung khong chi tao ra nhung mach phat xung dcrn ma con co cac mach cho ra m6t day xung lien tiep (Hinh 1-3). - =3 i s xung kfch » - ‘ x K ■ r-tr* T k k k khdi Hinh 1-3. Cac day xung 7 1-2-1. D ay x u n g co th e la tu a n h o a n vdi ch u ki T , n g h la la cir sau m 6i koang thcri g ian T lai co m 6t xung lap lai hoan toan g io n g vdi x u n g tru d c no. H inh l-3 a ve ba dang day xu n g tuSn hoan th u d n g g ap sau : • D a y x u n g v u o n g g o c la d an g day xu n g thucm g g ap n h at tro n g k! thuat d ien tir. C ac th o n g sd dac tru n g cho day xung g 6m : b ien d& U M, d o r 6ng xung tx, thdi gian nghi tn, ch u ki T = tx + tn, tSn sd f = 1/T. N g o ai ra c o n h ai th 6ng sd phu dac tru n g khac la he so la p d a y y = tx/T va d o h o n g (r6n g ) Q = 1 /y = T /tx. Nd'u Q = 2, (tx = tn), th i day xun g goi la d a y x u n g v u o n g g o c d o i x u n g . • D a y x u n g r a n g c u a th u a n tu y (tf = 0 ), chu ki T . M ach p h a t d ay x u n g nay th u d n g du n g tro n g thifi't bi dao don g kf d ien tu, vdi vai tro b 6 ta o so n g quet ngang. • C uoi ciing la d a y x u n g d a n h tu a n h o a n . N o th u d n g d u n g de ki'ch khdi n hung hoat dong co ti'nh ch u k i, vl du d i6u k h ien su d o n g /m d lap lai tu in hoan cua cac khoa tran sisto r. C ac m ach p h at day x u n g tuSn ho an th u d n g la n h u n g m a c h h o at d 6ng khfing chiu su d ieu k h i^ n bdi cac x u n g kfch k h d i (kfch thi'ch) ben n g o ai va go i la cac m ach d a n g ch a y tu d o (free ru n n in g form ). 1-2-2. D ay x u n g co th e la k h o n g tu a n h o a n (h in h 1-3 b ). M ac h p h at cac xung nay la nhQng m ach h o at dOng th eo su d i6u k h iln c u a cac x u n g k fch khdi a ben n g o ai, va go i la cac m a c h d a n g k ic h k h d i (trig g e re d fo rm ). LTng vdi m6i xung ki'ch thi'ch b en n g o ai, m ach ch o ra m p t x u n g cd b ien d o va d 6 ro n g xung k h o n g thay d 6i, n g h la la d an g x u n g du a ra h o an to an la p lai gid'ng n h a u sau m6i x ung kfch thi'ch. 1-3. CAC PHAN TCTTIIY£n TfNH R-C TRONG MACH TAO XUNG C ac m ach tao xun g hay lcri d u n g q u a trin h q u a d o trSn cac p h an tir tuyen tfnh R -C de dieu k h ie n do ro n g x u n g va h e so la'p dSy ciia d ay x u n g tu a n hoan. P han tir tu y en tfnh R , C d u o c h i^ u la phSn tu co diSn trd hoac d ie n d u n g khfing thay dd i th eo gia tri d ien ap h oac g ia tri d o n g d ie n tren phSn tir. T a h ay xet vai qu a trinh qu a d o tro n g m ac h R -C . 1-3-1. Q u a tr in h q u a d o d m a c h R -C k h i co b u d c n h a y d ie n a p X et m ach R -C d h in h l-4 a . G ia sir tai th d i d iem t = 0, d ien ap u cd budc nhay d u a n g tir 0V d en U M. V ay d t > 0 ta cd : UR + UC = U M 8 Vdi uR = iR va i = Cdu^dt thi phucmg trinh c4n bang dien ap tren trd thanh : R c ^ f + uc - U M Giai phuang trinh vi phan bac 1 d tren ta duac : uc(t) = UM( I - e 't/RC) (1-D Ti'ch RC co thu nguyen thcri gian la giay (s), neu R tinh bang Q va C tfnh bang F (Fara), va goi la hdng so thoi gian rcua mach R-C (x = R.C). Tir (1-1) va phirong trinh can bang dien ap a tren ta rut ra : uR(t) = UMe 't/T (1-2) i(t) = ^ V t/T (1-3) Hinh 1-4. Qua trinh qua 36 mach R-C khi co budc nhay duang Ta tha'y dien ap trfen difen dung tang theo luSt ham mu va d t = ®, thi uc = UM. Nguac lai dien ap trfen difen tra va dong giam theo luat ham mu, khi t = co thi i = 0, uR = 0, mach dat trang thai dimg (tinh). Ve li thuyet thi qua trinh qua d6 x^y ra trong thoi gian vo ciing lan. Thuc te khi uc dat 0,9 UM hoac khi uR = 0,1 UM la coi nhu ket thuc qua trinh qua do (hinh l-4b). Thcfi gian qua d6 la : tqd = 2,3t = 2,3R.C (1-4) C) t = 3x co thfe coi uc s UM va i * 0, uR a 0. Hang so thcri gian x = RC cua mach cang lan thi thcri gian qua do cang dai (hinh l-4c). 1-3-2. Qua trinh qua do mach R-C khi ki'ch thi'ch la mot xung vuong goc Neu dat len mach R-C a hinh l-4a mot xung vuong goc (hinh 1 -5a), qua trinh qua do xay ra trong mach xem nhu la su xfe'p chong cua hai qua trinh, ling vdi hai budc nhay : Budc nhay ducrng d t = 0 va budc nhay am tai t = t, (hinh l-5b). 9 Ta co ket luan cuoi cung sau : Sir thay dd i d ien ap tren c a c phan tif R, C trong qua trinh qu a do, khi kfch thi'ch la m ot xun g vuong go c vdi do rd n g xun g tx, chiu anh hudng bdi ti so t : tx. u t u c) © t „ « x ® t„ » x t + UM U c b) 0t d> Au+U„ t 0t t Hinh 1-5. Qua trinh qua <36 mach R-C vdi kich thich la mot xung vuong goc • N eu t < tx/3 thi sir thay doi dien ap tren cac phan tu la ldn. D ien ap tren tu uc(t) tang tCt 0 den U M, sau do giam ve 0 (d u d n g 2, hinh l-5 d ). N g u o c lai, dien ap tren dien trd u R(t) g iam tir U M ve 0, sau do tai th d i d ie m tj ddi cu c tinh va tang tur - U ^ tdi 0 (d u d n g 2, h in h l-5 c ). • Ne'u x □ t x thi sir thay d d i dien ap tren cac ph&n tu la ch am . D ien ap uc(t) tang tir 0 chi tdi Au la lai giam dan ve 0 (d u o n g l, hinh l-5 d ). D ien ap uR(t) cung chi giam m ot luong Au so vdi U M la d a doi cuc ti'nh san g - (U M - Au) va tang dan vd 0 (ducfng l, h in h l-5 c ). 1-3-3. Lfng d u n g m a c h R -C tr o n g c a c m a c h ta o x u n g C ac m ach tao xung hay d u n g m ach R -C nhSm n h u n g m uc d ich sau : • Di€u ch in h do ro n g c u a xung d o n vuong goc h o ac d ie u ch in h tan so va do rdng cu a m ot day xun g v u o n g goc tu an hoan. M ach R -C c u n g co n su d u n g de tao cac xu n g rang cua. N h u n g ling dun g nay se de ca p den tro n g cac ch uong sau. • M ot irng d u n g q u an tro n g khac cua m ach R -C la de’ tao cac xu n g danh (dinh). H inh l - 6 a la m ach tao xun g din h . D ien ap ra u r ch in h la d ien ap tren dien tra R. Tir m uc 1- 3-1 va 1- 3-2 ta thaiy : K hi d a t vao m ach h in h 1-6 a m ot budc n h ay dirong h oac am thi d ien ap ra u r se la m o t x u n g d a n h d u o n g hay am . ti'nh theo ( 1- 2 ). Bien do xung danh bang bien do bu o c n h ay , day xu n g la 3t . ( t = R.C). Do do, neu d ien ap vao uv la m ot xung vuong go c co do rong xu n g ldn 10 hon ba lin hang so thoi gian i cua mach, thi b cua ra se cho hai xung danh duong va am, ung vdi sucm len va xud'ng cua xung vao uv (hinh l-6b). a> b) c) Hinh 1-6. Lfng dung R-C ibm mach tao xung dinh va mach ngin cach • Tu hinh l-5c ta tha'y, khi z » tx den miic do sut ap Au la khdng dang ke, dien ap tr£n dien trd uR hdu nhu lap lai xung dat 6 cua vao cua mach hinh l-4a, (uR a u). Loi dung hi6n tuong nay, ta co the sir dung mach hinh l-6a lam mach ngan cach ; nghla la no cho cac xung, co do rdng tx rat nho so vdi hang sd thdi gian t cua mach di qua, nhung ngan lai thanh phSn dien ap mdt chieu U0 cd d cua vao (hinh l-6c). 1-4. khoA transistor Khoa transistor la mot trong nhung phin tir co ban cua ki thuat xung - sd. Transistor dung lam khoa cd thd la transistor ludng cuc BJT hoac transistor trudng MOS. Khi su dung transistor nhu mot khoa dong/cdt, tuy theo tin hieu dieu khi£n d dau vao, transistor cd the lam viec d mdt trong hai che dd : • Che do dan bao hoa, dong qua transistor dat gia tri ldn nha't cho phep, ta noi transistor mo (hoac dan). • Che do khoa, dong qua transistor coi bang 0, ta noi transistor khoa. 1-4-1. Khoa transistor BJT Hinh 1 -7a la so dd thong dung cua khoa transistor ludng cuc, vdi dien ap dieu khien d d£u vao uv. So dd dung transistor Si loai n-p-n cd dong cuc gop a che do khoa rat nho : ’c - ^co K 11 trong do Ico la don g n g u ac cu a m ien tiep g iap g o c -p h a t ; D ien a p k h o a : la du Ion. u be = U K * ° - 6 + ° - 7V Tai thcri diem tQ, khi uv a m iic cao H sao ch o d ien ap u ^ Ion hern d ien ap khoa U K thi tra n sisto r ch u y en tit che' d o k h o a vcri ic a 0 san g che' do d in bao hoi (hinh l-7 b ). +U cc ’ f --------- V 0,9IC ---------l o. 1 ic UCc 0 n r:............- f o,9U ____ l/ l. o,iucccc Hi-’- ■ - c) b) Hinh 1-7. Mo ta si/ lam viec cuia khoa transistor BJT. O che do bao hoa, hai m ien tiep g ia p cu a tra n sisto r d eu d u o c th ien a p thu£n va dien ap tren cac cuc : u be * 0,7 V , u be * 0 ,5 V , u ce a 0,1 V D ong cuc gop ic d at g ia tri g io i han : i _ t _ ^ c c u ce _ U c c c c R c R c(1 -5 ) D ong circ goc ib c u n g d a t ta i g ia tri ting v a i d iem g id i han cu a bao h o a : i T _ . U cc *b - ! b - “5- ~ B B .R , 12 ( 1- 6 ) trong do B la he s6 khue'ch dai dong tinh cua transistor. De bao dam transistor lam viec a che dd bao hoa sau, khi tinh toan ta chon dong cuc gtfc ib a che' do bao hoa ldn hon gia tri IB tfnh theo (1-6): U„, ■b - KbhJB - Kbh B.R„(1-7) trong do Kbh la he so bao hoa, thucmg chon Kbh = 2 -h 3. Tir day ta tinh duoc miic cao H cua dien ap dieu khien uv, cin thiet de duy tri transistor a che' do bao hoa : uv = ube + ibRB = 0,7V + KbhIBRB = H (1-8) Dien ap ra chinh la dien ap cuc gop uc. Khi din bao hoa thi uc = uce = 0,1V a 0 Tir hinh l-7b ta thay, can co mot thcri gian qua do tm de transistor chuyen tir trang thai khoa sang trang thai mo (din bao hoa). Tai thoi diem tj, khi uv 6 miic tha'p L sao cho ube < UK a 0,6, transistor se chuyen sang trang thai khoa vcri: “ ^co a 0 va uc — Ucc — icRc a +UCC De chuyen tir trang thai mo sang trang thai khoa cung can thcri gian qua do tk. Thcri gian nay la cin thie't de’ triet tieu cac hat mang dien trong mien tiep giap p-n cua transistor va de tu ki sinh Cce duoc nap diy. Thcri gian khoa tk ldn hern * 7 * 1 -9 thoi gian mo tm va chung thucmg d trong khoang tir vai chuc ns (Ins = 10 s) den duoi 100ns. V ,+U , +U llRo = +u u„= L ur=0 uv= H Kh6a K md Kh6a K dong a) b) Hinh 1-8. M6 hinh hoat ddng cua khoa transistor Tom lai, ta co the mo hinh hoa su hoat dong cua khoa BJT 6 hinh l-8a nhu hoat dong cua khoa co khi 6 hinh l-8b. No co tac dung nhu mot khoa chuyen mach phu tai. Khi dien ap dieu khien uv a muc thap L, khoa K md (tuong ung 13 vdi trang thai khoa cua tra n sisto r) va d ien ap ra u r d a t le n tai b an g + U . K hi Uy 6 mire cao H, k h o a K do n g (tu o n g ting vdi tran g th ai d in bao h o a cu a tran sisto r), d at len tai la dien ap ur = 0 . 1-4-2. T a n g to e d o c h u y e n tr a n g th a i c u a k h o a tr a n s is to r B J T . Co hai each hay dung de tan g toe d d c h u y en tran g thai cu a k h o a BJT. • N oi song song vdi d ien tra cuc go c R B m d t d ie n d u n g C (h in h l-7 a ). Khi dien ap d ieu k h ien u v n h ay tflr m u c tha'p L 16n m ile cao H , luc d iu tu co i n h u lam n g in m ach d ien tr a R B, don g qu a tu (cu n g chi'nh la d o n g d u e g<5c ib) tan g ddt bie'n. Sau do do n g q u a tu g iam v£ 0 va don g bao ho a cu c gdc bi h an c h € bdi R B. V ay n h a co tu C m a do n g cue gdc va don g cue g o p tan g d d t bie'n ra't nhanh, n ghla la giam dirge thcri g ian qua dd tm kh i tra n sisto r c h u y e n tir tran g th ai khoa sang m a. K hi d ien ap d ieu k h ien u v n h ay tir m uc cao H x u d n g m iic th ip L , tu C se phong d ien qu a n g u 6n tin h ieu d ie u k ie n va qu a cue g d c tra n sisto r th eo chieu n g u ac vdi ch ieu d o n g cu e gd'c bao hoa. V I vay d o n g p h o n g nay co tac d u n g triet tieu n hanh don g cuc go c c u n g n h u d o n g cu e g o p , n g h la la lam g iam th a i gian qua do tk khi tra n sisto r c h u y e n tir d in bao h o a san g kh o a. • M ot n g u y en n h an q u an tro n g han chef td c dd c h u y e n tra n g th a i cu a khoa tra n sisto r BJT la th a i g ian luu g iu d ie n tfch d m ie n tie p g ia p go c - g o p ldn, khi tra n sisto r chuye’n tu b ao ho a san g k h o a. D e lo ai tru su bao hoa, ta d a t m o t diod S chottky song song vdi tiep g ia p goc - g o p (h in h l-7 c ) n h am g iu c h o cu e gop d dien the h ai tha'p h a n cuc gdc. D iod S ch o ttk y th u c c h a t la m d t ti£p g ia p m at giira kim loai va ch at ban d in loai n. D ae diem cu a lo ai d io d n ay la d o d in d ien theo ch ieu th u an cao h an loai d io d Si th d n g th u d n g va h iu n h u k h o n g co th d i gian tre khi no ch u y en tu d in sang k h o a. V i vay, khi tra n sisto r lam v iec d tran g th ai m a, toan bo don g cuc go'c h iu n h u ch ay qu a d io d S ch o ttk y . T ie p g ia p goc - gop cua tra n sisto r chi d in don g ra't n ho nen tran h d u a c b ao h o a va th d i g ia n qu a dd tk g iam kh i tra n sisto r c h u y e n tir d in b ao h o a san g k hoa. 1-5. KHUfCH THUAT TOAN LAM Vl£C 6 CH£ £>0 KHOA T rong k i th u at x u n g , n g u d i ta hay d u n g khucfch th u a t to a n lam v iec d ch £ dd k h o a de’ tao xu n g h o ac cac budc n h ay d ie n ap. 1-5-1. K h a i n ie m ve k h u e c h th u a t to a n K h u ech th u a t to an la m o t vi m ac h d e khufich d a i d ie n ap vi sai. N o cd hai dau vao d u a n g va am , kf h ieu P, N , va m o t d iu ra r. D ie n ap tre n c a c d iu vao va ra Up, u N, u r la so vdi mat". N g o ai ra khue'ch th u a t to a n c o n cd h ai d iu d£ ndi 14 vdri ngu6n cung cap ddi xting ±UCC (hinh 1 -9a). Dien ap nguon cung cap nim trong khoang ±5V + ±18V. Ngu6n cung cSip cho khuech thuat toan cung co the la ngu6n don +UCC. Trong cac so do dien, khuech thuat toan duoc bifiu dien don gian nhu 6 hinh 1 -9b va ta ngam hieu can phai co ngudn cung cap mot chieu cho no. Hinh 1-9. Ki hieu khuech thuat toan va dac tinh truyen dat cua no Dac diem cua khuech thuat toan la co he so khuech dai vi sai AD rat Ion (thudng Ad s 105 -r 106) va dien trd vao vi sai rat ldn (thucmg tir lOMfi + lOOMfl 12 13 vdi loai dung transistor BJT va tir 10 Q -s- 10 Q vdi loai dung transistor thudng), dien trd ra nho (co khoang lOOfi + 1 kQ). Dong chay vao cac dau vao vi sai P, N ra’t nho, co the coi bang 0. Cac khue'ch thuat toan dung trong xir li tin hieu co dong cho phep circ dai ddau ra khoang 5mA 4- 10mA. Cac khuech thuat toan co cong suat dong ra cd vai A (cd loai khuech thuat toan cong suat vdi cong sua't ra ldn hon 50W). Hinh 1 -9c ve dac tinh truyen dat ur(uD) cua khuech thuat toan. Dien ap uD = Up - uN goi la dien ap vi sai. Tr6n hinh ve, dudng 1 la dac tinh truyln dat li tudng (khi uD = 0 thi ur = 0), dudng 2 la dac tinh truyen dat thuc te cua khuech thuat toan (khi uD = 0 nhung ur * 0). Ta thay dac ti'nh cd hai viing lam viec : Vung tuyen tinh trng vdi |uD| rat nho va : ur = ADuD Vitng bao hod ling vdi |uD| khoang tir vai chuc |iV trd len (l|iV = 10 6V), dien ap ra ur a vung bao hoa la khdng d o i: “r = ±U bh; |u bh| = Ucc-(2 ^3 )V Vi du ± Ucc = +15V thi ±Ubh a ± 13V 15 H in h 1-10 g id i thieu so d 6 chan cua "chip" vi m ach k h u ech th u at toan HA 741. N o co hai kieu don g vo : D ong vo hinh tro n (kieu T 0 5 ) va dong vo vdi hai h an g chan song song (kieu DIPS). C ac chan 1,5 la chan noi "m at", chan 4 noi vdi ng u o n -U cc, ch an 7 ndi vdi n g u d n + U CC, chan 8 la chan bo trong. C hip 8 4 Hinh 1-10. So <36 ch£n cua jjA741 □ 8 □ 7 □ 6 □ 5 |aA 741 la khu ech th u at to an re tien , lam b an g tran sisto r BJT. "C hip" L M 3 2 4 cd 14 ch an , trong "chip" chira tdi 4 khue'ch th u a t toan. 1-5-2. K h u e c h th u a t to a n la m viec a c h e d o k h o a T ro n g k i th u at xu n g n g u d i ta thucm g su d u n g k h u ech th u a t to a n lam viec d vung bao hoa cu a d ac ti'nh tru y en dat. L uc dd , d ien ap ra u r chi cd th e nSm d hai m ile : M uc tha'p L = - U bh h o ac m ile cao H = + U bh. T a noi khue'ch th u a t toan lam viec d che' d 0), thi khoa hoan toan chuyen sang trang thai dong vdi ur = +Ubh = H. Vi vay Ud goi la ngudng dong cua khoa khue'ch thuat toan. Cung bien luan tuong tir, vdi uD ra't duong, khoa d trang thai dong. Khi uD giam tdi Um thi khoa hoan toan chuyen sang trang thai md nen Um goi la ngudng ma. Viing Au trong dac ti'nh truyen dat goi la do nhay cua khoa. Day la vung khoa khufi'ch thuat toan bat d£u va ket thuc viec chuydn trang thai dong / mo. Mdt khoa li tirorng co Au = 0. Muon giam Au ta phai chon khue'ch thuat toan co he so khuech dai vi sai AD cang ldn cang tot. • Su chuy&i qua lai giura hai trang thai dong / md cua khoa khue'ch thuat toan khdng phai xay ra tile thdi ma cin co thdi gian qua do tdm, goi la thdi gian dong / md (hinh 1-1 lc). Mdt thong sd' quan trong quye't dinh tdm la toe do xoay (Slew rate) cua khuech thuat toan. Hinh 1-1 la md ta phan tmg cua d ien ap ra ur khi cd budc nhay cua uD. Gan dung coi trong thdi gian qua do, quan he ur(t) la tuye'n ti'nh va bo qua thdi gian chet (chi ca 100ns trd lai). nghia la coi ur bat dau tang ngay tai thdi die’m cd birdc nhay cua uD. Td'c do xoay SR cua khuech thuat toan dinh nghla nhu sau : SR = H m [V/(1S] (1-9) (SR Ta tha'y, de giam thdi gian dong / md tdm cua khoa khue'ch thuat toan, ta phai chon khue'ch thuat toan cd td'c do 0,5 V/|iS, nhung loai LM318 cd SR = 7( 1-6. MACH LOGIC -MUC LOGIC 1-6-1. Bai toan logic Trong ki thuat va ddi song, ta thudng gap cac bai toan ma nhung d u kien cho trudc cung nhu tra ldi (dap ling) cua bai toan deu chi cd the nam d mot trong hai trang thai doi khang nhau : dung - sai, tot - xau, dat - re... Nhung bai toan nhu vay goi la bai toan logic. De giai cac bai toan tren can phai sir dung tdi dai sd Boole. Cac bien doc lap hay phu thudc trong dai so Boole goi chung la bien logic : Chung chi cd hai gia tri dac trung cho hai trang thai dd'i khang nhau cua mot hien tuong, ki hieu bang hai chii sd' 0 va 1. Hai gia tri 0. 1 cua bien logic cung nhu cac phep ti'nh trong dai sd' Boole deu co tinh chat hinh thite, khong mang y nghia dinh luong. 1-6-2. Mach logic Mach logic gom cac linh kien, chu yeu la cac phan tir dong / cat vdi hai trang thai dn dinh, ghep noi vdi nhau, nhim thuc hien nhitng quan he (ham) logic cho trudc. 2 . GTKTD 17 T rudc nam 1960, cac m ach logic di^u khi£n cd n g n g h iep thucm g d o cac rote c a - dien tao nen. N gay n ay , cac m ach logic chu yeu d u a c tao th an h tu cdc tran sisto r vdi vai trd n h u cac khoa do n g / cat, g o i la cac m ach lo g ic d ien tu. — Q, a) Hinh 1-12. So <36 khoi mach logic - Mire logic H in h 1 -I2 a la so d o k h o i m ach lo g ic. C ac b ien vao va ra deu la n h u n g bie'n logic. C ac bien vao A , B, C la doc la p ; cac bie'n ra Q t , Q 2 la p h u th u d c . Ne'u gia tri cac bien ra tai m o t th d i d iem ch i p hu th u d c g ia tri cac bie'n vao d th d i di^m d o , thi m ach goi la m a c h lo g ic to h o p : Q j = Q j(A , B, C ), Q 2 = Q 2(A , B, C). N eu cac bie'n ra phu th u d c ca tran g th a i ben tro n g St cu a m a ch d th d i diem xet thi m ach goi la m a c h lo g ic d a y : Q j = Q ^ A , B, C, St), Q 2 = Q 2(A , B, C, S,). 1-6-3. Mure lo g ic T ro n g cac m ach lo g ic d ien , d ien ap m an g th o n g tin ve h ai g ia tri cu a bie'n logic. D o do no ch i co the’ nam d h ai m ien g ia tri h o an to an p h an b ie t nh au , goi la hai m u c lo g ic , gdm m iic cao H va m uc tha'p L (h in h l-1 2 b ). T a tha'y : u Hmm ^ m ile cao H < U Hmax U Lmin 5 ml3:c tha'p L < U Lmax D e co dugc do On d in h n h ieu yeu cau , g id i han d u d i cua m uc cao va gidi han tren cu a m uc tha'p d c u a vao va cu a ra cua m ach lo g ic d u g c q u y d in h khac nhau. Vf du cac m ach lo g ic ho T T L , dau ra cd m iic cao nam tro n g m ie n 2 ,4V h 5V , m uc tha'p d tro n g m i£n 0 -s- 0 ,4 V ; d iu vao cd m iic cao tro n g m ie n 2 V 5V va m iic th ap nam tro n g m ien 0 -s- 0,8V . N eu tro n g m ach lo g ic ta quy udc m iic cao H dac tru n g ch o g ia tri 1 cu a bie'n logic va m uc thap L dac tru n g cho gia tri 0 cua b ien , th i m ach g o i la m a ch lo g ic IS duang. Neu quy uoc nguoc lai (H -» 0, L -* 1) thi mach goi la logic dm. Hien nay da s6' dung quy ucrc logic duong. Trong cufin saeh nay cung dung quy uoc do. Ro rang tin hieu truyen trong mach logic dien phai la cac budc nhay dien ap gitra hai miic L va H, hoac la m6t day xung vuOng goc co bien dS bang hieu cua hai miic logic. 1-7. cAc phAn tCtlogic thOng dung 1-7-1. Ba phan tur logic co ban Ba phan tit logic co ban la cac mach logic don gian nha't de thuc hien ba phep ti'nh co so tren cac bie'n logic : Phep tinh hoi (con goi la phep nhan logic), phep tinh tuyen (con goi la phep tinh cong logic) va phep ti'nh phu dinh tren m6t bie'n logic. • Phan tu VA (AND) la mach thuc hien phep ti'nh nhan logic giira cac bie'n A, B, C....o cua vao. Bie'n ra Q = A a B a C... = A.B.C... chi co gia tri 1 khi ta't ca cac bie'n vao d6u bang 1 ; Q se bang 0 khi co ft nha't mot bien vao bang 0. Hinh 1-13a la cac ki hieu thu&ng dimg cua phin tu VA trong cac so d6 logic (ve trong trucmg hop co hai d^u vao). A — A — & --- Q >1s' --- Q A — 1 B — B — a) b) c) Hinh 1-13. Ki hi$u cua cac phSn tCf logic VA. HOAC. DAO Bang chan li m6 ta quan he giua bie'n ra va cac bie'n vao cua phin tir VA 6 hinh l-13a cho trong bang 1-1. Tuong ling vdi no la bang 1-2, thd hien cac miic logic tren cac diu vao va ra cua phin tir. 19 B a n g 1-1 Bcbng 1-2 A B Q = A.B A B Q = A B 0 0 0 L L L 0 1 0 => L H L 1 0 0 H L L 1 1 1 H H H • P h a n t u H O A C (O R ) la m ach thuc h ien p h ep c6ng lo g ic g iu a cac b ien A, B, C ... d cua vao. B ien ra Q = A v B v C v . . . = A + B + C + .,. chi co gia tri 0 khi tat ca cac bifi’n vao b an g 0 ; Q se b an g 1 k h i co it n h lt mOt bien vao b an g 1 . H inh 1.13b la hai kf h ieu thucm g dun g cu a p h in tu H O A C tro n g cac so d6 logic (ve cho tru o n g h a p co hai d iu vao). C ac b an g 1-3, 1-4 d u d i d a y tucmg ling la bang chan If va ban g th e h ien cac m trc lo g ic a cu a vao / ra c u a p h in tu. A B a n g B 1-3 Q = A + B A B a n g B -4 Q = A + B 0 0 0 L L L 0 1 1 => L H H 1 0 1 H L H 1 1 1 H H H • P h a n tu D A O (N o ) la m ach thuc h ien p h ep tfnh p h u d in h tre n b ien logic A a dau vao. B ien ra Q = A co gia tri luon n guoc vcri g ia tri cu a A (b an g 1-5, 1-6) B a n g 1-5 B a n g 1-6 A Q = A A Q = A 0 1 L H 20 Hinh l-13c la cac ki hieu thucmg dting cua phin tu DAO trong cac sc do logic. 1-7-2. Cac phin tu logic van nang. Co hai phin tir logic van nang • Phin tu VA - DAO (No AND -> NAND) la mach thuc hien hai phep tinh logic lien tiep nhau : phep nhan logic tren cac bien A, B, C..., ke den la phep ti'nh phu dinh. Bifn ra Q = A.B.C... chi bang 0 khi tSt ca cac bie'n vao A, B, C,... d6u bang 1. Q se co gia tri 1 khi l't nha't co m6t bien vao bang 0. Hinh l-14a la hai ki hieu cua phin tit VA - dAo trong cac sc do logic. Ta tha'y p h in tu NAND tu cn g duong vcri m ach g6m phan tu VA n6'i tin g vci p h in t ir D A o (hinh l-15a) » 0I > Q a) b) c) d) Hinh 1-14. KI hi$u cac phcin tCrNAND, NOR, XOR, XOR • Phin tu HOAC - DAO (No OR -> NOR) la mach thuc h ien hai phep ti'nh logic lien tiep nhau : Phep c6ng logic tren cac bie'n vao A, B, C ..., ke tiep la phep phu dinh. Bie'n ra Q = A + B + C... se co gia tri 1 khi tit ca cac bien vao A, "B, C... deu bang 0 ; Q se co tri 0 khi l't nhat co mot bie'n vao bang 1. Hinh 1- 14b la hai ki hieu thong dung cua phin tu HOAC - DAO trong cac sc do logic. No tucng ducng vdi mach g6m phin tu HOAC noi ting vci phin tu DAO (hinh l-15b). 21 a) b) Hinh 1-15. Mach tuong duang cua cac p h in tit NAND. NOR • H ai p h in tu N A N D , N O R goi la cac p h in tu lo g ic van n an g vi ta co th£ dung ch u n g th ay ch o vai tro cu a ba p h in tir lo g ic c a ban. T h at v ay , tu phu luc 1 ta co : A .l = A ; A + 0 = A D o d o cac d iu vao cu a p h in tir N A N D , N O R d at n h u h in h l-1 6 a se tuong d u o n g v6i p h in tu D A O . T a lai co : A .B = A 3 = A + B nfin cac p h in tir N A N D hoac N O R n6i n h u h in h l-1 6 b se tu o n g d u o n g vdi p h in tir VA. Cud'i cu n g , v iA + B = A + B = A.B, nen cac p h in tu N A N D , N O R n6 i nhu h inh l-1 6 c se tu o n g d u o n g vdi p h in tit H O A C . A.B A — | Ny A.B B A+B S 3 > - A*B c) Hinh 1-16. Noi NAND, NOR dS dupe cac phan tCr logic co ban. 22 1-7-3. Phan tit tuong duong va khong tuong duong • Phan tu khong tuong duong hay con goi la phin tir XOR hai dau vao (viet tit tir chu EXCLUSIVE OR) la mach logic co hai diu vao va mot diu ra Q, dung de thuc hi£n phep ti'nh HOAC - LOAI TRlTtren hai bien logic A va B : Q = A ® B = A.B + B.A Hinh l-14c la hai kf hieu cua phin tir khong tuong duong trong cac so do logic. Bang 1-7 la bang chan If cua phin tir khong tuong duong. Ta thay khi A * B thi Q = 1, nghla la phin tir se bao hieu chi su khong tuong duong cua hai bien logic d cua vao. r ___ A B Q = A © B A B Q =’A © B 0 0 0 0 0 1 0 1 1 0 1 0 1 0 1 1 0 0 1 1 0 1 1 1 • Phan tur tuong duong hay con goi la phin tir XOR hai diu vao, la mach thuc hifin hai phep ti'nh lien tie'p : Phep ti'nh HOAC - LOAI TRlf tren hai bien logic A, B, tiep theo la phep ti'nh phu dinh. Bien ra Q = A ® B = A.B + A.B se bang I khi A va B tuong duong nhau (xem bang chan If 1-8). Hinh l-14d la hai kf hieu cua phin tir tuong duong trong cac so d6 logic. 1-8. CfNG DUNG CClA CAC PHAN TlJ LOGIC THONG DUNG Mot ung dung quan trong nhat cua cac phin tu logic tliong dung ke tren la dung de xay dung nhung mach thuc hien cac quan he logic phirc tap. Nhiem vu nay goi la tong hap mach Tuy nhien, ngay nay co rat nhieu mach logic chuc nang da duoc che tao sin thanh cac "chip" vi mach sd (xem muc 1-9), va viec tong hop mach tir cac phin tir logic thong dung hiu nhu khong con cin thiet dd'i vdi mot ki thuat vien. De’ thuc hien mot nhiem vu logic cu the, thucmg ngudi ta dem ghep noi cac mach logic chuc nang vdi nhau. Nhung phan tir logic thong dung a tren chi duoc dung don le lam giao dien lien he giua cac khdi logic chuc nang neu can. Do dd, viec tdng hop mach tir cac phan tir logic ca ban chi de cap d phu luc 4 de ban doc tham khao khi cin. Dudi day la vai ung dung don le phd bien : 23 1. C o n g logic. N g u d i ta con h ay dun g cac p h in tit V A , H O A C lam cu a n g o c h o th d n g tin di qua, goi la c o n g lo g ic. K hi d u p e d u n g n h u m d t c d n g , tin h ie u d a t 6 m 6t d iu vao cua cdng se dun g lam tin h ieu d i6u khi£n do n g / m d c d n g ; tin h ieu 6 d iu vao con lai la tin h ieu th o n g tin c in tru y ln qua. OK A DK=0 ___ Q=A Q=A DK:* “i y - :=o —I yQ=0 A Cdng md, thong tin A di qua C6ng (J6ng, th6ng tin A bj chan Hinh 1-17. Dieu khign dong / md cong logic G oi D K la tin hieu d o n g / m d cd n g , A la th 6ng tin lo g ic c in di q u a , ta co di£u k ien de do n g / m d n h u m o ta h in h 1-17. T ren h in h ve, v iec m& p h o n g cdng lo g ic n h u m ot k h o a co k h i K chi la h in h thiic, de d ie n d at chiic n a n g cu a c 6ng. O khoa c a k h i, th 6ng tin co th£ tru y en th eo h ai ch ieu ; n h u n g d c d n g logic, th o n g tin c h i co th e d i th e o m o t c h ie u , tir d iu vao td i d iu ra. 2. P h i n tur d a o co d ie u k h ie n (h o ic co di£u kien ) N h ieu kh i n g u d i ta hay dun g p h in tu khfing tucrng d u a n g (h o ac tuong d u a n g ) n h u m o t p h in tir D A O cd d ie u k h ie n . T h at v iy , tir b an g c h in li c u a p h in tir k h o n g tu o n g d u a n g (b an g 1-7) ta thi'y : Ne'u bie'n B lam bie'n d ie u k h ien thi khi B = 0 —> Q = A , th o n g tin A di qu a ; kh i B = 1 —» Q = A , p h in tu khong tu o n g d u a n g don g vai trd cu a p h in tir D A O . D di vd i p h in tir tucrng d u an g (bang 1 -8) th i ke't lu in ru t ra la n g u o c lai. DIO: ,X >Q=A a) Q=A OK-O 3 0 b) Hinh 1-18. Phan tCrDAO cd dieu khien H in h 1-18 m o ta h o at d o n g cu a cac p h an tir tu o n g d u a n g va k h o n g tucrng d u a n g n h u m o t p h an tu D A O cd d ieu k h ie n . C h u n g ch i trd th a n h p h an tir D A O khi tin h ieu d ieu khidn D K = 1 (h o ac D K = 0 d d i vdi p h in tu tu o n g d u o n g 24 hinh l-18b).Vdi tin hieu didu khi^n nguoc lai thi cac phin tu nay tro thanh mot cua ngo ma, cho thflng tin A di qua (hinh l-18a). 3. Phan tur HOAC - LOAI TRiT nhieu dau vao Nguoi ta con hay dung cac phin tir khOng tuong duong de thanh lap mach XOR thuc hien phep tinh HOAC - LOAI TRlT tren nhieu bie'n logic A, B, C... Bie'n ra: Q = A © BffiC© ... = [(A © B) © C] ©... Dua tren ti'nh ke't hap cua phep ti'nh HOAC - LOAI TRlT, nen mach XOR ba diu vao (Ki hieu a hinh l-19b) se gfim hai phin tir khOng tuong ducrng noi ting vdi nhau (hinh l-19a). A©B©C A©B©C a) b) Hinh 1-19.Thanh lap mach XOR ba dau vao Quy tic tinh gia tri bie'n Q 6 diu ra mach XOR nhieu diu vao nhu sau : Q se bang 0 khi s6' bie'n vao mang gia tri 1 la mOt s6 chan ; khi s6' bie'n vao co gia tri 1 la mot s6' le thi Q = 1. VI du : Dua vao quy tic tr£n, ta co the lap bang chan If cua ham XOR vdi ba bie'n d6c lap A, B, C (bang 1-9). Bang 1-9 A B C Q = AffiBffiC 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1 0 0 1 1 0 1 0 1 1 0 0 1 1 1 1 M6t ling dung cua mach XOR nhi£u diu vao la lam mach tao va ki£m tra tinh chdn cua kenh truyen tin song song. Khi truyen song song thong tin n bit (xem phu luc 2) ta cin kie’m tra xem thdng tin nhan dugc co dung khong. Mot phucmg phap ki^m tra dan gian nhi't la them vao kenh truyen mot bit, goi la bit kiem tra K. Bit kiem tra phai co gia tri 0 hoac 1 the nao de so bit mang gia tri 1 (ke ca bit kiem tra) trong kenh truyen la mot so chin. Nhu vay o noi phat tin phai co mot mach de tao bit kiem tra sao cho bao dam tinh chin cua kenh truyen. 6 noi thu cung cin dat mach kiem tra tfnh chin cua thong tin nhan duoc. 25 Tir tfnh ch at cu a ham X O R n h ieu bien la : K hi so b ien d o c l U iHmin) va g ia tri cuc dai cu a m iic tha'p d d iu ra n h o hem d d iu vao (U oLmax < U,Lmax). L am n h u vay n h am b ao d am m a c h co d o 6n dinh nhiSu thi'ch d an g (h in h 1 -2 1 ) Hinh 1-21. Cac mire logic d dau ra va dau vao mach logic. • D o o n d in h n h ie u M la gia tri d ien ap n h ieu toi d a ch o p h ep x ep c n 6ng len m uc lo g ic d dau vao m a k h o n g gay sir tac d o n g sai c u a m ach. K h i sir d u n g , cac ph an tu lo g ic th u d n g d u g c n o i tin g vdi n h au : tin h ieu ra d tin g tra d e la tin hieu vao cu a tan g sau. D o do n eu cac p h in tir th u o c cu n g m o t ho, vdi q u y d in h 28 nhung gidi han khac nhau cua cac miic logic a diu ra va diu vao nhu tren hinh 1-2 1, thi dd 6n dinh nhifiu la : M = min )MH, ML) trong do = U0Hmin _ ^iLmin • = UjLmax _ ^oLmax ' Dd 6n dinh nhieu cua cac vi mach sd' rit cao, khoang 10 + 40% dien ap ngudn cung cip. • Cac ddng vao vd ra ting vdi hai mite logic : IiH, IiL, IoL, IoH Trucmg hop dimg cac mach cung mdt ho nO'i ting vdi nhau, co the thay the’ cac thong s<5 dong vao/ra bing khai niem v6 he sd tai dau ra (Fan - out). No la th6ng sd' chi so diu vao nhi£u nhit co the’ nd'i vdi mdi diu ra cua mach cung ho ma khong lam dien ap diu ra chay khoi vung quy dinh cua hai miic logic. He sd tai diu ra cua mach TTL thucmg la 10 (cua mach ho CMOS la tren 50). Hinh 1-22. M6 ta trS truySn dat cua phin td DAO • Tri truyen dat t^ , hay con goi la toe dd chuyen mach, dac trung cho sir ch4m tre cua viec thay d6i trang thai cua tin hieu d diu ra theo su thay doi trang thai tin hieu d cac diu vao. Hinh 1-22 md ta tre truyln dat cua phin tir DAO. 1-10-3. Mach logic ho TTL a) Ki hieu vd cac thong sd cua ho TTL Ho TTL co.haijihdm co ban la nhom 74 dung trong thuong mai, con nhom 54 dung trong quin su. Diem khac nhau chinh gifla hai nhom nay la gidi han nhiet dd lam viec : Ddi vdi nhom 74 la 0 70°C, vdi nhom 54 la -55 + +125°C. Trong mdi nhom lai cd nhilu chung loai dac biet, nhim tang td'c dd chuyen mach va giam cdng sui't tieu thu tit ngudn cung ci'p 1C. Quy tic ki hieu cac ho IC TTL nhu sau : 74/54 ..............., xxxxxxxxxxxxxx vai chu cai vai con sd 29 T rong kf h ieu tren , vai c h u cai de chi cac ch u n g lo ai n h u : N - th o n g thucmg (N o rm al), H - toe do c h u y en m ach cao (H ig h sp eed ), L - tie u th u c o n g s u it th ip (L ow p ow er), S - m ach co dun g diod S chottky n o i g iu a cuc go c va g o p nen t ^ giam khoang 3 lin , L S - tieu th u cong s u it tha'p va co diod S ch o ttk y (L o w pow er S chottky), A S - t6'c do c h u y en m ach n h an h hem lo ai co d io d S ch o ttk y (A dvanced S chottky), A LS - cong sua't tieu thu tha'p va tefc dd c h u y en m ac h n h a n h hem loai LS (A dvanced L ow p o w er S chottky). V ai con s6 n am a cu<5i cu n g chi chiic nang cua IC, vi du m ach N A N D , N O R , m ach dSm , g iai m a... Bang 1-10 cho cac th d n g s6 cu a IC ho TTL. T ro n g b an g c h ieu ducm g quy uoc cua dong dau ra va dong d iu vao tucrng ling la di ra khoi m ach va di vao m ach. B a n g 1-10 C a c th o n g so c u a IC h o T T L Chung loai N H L S LS AS ALS Cac thong so \ s Bien ap cung cap (V) Miic logic dau ra 5 ± 2,5% 5 ± 2,5% 5 ± 2,5% 5 ±2,5% 5 ±2,5% 5 ±2.5% 5 ±2,5% Uoh(V) Uol(V) Miic logic dau vao UH(V) UL(V) >2,4 <0,4 > 2 <0,8 >2,4 <0,4 > 2 <0,8 >2,4 <0,4 > 2 <0,8 >2,7 <0,5 2 2 <0,8 >2,7 <0,5 £ 2 <0,8 > 3 <0,5 > 2 <0,8 ^ 3 <0,5 > 2 <0,8 Bp on djnh nhieu (v) 0,4 0,4 0,4 0,3 0,3 0,3 0,3 Dong dau ra loH(mA) loL(rnA) Dong dau vao WmA) IJmA) 0,4 -16 0,04 -1,6 0,5 -20 0,05 -2 0,2 -2 0,01 -0,18 1 -20 0,05 -2 0,4 -4 0,02 -0,4 2 -20 0,2 -2 0,4 -8 0,02 -0,2 Cong suat tieu thu (mW/phan tu) Tre truyen dat t^ (ns) 30 10 23 1 23 2 20 1 10 6 33 3 10 1.5 4 b) Cac mach ra cua phan tu logic ho TTL. Cac phin tir logic ho TTL co the co m6t trong ba mach ra sau : • Mach ra totem - pole (con goi la mach ra cot cham) Hinh l-23a la md hinh phin tir logic vdi mach ra totem - pole, gdm hai khoa K], K2 dong vao cac muc logic cao va tha'p. Chung la cac khoa transistor va lam viec luon nguoc nhau : cai nay dong thi cai kia ma. Cac tin hieu logic cr cua vao dieu khie’n su dong / ma cua hai khoa. Vi du ne'u md hinh hinh 1 -23a la phin tu VA thi K2 dong, ma khi co it nhit mdt bie’n vao bang 0. KhiA = B = C= l thi K| dong K2 ma. +U T + K/j^ 1 - A Q B C 0 rA ■ Q - i — . B* — CS J Hinh 1-23. Md phong cac mach ra cua phin tO logic ho TTL • Mach ra cuc gop ho (de ngo). Phin tu logic cuc gop ha co mach ra la mot transistor BJT, cuc gop cua no de ha. Khi su dung phai noi dau ra Q (chinh la cuc gop) vai dien ap +U thi'ch hop thong qua dien tra R (1 + 5kfi) goi la dien tra treo cao (hinh l-23b). Phin tu mach ra cuc gop ha co cac uu diem sau : - No cho phep ta thay doi miic logic cao H a dau ra bang cach treo len dien ap +U thich hop. Hon nua khi cin di6u khien tai cong suit (den bao hieu, rale dien tit...), ta co the ndi true tiep diu ra vai tai va dat vao dien ap tai yeu ciu (trong pham vi cho phep, thuefng la < 15V hoac < 30V). - Cac phin tir cue gop ha co kha nang thuc hien ham VA noi day (wired AND); nghla la : D e lam phep nhan logic giua nhung bien ra cua cac phan tu cuc gop ha, ta chi cin nd'i chung tit ca cac diu ra vci nhau va treo len muc logic cao +U (hinh 1-24). 31 Hinh 1-24. Thuc hi$n ham VA nd'i dSy cua cac phdn tCt ci/c gop hi3. Tir h in h 1-24 ta tha'y : Ne'u m d t tro n g cac tra n sisto r d iu ra d in bao h o i, n g h la la chi c in m d t d iu ra Q; = 0 lo g ic (i = 1, 2 ......n) th i Q = 0 lo g ic ; chi khi t i t ca cac tra n sisto r deu k h o a (Q j = Q2 = •••Qn = 1 lo g ic) th i Q = + U = 1 logic. V ay Q = Q, . Q2 -Q„ • M a c h ra ba tr a n g th d i. C) p h in tu lo g ic vdi m ach ra ba tra n g th a i, d iu ra Q co the n im cr ba tran g th ai sau : H ai tran g th ai, ting vdi m iic lo g ic 1 h o ac 0 k h i p h in tu lam viec. N goai ra con cd the cd trang th ai thu; ba, go i la tran g th a i to n g tr d ca o (h o ac tr a n g th d i treo ), luc dd d iu ra Q coi n h u tac h r&i khoi p h in tu. H in h l-2 3 c m d ph o n g p h in tu lo g ic vdi m ach ra 3 tran g th a i la h ai khoa K ^ K 2. K hi p h in tu h o at d d n g , hai k h o i lam viec n g u o c n h au , m d t cai d o n g th i cai k ia m d th eo sir d ieu k h ien cua tin h ieu vao A , B. T u j' th e o vi tri cu a h ai khoa m a Q se bang 0 hay 1 logic. T u y vay, m ach co n co th e cd tran g th a i th u b a (tdng tra cao) irng vdi kh i K j, K 2 d£u m o, d iu ra Q coi n h u ta c h ra k h o i m ach . T in hieu a d iu CS, goi la d iu chon "chip", dung de di£u khi£n m ach 6 trang thai th u ba nay : K hi CS = 1 (hoac 0) th i h ai k h o a deu m o , do c lap v6 i cac tin h ieu vao A , B. Q = A Q = A a) b) c) Hinh 1-25. Ki hi$u cac phan tCt <3&m ba trang thai va phin tCr <3&m hai dau ra. 32 Ngudi ta c6n hay san xua't cac IC dem (buffer) ba trang thai. No thuc chi't chi la mdt khuech dai logic ba trang thai, kf hieu nhu a hinh l-25a, b. Khi E = 1 (hoac E = 0 ddi vdi hinh l-25b) thi Q = A ; khi E = 0 (hoac E = 1 ddi vcri hinh l-25b), phin tu dem se a trang thii tdng trd cao, diu ra Q tach khoi diu vao A. Vay vai trd phin t i dem tua nhu mdt khoa co khi dong cat. Cung cin phan biet kf hieu phin tit dem 3 trang thai vdi phin tu dem co hai diu ra dao va khdng dao d hinh l-25c. iTu di^m ndi bat cua cac IC logic vdi mach ra ba trang thai la ta co the nd'i cac diu ra cua IC len cilng mdt kenh truyln chung. Dilu nay lam don gian ra't nhieu cho viec tao lap kenh truyln sd lieu trong mdt he tho'ng logic. Hinh l-26a la vf du \ i nd'i ba "chip" nhd RAM mach ra ba trang thai len cung mot kenh truyen chung 4 bit. V i hinh thuc thi cac diu ra cua mdi bd nhd deu dugc noi cling (noi vat If) vdi kenh truyen chung. Nhung bang cach chon dat len cac diu chgn chip CS cua IC nhung miic logic thi'ch hgp, ta ludn bao dam tai mot thdi di£m chi cd mdt IC nao dd trong ba IC dugc nd'i vdi duong truyln chung, cac IC khac deu d trang thai treo, tach khoi dudng truyen. Vay, diu dieu khie’n trang thai treo CS cua cac IC ba trang thai cd kha nang dieu khien du&ng BUS (kenh truyln). Kenh tnjyen chung a) b) Hinh 1-26. Noi cac IC ba trang thai vdi k§nh truyen chung va cong truyen hai chiSu ba trang thai. Hinh l-26b chi ra mot cach nd'i cac phin tit dem ba trang thai de tao thanh cdng truyen logic theo hai chieu. Khi E = 1, phin tit dem so 1 thdng, phin tu dem so 2 treo, tin hieu truyen tir B sang A ; khi E = 0, phin tu 2 thdng, phin tit 1 treo, tin hieu di tit A sang B. 3 - GTKTD 33 1-10-4. M a c h lo g ic h o C M O S a) C a c th d n g so c u a IC h o C M O S N h in ch u n g n h i6u th d n g sd cu a m ach ho C M O S td t h a n cu a m ach ho TTL. D o d o cac m ach SSI, M SI h o C M O S hien nay rat th d n g dung. • D ien ap n g u o n cu n g ca'p +3 + + 15V • C) che d d tin h (k h i tin h ieu a cac dSu vao va ra giu: dn d in h a m d t miic lo g ic), m ach hau n h u k h o n g tieu thu cdng sua't tir n g u 6n c u n g ca'p (P cc = 0,01 I^W /phan tu). N h u n g d ch e do don g (k h i tin hieu a cac dau vao va ra lien tuc ch u y en qu a lai g iu a hai mire lo g ic), co n g sua't m ach tieu th u tir n g u 6n cu n g c£p tang ti le v ai tan so lam v iec cu a m ach. • D o dn dinh n h ieu cao. V di n g u d n cu n g ca'p + 5 V , d d dn d in h n h ieu cua m ach ho C M O S k h o an g 1,5V . • D ong vao m ach C M O S ra't n h h o , ch i c d p A trd x u d n g (IjHmax * lj*A, liLmax = ~ lH A )- C5 m ach ho C M O S cung khong cd su ch enh lech ld n giua dong ra d miic logic cao (I0h ) va dong ra d mire logic tha'p IoL. T hudng I q h * 0.2 0,5mA, IoL ~ —0,2 + —0 ,5 m A . • M ire lo g ic : Mu:c cao d dau ra U oH a U c c (d ien ap n g u d n cu n g ca'p) ; m ile tha'p d d£u ra u oL * ov. M ire cao d d iu vao U iH > U c c - U K ; m iic tha'p d d iu vao U iL S U K, trong dd : U K a 1,5 - 2V la d ien ap k h o a cu a tra n sisto r M O S. V i du vdi ngudn cung ca'p U c c = + 5V va U K = 1,5V thi U q h * 5V , U q l ~ 0V, U iHmin K 3 ,5 V , U iLmax a +1,5V . • N huoc die’m ch u n g cua ho C M O S loai th d n g th u d n g la tre tru y e n dat ldn (tpd * 50 100ns). b) C ac m a c h ra c u a h o C M O S H ien nay cac IC lo g ic ho C M O S vdi m ire d o tfch h o p n h d va tru n g binh (SSI, M SI) cd ba loai m ach ra : M a c h ra th d n g thucrng, m a c h ra co m a c h dem , m a c h ra ba tr a n g th d i. M ach ra ba tran g th ai d a trin h b ay d tren . K h ac n h au ca b an giira m ach ra cd m ach d em va m ach ra th d n g th u d n g la d o n g ra d m a ch ra cd m ach d em ldn, cd k h o an g vai m A . c) P h a n loai cac IC h o C M O S .Co the chia cac IC ho C M O S thanh hai loai : • C ac m ach C M O S to e do ch am ho 4 0 0 0 va 74C . C ac ho n ay cd d o 6n din h nh ieu ra t cao , t r i tru y en d a t ld n (3 0 + 100ns), d o n g ra n h d (k h o an g 0,2 4- 0 ,5 m A ). 34 • Cac mach CMOS tdc dd nhanh ho 74HCT, 74AHCT, 74HCTL, 74HC. Dien ap cung ci'p thucmg la +5V. Ho 74HC co tri truyen dat t^ » 8 + 9ns, dien ap cung ca'p 2 + 6V, dong ra co 4mA. Ho nay khdng hoan toan tucrng thi'ch vdi ho TTL vi co miic logic d diu vao khac vdi IC ho TTL. Cac ho 74HCT, 74AHCT, 74HCTL la nhung ho dung ra't tuong thi'ch vdi IC ho TTL. Vi du ho 74HCT co UiLraax = 0,8V ; UiHmin = 2V ; IoL = = -4mA ; IoH = 4mA ; tpd = l°ns. Phu luc 6 gidi thieu mdt sd' IC SSI ho CMOS. 1-11. NHdTNG CHO f KHI SCr DgNG CAC IC LOGIC Khi sir dung cac IC sd ta cin chu y nhung diem sau : 1. Khong detu do cac dau vao khong dung tdi Khi xay dung cac mach logic, nhifiu khi ta phai dung cac phan tu co sd' diu vao nhieu han yeu ciu, nghla la co mdt sd chan khong dung tdi. Ne'u de ho cac chan nay d ngoai trcri, do nhieu chung co the tu dong nhay len miic cao hoac a viing khdng xac dinh giua hai muc logic. Ret qua co the’ dan tdi su tac dong nhim cua phin tu. Do do nhat thiet phai nd'i cac diu tu do vdi mdt miic logic thi'ch hap sao cho khdng lam thay ddi hoat ddng cua phin tu. Hinh 1-27. Noi diu fi/ do cCia phin tCl VA v& phin tCl HOAC Hinh 1-27 la cach nd'i diu tu do C cua phin tu HOAC va phin tu VA. Cd the’ nd'i diu tu do C vdi mdt trong cac diu vao dieu khie’n A hay B. Tuy nhien khdng nd'i nhu the' vi : • Lam nang them tai cua ngudn tin hieu dilu khi£n. • Lam tang dien dung diu vao, do dd lam tang tre truyln dat t^ , nhi't la ddi vdi cac IC ho CMOS. 2. Khi co dau vao sdn sang co the phai dat vao muc thap L thdng qua khoa K (vi du diu C d hinh l-28a), thi binh thudng no phai treo len miic cao H thdng qua dien trd treo cao R khoang 4,7kH (doi vdi phin tu ho TTL), hoac khoang 4,7 + 20kQ (doi vdi phin tu ho CMOS). 35 Hinh 1-28. Noi cac d iu vao cho dpi dSl d mCrc L hoSc mire H N e u cd d a u vao sd n sa n g c h o da t a mure lo g ic ca o H th o n g q u a k h o a K (vi du dau C d hinh l-2 8 b ). L uc do ta kh&ng ndi d iu C vdi mire tha'p (" m a t") th 6ng qu a d ien trd R n h u d h in h l-2 8 b , vi d ien ap ro i I ^ R tren d ie n trd co th£ se kh o n g bao dam d iu C d m ile tha'p (nha't la ddi vdi p h in tu h o T T L ), trircmg hop nay, h o p li nha't nen m ac th eo hinh l-2 8 c . 3. N eu trong "chip" vi m ach ho T T L con thira ra p h in tir lo g ic k h o n g dugc sir d u n g , ta nen treo cac d iu vao cua chung len m iic cao H se g iam d u g c c6ng sua't tieu thu. 4. K hi dun g cac IC ho C M O S ta co n c in luu y cac d iem sau : • C in phong n g u a su d an h thiing cu a ldp o x y t ngan c a c h cuc cd n g va kenh d in cu a tra n sisto r M O S (d ien ap d an h th u n g c0 100V ). Su d a n h th u n g nay co the xay ra do dien tic h tinh tfch tu tren cuc cdng. V i vay kh i b ao q u a n c in phai d at cac "ch ip ” C M O S tren cac g ia d o d in d ien do nh a che' ta o cu n g ca'p k h i ban. • K hi cho cac m ach C M O S lam viec, ta phai d a t n g u d n cu n g ca'p tru 6c, sau do m di dat tin hieu d ieu k h ien len cac d iu vao. K hi cho m ach n g im g lam viec th i n g u g c lai : P hai n g it tin h ieu d at tren cac d iu vao tru d c k h i n g a t n g u 6n cung cap. C ac thao tac nay cung n h am p h o n g ngira su tich tu d ie n tfch co th e xay ra tren cuc cd n g cu a CM O S. • C hu y kh o n g lam ngan m ach d iu ra cac p h in tu C M O S vi tai d ien dung ldn d d iu ra cd the gay d o n g n g an m ach ldn, lam h o n g p h in tu. • K hfing nen n o i so n g song cac d iu vao h oac cac d iu ra cu a cac p h in tir, neu ch u n g k h o n g cu n g nam tro n g m o t "chip". 5. C ac phan tir lo g ic lam viec 6 che' d 6 d d n g lu d n g ay sir bie'n d o n g ld n v i d on g tieu th u tir n g u o n cu n g ca'p. D e g iam h ien tu g n g n ay , ta th u d n g d iin g bien phap "phan tach ng u d n cung ca'p" : N g h la la tren d u d n g cu n g ca'p ch o m 6t vi m ach (card) gdm nhieu "chip", d g in m di nhom tir 4 5 chip ta dat m o t tu cd 1 t lOnF. D dng thdi dat m ot tu loc n g u d n k h o an g vai ch u c |j.F cho to an vi m ach . 1-12. GIAO DI$N GIOA CAC PHAN TlJ HQ TTL VA CMOS Nhieu khi trong m6t he thtfng logic, ta phai phoi hap dung ca cac phin tu TTL va CMOS d& loi dung uu diem cua timg loai. Luc do, thucmg ta khong the nd'i true tiep chung voi nhau ma phai th6ng qua mot giao dien de hoa hap mile logic hoac dong a diu ra va diu vao cua hai ho. 1-12-1. Tririmg hcrp phan tuf TTL dieu khien cac phan tu CMOS • Khi nguon cung cap cho IC CMOS Id +5V, mire cao to'i thieu a dau vao phdn tu CMOS la UiHmin = 3,5V, trong khi mile cao to'i thieu c> diu ra cac phan tu TTL la UoHmin = 2,4V. Vi \&y phai dung m6t dien tra R « 1 lOkQ n6i giua diu ra phin tu TTL va ngu6n +5V (hinh l-29a). Dien tret R nhkn n&ng cao UoHmin c“a P ^ n TTL cho phu hcrp vcti ygu ciu cua cac phin tu CMOS. Phan tu dieu khien TTL co thfe la phin t£r mach ra cuc gop ha, cung co the la phin tu mach ra totem - pole. +5V +5V +^cc a) b) Hinh 1-29. Giao di$n giCfa phan t i dieu khiSn TTL va cac phan tC/ CMOS • Khi nguon cung cap cho IC CMOS khde +5V, giao dien se la phin tu dem TTL cuc gop her voi difin trcf treo cao R noi voi nguon cung cap +UCC cua phin tu CMOS (hinh l-29b). 1-12-2. Truing hap phan tu CMOS dieu khien cac phan tu TTL • Khi dung phdn tu CMOS khong tuong thich de dieu khien cac phdn tu TTL. Neu phin tu dieu khien CMOS co nguon cung ci'p la +5V thi diu ra phin tu CMOS khong du sire tiep nhin dong vao Ion, tuang ung v6i muc logic thip (IiL) cua cac phan tu TTL. Thit viy, neu dung phin tu dieu khien CMOS ho 4000 co dong ra khoang 0,4mA, no khong the nhan dong vao |liL| * 1,6mA cua phin tu TTL loai thong thuang. De giai quyet miu thuin nay co thS dung cac cach sau : - Noi song song nhitfu phin tu CMOS. 37 - D ung p h in tu C M O S co m ach ra dem ; h oac d u n g p h in tu C M O S thdng thucm g noi tin g vdi p h in tu dem C M O S (vi d u IC 4 0 1 0 ). M ach ra cu a p h in tu d em co the n h in 3m A cr d ien ap 0,4V . Hinh 1-30. Giao di$n giCra phAn tCr dieu khiSn CMOS vd cac p h in tCr TTL. Ne'u d ien ap cung ca'p ch o p h in tir d iiu k h iin C M O S k h d n g tucm g thi'ch vdi d ien ap ng u d n cu a p h in tu ho T T L , thi ta phai du n g tra n sisto r B JT n6 i ho a hop hai p h in tir C M O S va T T L (h in h l-3 0 a ). C hu y rin g g iao d ie n tra n sis to r trong h in h ve co vai trd n h u p h in tir D A O p hu them . • N e u d u n g c h u n g lo a i C M O S H C T (vi du 74 H C T , 7 4 H C T L ) th i n o hoan toan tu o n g thi'ch vdi ho T T L v i m iic logic. D ong ra ciia p h in tir C M O S 74H CT cung lcm ( |loH | = |l oL | = 4m A ). D o d o co th e nd'i tru e tie'p p h in tu d iiu k h iin C M O S vdi cac p h in tir T T L vdi he sd' F an - o u t th fch h o p (h in h l-3 0 b ). CAU HOI VA BAl TAP CHlTONG 1 1-1. Xung la gi ? Bir6c nhay la gi ? C a c thong so chinh d ac trung cho mot xung hinh thang va xung rang cifa la gi ? T h e n ao la xung vuong goc ? C ac thong so dac trung cho m ot birdc nhay la gi ? 1-2. C a c thong so d ac trung cho m ot day xung vuong goc tuan hoan ? The nao la day xung vuong goc doi xtfng ? T h e n ao la ca c m ach p hat xung dang chay tir do, the n ao la cac m ach phat xung dang ki'ch khcii ? 1-3. N eu cong thirc (khdng can chiing m inh) ti'nh dien ap tren ca c phan tif m ach R -C khi co birdc nhay dien ap dat vao ; trirdc khi co birdc nhay, dien ap tren cac phan turdeu bSng 0. Thdi gian qua do xay ra trong m ach bang bao nhieu ? 38 5V "0 a) b) c) Hinh 1-31. Bai tap 1-4 va 1-7. 1-4. Cho mach hinh 1-31a. Biet R = 10kQ, C = 0,47 nF. D5t vao mach mot xung vuong goc co do rong tx (hinh 1-31 b). Hay ve dang dien ap ra ur(t) khi tx = 50ms va khi tx = 0,3ms. 1-5. Hinh 1-32a la so do khoa transistor dieu khien dong I md khoa K cua role cd dien. Cuon day rdle m ic cl phia cuc gop va co dien trd R = 100Q. Dien ap cac cifc transistor d che do bao hoa la Ube * 0,7V, uce * 0V. Dien ap dieu khien transistor uv co hai mi/c : mire thap L = 0V, mtic cao H = 6V. He so khuech dai dong cuc tieu cua transistor Bmjn = 100. Giai thi'ch hoat dong cCia so do va tinh dien trd Rg, chon he so bao hoa Kbh = 2. +12V +Ua R, ■ ur = uc Hinh 1-32. Bai tap 1-5 va 1-6 39 1-6. Hinh 1-32b la so do khoa transistor v6i tai la dien tro R t (hoac R ,). Giai thich anh hirdng cua dien trd tai tcii sir lam viec cua khoa trong hai truong hop : • T ai Rt m ac song song v6i R c ; • T ai R t noi "mat". 1-7. M ot khuech thuat toan lam viec a che do khoa vdi nguon cung cSp ± U c c = ± 12V (hinh 1-31c). D ien ap bao hoa ± U bh = ± (U c c - 2 V ). Hay Lfdc tinh thdi gian qua do t<}m khi khoa chuyen trang thai trong hai tn/dng hop : • Khuech thuat toan la nA741 co toe do xoay S R = 0 ,5 V /^ s. • Khuech thuat toan la L M 3 1 8 co S R = 70 V /^ s. G ia dinh khuech thuat toan co he so khuech dai vi sai A D = 106 . Lfdc tinh do nhay cua khoa. 1-8. M ach logic la gi ? C ho vai vf du ve m ach logic. Mure logic la gi ? T h e nao la m ach logic duong, logic am ? Phan biet giOra m ach logic to hop va m ach logic day ? 1-9. T h e nao la m ach logic ho T T L , ho C M O S ? Uu nhuoc diem cua m oi ho. 1 -1 0 . T h e nao la phan tur logic cifc gop d e hd, the n ao la phan ti!r logic ba trang thai ? l/u diem ctia cac phan tCf nay. 1 -1 1 . Neu cac thong so dac trutig cua vi m ach logic. 1 -12. Cho m ach hinh 1-33. V ie t bieu thtrc logjc.cda Q 1t Q 2. G iai thi'ch. Hinh 1-33. Bai tap 1-12 1 -13. Hinh 1 -3 4 a , b, c la cac m ach logic role (h ay con goi la cac m ach logic tiep d iem ), trong do A, B la cac bien logic d ac trtfng cho hai trang thai dong / m d cua cac khoa co khi. Hinh 1-34d , e, f la cac m ach logic dien ttr, trong 40 do A, B la cac bien logic dac trung bdi cac mire logic dien ap cao va thap. Hay chuirng to mot cach dinh tinh ring cac mach 6 hinh 1-34 chinh la ba phan tur logic co ban. Q = A.B A, Q = A+B -=TE ■±r E Q= A 9 * r A-------KF Q= A.B D Hinh 1-34. Bai tap 1-13 1-14. Tim to hop ma nhi phan b1b2b3 de thuc hien : • Md cdng HOAC d hinh 1-35a, cho thong tin A di qua. • Dong cdng VA d hinh 1-35b, chan lai thong tin A. • Dau ra phan tir khong tuong duong d hinh 1-35c co Q = A • Dong cdng HOAC 6 hinh 1-35d, chan lai thong tin A b,-g Di — Hinh 1-35. Bai tap 1-14. 41 1 -1 5 . V iet bieu thtjfc logic cua bi£n ra Q d hinh 1 -36a va ch? ra vai trd cua m ach dung de lam gi ? 1-16. X ay dung m ach logic sao cho dau ra Q la d mCrc cao H, neu cac dau vao A, B, C deu d mCfc cao ; hoac neu cac dau vao D, E, F la cung 6 m iic cao. 1 -1 7 . X a y dung m ach logic sao cho dau ra Q se d mure cao H, khi m ot trong hai dau vao A va B la cl mUc cao (nhung khong phai ca h ai) ; h oac m ot trong hai dau vao B, C (nhung khong phai ca hai) la d mUc cao. +5V 1KO S = 3 E > - “i = E > i b) K 7Kn : = E > - a) i 2 v - r r Hinh 1-36. Bai tap 1-15 va 1-19 5KO c) 1 -1 8 . V ie t cac bieu thifc logic bieu thi cho cac quan he logic dudi d ay : • BCira an trua horn nay 6 nha m ay g o m banh mi kep thjt v6i m on phu la canh hoac rau tron, nhung khong phai ca hai m on phu. • Ngudi cong nhan co the chon son biJc tuong m au vang va xanh Id nhung khong phai ca hai. N g ay khi anh ta khong son tuong thi cung phai son tran m au trang. 42 • De qua di/dc ciia vao cau lac bo, anh phai tra 3000d va xuat trinh the hoi vien, ho3c anh phai tra 40003. • Neu muon hoc giao trinh luat hay sdhoac ca hai, anh con can phai theo hoc mot ngoai ngiir Anh hay Phap, nhung khong phai ca hai ngoai ngj. 1-19. Thiet ke he thong canh bao ciia xe taxi 4 cho ngoi. He thong se bao dong bang coi neu nhif co dau hieu chay trong xe hoiSc co hanh khach khong deo chat day an toan cl cho ngoi. Moi cho ngoi cua hanh khach co dat hai mach kiem tra nhir hinh 1-36b ; mot mach de kiem tra si/ co mat ciia hanh khach d ghe ngoi, mot mach de kiem tra day an toan cl ghe ngoi co di/oc sir dung hay khong. Khi co hanh khach 6 ghe ngoi(hoac khi day an toan diroc dung) thi khoa K dong lai. Hinh 1-36c la mach phat hien chay. Khi co dau hieu chay trong xe thi khoa K dong lai. Sir dung day xung vuong goc tan so 2KHz lam coi bao dong keu moi khi co si/ khong an toan trong xe. 43 CAC MACH TAO XUNG HOAC ■ ■ BlTCJC NHAY DUNG TRANSISTOR HAY KHUECH THUAT TOAN 2-1. MACH SO SANH Tl/ONG TU’ • M ach so san h ch o m ot bucrc nhay dien ap a dau ra de; chi k e t q u a so sanh gitfa hai dai lu o n g a cira vao. C o hai loai m ach so san h : - M ach so sanh hai so nhi phan, goi la m a c h so sa n h so, se trin h bay 6 ch uong 4. - M a c h so s a n h tu o n g t u so sanh m o t dien ap v<5i d ien a p chuS n co do 1dm xac djnh trudc. • N h u da noi 6 tren , m ach so sanh tu o n g tu dun g de’ so san h d ie n ap vao uv voi m ot dien ap chuain co do lcrn dinh trudc Uch. K hi u v = U ch th i d ien ap ur 6 dau ra m ach so san h se ch u y en tir mire cao H x u o n g mire th a p L h ay n g u o c lai. V ay tin hieu a dau ra m ach so san h tu o n g tu la tin h ieu lo g ic, c o n tin h ieu a dSu vao la tin hieu tu o n g tir (an alo g ). • H ien nay, phan tir c o ban dun g lam m ach so san h tu o n g tu la k h u ech thuat toan, lam viec o che d o kh o a. Vi vSy, cac th o n g so d ac tru n g ch o m a c h so sanh cung ch in h la cac th o n g so dac tru n g c u a k h o a k h u ech th u a t to an , d a trin h bay a m uc 1-5-2, gom : - D o nhay m ach so san h , chi'nh la d o nh ay Au ciia k h o a k h u ech th u at toan (xem hinh 1-1 lb ). - Thfri gian lat trang thai cua mach so sanh. No chi'nh la thdi gian dong/mo tdm ciia kh oa k h uech thuat toan (xem hinh 1-1 lc). - Hai mure logic L, H o dau ra mach so sanh thudng cung chi'nh la hai dien ap bao h oa ± U bh a dau ra khuech thuat toan. Neu dung nguon mot chi^u khong 44 ddi xiing + Ucc cung d p cho khu&h thuat toan thi hai miic logic d diu ra mach so sanh se tuong ling vdi miic dien ap OV va mtrc didn ap bao hoa +Ubh = +UCC - (3 ^ 4V). Cung co mach so sanh cho hai miic logic L, H d diu ra co thi lua chon theo ytw ciu su dung, vi du mach so sanh dung IC LM311 se khao sat d dudi. • TTieo ca'u true, mach so sanh tuong tu chia lam hai loai: - Mach so sanh hd (con goi la mach so sanh khdng tri). So d6 cd ca'u true hd, khdng cd sir phan hdi diSn ap d diu ra vl cua vao. - Mach so sanh vong kin (con goi la mach so sanh cd tri hoac trigo Smith). So do cd ca'u true vong ki'n, cd su phan hdi duong cua di6n ap d diu ra vl cua vao. 2-1-1. Mach so sanh hd Hinh 2-1-a, c la hai so dd co ban cua mach so sanh hd : Kilu dao va khdng dao. Uch la dien ap chuin (con goi la ngudng) dl dien ap vao uv so sanh vdi no. Hinh 2-1. So dd va dSc tinh truyen dat cua cac mach so sanh ho. • Xet so do dao d hinh 2-la. Khi uv < Uch thi uD = Uch - uv > 0 va ur = A dud = +Ubh. Tang din uv cho tdi khi uv = Uch + — (Au la dd nhay cua mach so sanh), thi dien ap ra ur chuyen hoan toan sang miic -Ubh : Au ur = ADuD = AD(Uch - Uv) = -A d — = -U bh. He so khue'ch dai vi sai AD cua khue'ch thuat toan ra't ldn nen dd nhay Au chi khoang vai chuc |iV. Gin dung coi Au » 0, mach se lit trang thai khi uD = 0, nghla la uv = Uch. Ta co dac tinh truyln dat ur(uv) cua mach so sanh dao nhu d hinh 2-lb. Neu tiep tuc tang uv vum qua nguong Uch thi ur cung chi duy tri d 45 m uc - U bh. B ay gior ta lai g iam u v. C ung li luSn tu o n g tu , u r se d u y tri 6 mtic —U bh td i khi uv = U ch - 4 ^ (gdn dun g coi u v = U ch) th i m ach se h o an to a n lflt san g m uc + U bh. N eu tie'p tuc giam uv, d ien ap ra u r van d u y tri 0 + U bh. X et s o do k h o n g dao h in h 2 - lc , ta thfl'y : u D = u v - U ch C ung If luan n h u tren va coi Au » 0, ta co d ac tin h tru y e n d at u r(u v) cua m ach so san h khong dao n h u a h in h 2 - Id. • M ach so san h h o co hai n huoc di^m ch in h : - D o nhay Au va th a i g ian lat tran g th ai tdm cu a m ach k h d n g du n h o kh i co yeu cau cao. - N guong dong U d va n g u o n g m o U m cu a m a c h so sa n h la n h u nhau va bang U ch, (U d = U m = U ch). D o vay m a ch lam viec k h 6ng 6n d in h k h i co tac d o n g cua nhiSu. T a h ieu n g u o n g d o n g U d la n g u d n g d ie n a p d£ m a c h so sanh ch u y en tu tran g th ai m o, irng vdi ur = -U bh, san g tran g th a i d o n g voi u r = + U bh. N g u o n g m o U m la n g u o n g d ien ap de’ m ach c h u y e n tir tran g th a i d o n g sang tran g thai m o D e k h ac phuc hai nhucrc d iem tren , n g u d i ta d u n g m ach so sa n h co tri, thuO ng goi la trig o Sm ith. 2-1-2. Mach so sanh co tre (trigo Smith) M ach co ca'u tru e vong k in vdi ducmg p h an h 6i d u o n g n e n th u c d£y nhanh q u a trinh ch u y en tran g th ai ; d ac tin h tru y d n d at co n g u d n g m o va n g u o n g dong phan b iet (U d * U m). +Ubh Ua u v •Ubh So do daob) c) d) So do khong dao Hinh 2-2. So c16 va dSc tinh truyen dat cCia cac trigo Smith. H in h 2 -2 a, c la h ai so d 6 co ban cu a trig o Sm ith du n g k h u e c h th u a t to an : So d6 dao va so do k h o n g dao. 46 • Xet so d6 triga Smith dao d hinh 2-2a. Ta tha'y mach co dudng phan hoi duong, vdi dien ap phan hdi: Uf * U' R ^ V nen dien ap ra ur chi co th^ d miic -Ubh hay +Ubh. Mat khac, ne'u coi dd nhay Au » 0, thi khi uv = Up mach se lat trang thai, chuyen tir +Ubh sang -Ubh hoac nguoc lai. Ne'u mach dang d trang thai dong vdi ur = +Ubh thi ngudng mor cua mach la : A . Um - U P I ur=+Ubh - +Ubh n . r, (2-1) Rj + R-2 Khi mach dang a trang thai md vai ur = -Ubh thi ngudng ddng cua no la : u d= UP| u =_Ubh = -U bh (2-2) . Nhu vay ngudng dong va ngudng md cua triga Smith dao ti'nh theo (2-2) va (2-1) la phan biet nhau (bang nhau ve dd ldn nhung khac da'u). Dac tinh truyen dat cua triga cho d hinh 2-2b. Ta tha'y, khi uv < Um triga d trang thai ddng vdi ur = +Ubh ; tdi khi uv > Um, triga chuyen sang trang thai md vdi ur = -Ubh. Luc nay, de triga quay ve trang thai ddng thi yeu ciu uv phai bang hoac nhd han ngudng ddng U^. • Xet trigo Smith khdng dao d hinh 2-2c. Mach co phan hoi duong vdi dien ap phan hdi R, Uph = ur R| + R2 va no se lft trang thai khi uP = 0. Dac tinh truyen dat cua triga cho d hinh 2-2d vdi ngudng ddng: R, u d - + u b h ^ (2-3) va nguang ma Um= -U bh^ (2-4) Hinh 2-3a, b tuong ring la ki hieu cua cac triga Smith khong dao va dao trong cac sa dd dien tu. 47 Hinh 2-3. Kl hi6u cua cac trigo Smith 2-1-3. Vai vi mach so sanh a) V i m a c h L M 3 1 I la "chip" khu ech th u at to an td'c dd cao , c h u y e n dung lam khoa. V o ki£u DIPS v6i 8 chan, ch an 5 kh d n g sir d u n g (h in h 2 -4 a). • M ach ra cua L M 3 1 1 la m dt transistor B IT, cuc gop h a (xem m uc l-10-3b). C ue phat tran sisto r nft'i v6i ch an s6 1, go i la ch an "m at". K hi sir d u n g , ch an nay p h ai n6'i "m at" hoac nfi'i voi m 6t dien ap tu y chon. DSu ra 7 chi'nh la cu e g o p d^ her cua tran sisto r T. K hi sit du n g phai n6'i dau ra 7 voi d ien ap + U tu y ch o n , thong qu a "dien trcr treo cao" R k h oang 1 + lO kQ . V iec k h o a h ay dSn bao ho& cu a T tu y thudc q u an he g iu a u N va u p a cu a vao : N eu Up < uN, tra n sisto r T dan bao hoa, d ien ap ra u r a m u c tha'p L , bang d ien ap d at vao chan 1 . Ne'u up > uN, tra n sisto r T bi k h o a, d ien ap ra u r a m iic ca o H , b a n g +U . © 8» +U n n n n n n n -U cc a) b) Hinh 2-4. Vi mach LM311 va 4584 • C han 6 la chan d ieu k h ien ch o p h ep L M 311 lam viec. N eu n 6 i ch an nay vdi dien ap d u an g hoac de h a th i m ach lam viec n h u da mfl ta a tren . N eu n 6'i chan 6 vdi "mat" thdng qua mdt dien trd thi transistor T luon khoa va dien ap ra ur luon d miic +U, ddc lap vdi cac dien ap d cira vao. • Ngudn cung ca'p ±UCC = ± 15V. Cung co th£ dung nguon +5V. Luc do chan 4 nd'i "mat". b) Vi mach 4584 thudc ho CMOS (xem 1-10-4) gdm 6 trigcr Smith dao. Dien ap nguon cung ca'p la 3 + 18V. Hinh 2-5. Thanh lap trigo Smith tit NAND c) Cd the thanh lap triga Smith khdng dao tir hai phin tir NAND ho CMOS (hinh 2-5). Ti sd R2/R[ = 10. 2-2. ONG DVNG COA MACH SO SANH TL/ONG TI/ Dudi day la vai ling dung chi'nh cua mach so sanh tuong tu. 1. Dung phat hien va bao hieu khi mdt dai lumig vat li cin theo doi da dat tdi gia tri ngudng. (0 chuyenKhuSch u( E > dai + ? Hinh 2-6. Mach phat hi$n ngudng cua nhiet d6 do Hinh 2-6 cho mot vi du v6 mach bao hieu khi nhiet dd t° dat gia tri ngudng. Dien ap diu ra mach khuech dai u(t°) duac so sanh vdi dien ap chuin Uch. Tri 4. r.TKTn 49 S(^ ^ ch chon tu o n g irng vdi dien ap diiu ra m ach khue'ch d ai d n h ie t do ngtfdng, vf d u 500°C : U ct) = u (500°). K hi nhiet dd d at n g u d n g , d ien ap ra u r ciia mach so san h n h ay tir -U bh len + U bh. 2. D im g m ach so san h de bien m dt d ien ap bien th ien ch u ki th eo th d i gian th an h day xu n g vudng goc cung tin sd. Vi' du de do t^n sd cac d ao d d n g chu ki bang phuong p h ap sd (xem m uc 1 0 -2 ). Vf du. Cho m ach hinh 2-7a. Bie't R , = 5 k Q , R2 = 2 k Q ; diSn ap ra bao hoi ± U bh = ± 10V . D iSn ap vao u v = 6 sincot (V ). H ay ve d d thi th d i g ian cu a d ien ap ra ur(t). Hinh 2-7. Bien dao ddng hinh sin thanh day xung vu6ng gt>c T a tha'y hinh 2-7a la trigo Sm ith dao, co dac tinh truyen dat n h u hinh 2-2b, vdi : R 2 n g u d n g m d U m = + U bh R +2R ^ = 10 a + 2 ,9 V , R 2 n g u d n g d o n g U d = - U bh +2R ^ = - 1 0 » -2,9V . V di u v = 6sincot (V ), ta ve d u g c dd th i th d i g ian cua ur(t) n h u d h in h 2-7b. N h an xet tha'y d ie n ap ra la d ay xun g vudng goc cung t5n sd' vdi d ao d d n g hinh sin d dau vao. 2-3. MACH TAO XUNG DON DCJNG TRANSISTOR M ach tao xung d o n , hay co n go i la m ach da hai m dt tran g th ai dn d in h . N o la mach ma khi hoat d o n g , dau ra lu d n nam d m dt tran g th ai dn d in h . vi du m ire 50 tha'p L. Luc co mflt xung kfch thi'ch 6 diu vao, dien ap diu ra chuyen sang trang thai kh6ng 6n dinh (vi du rniic cao H) trong mOt thoi gian, r6i lai tu dong quay \6 trang thai 6n dinh cua no. Nhu viy, ling voi mflt xung ki'ch thi'ch cf diu vao, mach cho 6 phi'a diu ra mOt xung don vuflng goc voi d6 r6ng xung xac dinh. 1. Hinh 2-8a la mach tao xung don, kich thich bang tay. Dien ap ra ur chi'nh la dien ap cuc gop cua transistor T2. • Binh thucmg, khi khoa K ho, difin tro R2 tao m6t dien ap phin cuc du duong tr6n tie'p giap gd'c - phat cua T2 de’ no din bao hoa. Phai chon R2 sao cho thoa man di£u kien d£ T2 bao hoa siu, nghla la : R2 U K a 0 ,6 V Do do T j trd nen dan bao hoa va u c i a 0 ,2 V . T ra n sisto r T 2 c h u y en san g ch£ do khoa vi : UB2 = uc i " UC = 0 ,2 V - U c c + 0 ,7V a - U c c trong do u ^ la dien ap tren tu C trudc khi cac tra n sisto r c h u y e n tra n g th a i, tfnh theo (2-6). D ien ap ra u r nhay len m uc cao H (u r = H « + U cc )- M ach nam 6 trang thai m di nay (T j d in , T 2 k h o a) k h o n g d u o c lau vi transistor T | d in lam tu C dugc nap theo chieu ngugc lai : + U c c —* ^ 2 —* ^ ^1 —> "m at". Do do dien ap cuc g6c uB2 cua T2 se tan g d in tir -U ^ c th e o mute d6 nap cua tu C. K hi uB2 chdm vugt qu a dien ap khoa U K th i T 2 trd ve tra n g thai dan bao hoa, vdi ur = L « 0,2V , va T | lai quay ve tran g th a i k h o a. V ay , ting vdi m ot kfch thfch d ben ngoai (d day la nha'n n u t a'n K ), m ach se c h o d d iu ra m 6t xung vuong goc co bien d6 khoang bang d ien ap n g u o n c u n g ca p ; d 6 rd n g xung tx ti 16 vdi hang sd thdi gian R 2C : tx = R2Cln2 » 0 ,7 R 2C (2 -7 ) • Mach tao xung kfch thfch b an g tay d h in h 2 -8 a ch i th fch h g p d e tao xung co dd r6ng tx khoang vai g iiy trd len, do su ch am trS cu a v iec n h a k h o a K sau m &i lan tM n nut. Cac dien trd R c l , R C2 phai ch o n n h d d£ g ia m su d n len cua xung. Tri s6 di6n hinh cua cac d ien trd tren so d 6 la R ^ j = R ^2 = l , 8k Q , R j = R 3 = R4 = lOkn, R2 = 68k fi. vay, de co x u n g ra vdi d d rCing t x k h o a n g 5s, ta phai chon C = 100(iF. M uon tang do r6ng xung tx len ra't ld n , co 100 s c h in g h an , ta p h ai tim cach tang R 2. X uy nhifcn viec chon R 2 lai bi ran g b u 6c b d i diSu k ie n (2 -5 ). D o d o , d£ co the ch o n R 2 16n, ta phai thay the' tra n sisto r T 2 d h in h 2 - 8a b an g m£>t cap tran sisto r n o i th eo kidu Darlington. T ra n sisto r nd i D a rlin g to n co he s6 khuech dai don g tin h B dat c3104. Vi vay co the ch o n R 2 ld n c a M O . 2. De co d u o c x u n g ta vdi d6 rd n g x u n g ra t h ep , c a m s trd lai, ta p h ai dung m a ch ta o x u n g d a n k ic k thfch ba n g x u n g d a n h (h in h 2 -8 b ). V e co b a n , so do hinh 2 -8b g io n g hinh 2 -8a, nhung th ay vi m ach kfch thfch b an g ta y , ta dun g m ach tao xun g d an h kfch thich(g6m C 3 - R 3 va diod D ). Su h o at d o n g cu a so d 6 tu o n g Hr nhu da d ien d at do i vflisodo h in h 2-8a. 52 Binh thucmg, khi khdng co tin hi6u kfch thi'ch uv, mach R2 - diod D - R3 tao dien ap phan cuc uB2 du duang dI transistor T2 din bao hoa va T, khoa. Dien ap ra nim 6n dinh a mile tha'p (ur = L * 0,2V). Khi dua vao mOt xung kfch thich vufing goc uv co d6 r6ng xung low hem 3R3C3, thi 6 thdi di&n ling v6i suan xilfi'ng cua xung vuflng uv se xua't hien m§t xung danh am uR3 tren dien tra R3 (xem muc 1-3-3, hinh l-6b). Chi'nh xung danh am nay tac ddng len cuc g6'c T2 lam no chuyen tir din bao hoa sang khoa, con T, tir khoa sang dan bao hoa. Mach chi nam o' trang thai khSng on dinh nay, vdi ur = H » +UCC, trong m6t th6i gian phu thu6c vao td'c dS nap nguoc cua tu Cj qua R2. Vay, v6i m6i xung vao kich thi'ch uv, mach se cho a diu ra mot xung vuong goc vdi d6 r6ng : tx = R2C2ln2 * 0,7 R2C2 (2-8) Tri so di^n hinh cua cac linh kien tren so do hinh 2-8b : RC| = RC2 = I,8kn, R2 = 68kfi, R, = R3 = lOkfi, C3 = 2,2nF, diod 1N4148, transistor 2N 3904. Tu C2 chon theo (2-8). 3. Van de cuoi cung cin liru y dien dp cung cap Ucc: Trong cac mach hinh 2-8, didn ap cung cip Ucc khong duac vuot qua +9V, vi khi transistor T2 bat diu chuyen tir din bao hoa sang khoa, tie'p giap goc - phat cua no chiu mot dien ap phin cuc nguoc uB2 a -Ucc. Ne'u +UCC > 9V thi dien ap phan cuc nguoc len co the gay choc thung 16p tiep giap va pha hong transistor. Muon dung nguon cung cip ldn hem 9V, ta dat vao mach cuc g6'c T2 mot diod bao ve (1N4148). Catod cua diod noi vdi cuc goc cua T2. Luc do, giai han dien ap ngudn cung cip chi con bi han che' bai dien ap danh thung giua cuc gop va phat (khoang vai ba chuc volt). 2-4. MACH TAO DAY XUNG VUONG G6C DtlNG TRANSISTOR • Mach tao day xung vuOng goc, hay con goi la mach da hai phien dinh (khong co trang thai dn dinh), la mach ma dien ap a diu ra lien tuc chuyen qua lai giua hai mire cao va thi'p. Nghla la mach cho a cua ra mOt day xung vuong goc voi cac thong so dac trung xac dinh trudc. • Co the dung trigo Smith hoac mach so sanh ho de’ bien mot dao dong tuin hoan hinh dang bit ki thanh day xung vuong goc ciing tin s0' (xem muc 2-2-2). Nhung mach nay dung trong thiet bj so do tin so tin hieu xoay chieu. 6 diy chi 53 trin h bay m d t so d 6 c a ban cu a m ach d a h ai phifin d in h loai ch ay tir d o , khdng cdn cac ki'ch thi'ch a ben ngoai (hinh 2 -9 ). uBit Ub"*’ U«=0,6V Ucc ' ] n r - 2Jaibh Uk * \\J--A~- r X tj / r “•* tx2 — Uqc v a n a) b) Hinh 2-9. Mach da hai phiem dinh dung transistor H in h 2 -9 a la s a d 6 c a ban m ach d a hai phifim d in h d u n g tra n sisto r. K hi m ach lam viec 6n d in h th i h ai tu C ( , C2 lu4n p h ien n h au n ap va p h o n g d ien . Do d o hai tra n sisto r cung lu an phiSn n h au o h ai tra n g th ai d in bao h o a va k h o a. K5t q u a la h ai d ien ap ra u r l , u r2 tren h ai cu c g o p tra n sisto r co d an g n h u n g d ay xung vu d n g go c lech ph a nhau 180° (h in h 2 -9 b ). C ac th d n g s6 cu a h a i d a y x u n g tinh n h u sau : B ien d d xung D o ro n g xung Sucm len C hu ki TSn so U M » + U CC l xi * ° ’7 R i c i ; l x2 * ° - 7 ^ ^ - 2 tri ~ 2.3RC1C2 '• lr2 ~ 2-3Rc2Cl T = t x] + tx2 f = 1/T (2 -9 ) ( 2- 10) Ne'u ch o n R , = R 2 = R , C j = C2 = C, R C1 = R C2 = R c th i ta co h ai d ay xung vudng goc d o i xirng h o an to an giong n h au , n h u n g lec h ph a 180°. (h in h 2-9b). D ien ap cung ca'p U cc co th i tir 1,5V -=- 9V . M uo'n tan g n g u o n c u n g ca p len ta i k h o an g vai ch u c volt, ta phai d at th em h ai d io d IN 41 4 8 vao m ach cu c goc cua hai tra n sisto r. (C) h in h 2 -9 a hai d io d ve ducrng net dirt k h u c, y noi co th e dat th em vao m ach cuc goc). 54 2-5. MACH TAO DAY XUNG VUONG G6C DONG KHU&H THUAT TOAN 2-5-1. So do co ban Hinh 2-10a la so d6 ca ban cua mach da hai phiem dinh dung khuech thuat toan. No g6m trigo Smith dao (xem muc 2-1-2, hinh 2-2a) voi dien ap vao chinh la dien ap tren tu uc, va mach R-C de’ dinh chu ki T cua day xung vuong goc a diu ra. Mach ra ciia khuech thuat toan va R-C hop thanh m6t mach phong / nap cho tu C. Khi uc = u+ thi dien ap ra ur se lat trang thai. 0 b) Hinh 2-10. So do CO ban mach da hai phiem dinh dung khuech thuat toan va md ta hoat ddng ciia mach. Gia sir a thai die’m t = 0, mach dang tir trang thai mo, (ur = -U bh), sang trang thai dong (ur = +Ubh) - xem hinh 2-10b. Luc do, dien ap u+ a ctrc "+" khuech thuat toan se tir nguong dong : chuyen sang nguong mo : 55 D 6ng th d i, tu C du o c nap theo c h ilu ur = + U bb R C —> "m at". D ie n ap UC tan8 ngudng dong U d = -U j theo q u an he ham m u : u c = U bh - (U , + U bh)e-,/RC (2 -1 1 ) T ai then diem t ( , khi uc dat va chdm vuot n g u o n g m o U m = + U j th i d ien ap ra u r lat sang - U bh va u+ lai c h u y ln sang n g u an g don g —U j. T u C b at d5u phong d ie n theo c h ilu : Cue ban phfa phai tu —» R —> m ach ra k h u lc h d a i th u a t toan vdi u r = —U bh -> "m at". K hi phong het th i tu du o c n ap th eo c h ilu c u n g c h ilu ph o n g d ien va uc < 0. Tdi thdi d ilm t2, u c d at va ch d m am h a n n g u a n g d o n g -U ] nein u r lai c h u y ln len +U bh. Q ua trin h cu tiep d ien tu o n g tu va d ie n ap ra la m 6t day xun g vudng goc ddi xtfng, vi hang s6 th a i gian p h o n g / n ap cu a tu la nhu n h au va d iu bang RC. C hu ki T cua day xun g : (2- 12) N eu chon R , = R2 thi T * 2.2R .C . 2 -5 -2 . Mot so so do cai tien • H in h 2-1 la la so d6 m ach da hai p h ilm d in h co th i d ilu c h in h d u o c tSn sd cu a d ay xung ra. Tit cong thtic (2-12) ta tha'y co h ai cach d ie u c h in h c h u ki T cu a d ay xu n g vudng goc d d iu ra so d6 h in h 2 - 1 0 a : - D ieu ch in h hang s6 thdi gian phong / n ap R C cu a tu b an g c a c h th a y dd i R (h o ac C). - D ieu ch in h ti sd hai dien trd R [/R 2 de th ay d d i n g u o n g d o n g U d va n g u a n g m d U m cu a trig a Smith. H in h 2-1 la sir dung c a hai bien phap tren : C h ilt ap R c a i c h ° p h e p th ay dd i h an g so th d i gian phong / nap cua tu. C h iet ap R CA2 c h ° p h e p lam th a y do i nguong dong / m d cua trigo Smith. Neu chon R c a i = 0 100kQ , R^A2 = 0 -s- lOkQ, R ! = 4 7 k fi, R 2 = lO kQ , R 3 = lk f i, C = lO nF, th i th eo (2 -1 2 ), ta co th e d ilu ch in h d u p e tan s6' cu a day xung vudng goc d d i xun g d dSu ra tro n g d a i k h o an g tir 3 0 0 H z d en 5kH z. N goai ra, c h ilt ap R c a 3 = 0 * 1 0kQ c o n ch o p h e p th ay d 6i b ien do cu a day xun g ra. • B ang c ac h tac h b iet rieng hai dudng p h ong, n ap cu a tu , ta se tao ra m ach d a hai p h iem d in h vdi d a y x u n g v u d n g goc k h o n g d o i x im g d d iu ra. C h ilu ro n g x u n g co th e ra t hep. (xem bai tap 2 - 1 1 ). 56 Hinh 2-11. Mdt so so do mach da hai phiem dinh • Cac so do a hinh 2-10a, 2-1 la deu co ngudn cung ca'p ddi xiing + Ucc. Ngudi ta con hay sir dung mach da hdi phiem dinh cd ngudn cung cap khong doi xiing +UCC (hinh 2-1 lb), d so dd hinh 2-1 lb, dien ap ra la mdt day xung vudng goc ddi xung vdi miic tha'p L = OV, miic cao H = Ubh « Ucc - (2 + 3)V. Mach cd phan ap R2 - R3 vdi R2 = R3 = lOOkfl, de tao dien ap mot chieu Ucc/2 d cuc No ling vdi diem giiia ("mat") cua ngudn cung ca'p ddi xiing. Dien trd R2 con cung vdi Rj lam thanh mach phan hdi duong cua triga Smith khdng dao. Ne'u chon Rt = R2 = R3 = IOOKO, thi khi ur = H = Ubh * Ucc, hai dien trd R) va R3 coi nhu noi song song, nguang md cua triga la Um= u+ |Ur=H = 2Ucc/3 ; (2-13) Khi ur = L = OV, hai dien trd Rj va R2 coi nhu ndi song song, ngudng ddng cua triga se la Ud =u+ |ur=0 = Ucc/3. (2-14) Su phong / nap cua tu C qua dien trd R lam cho difn ap ra ur lien tuc lat giSa hai miic L va H mdi khi uc = u . Ne'u coi gin dung dien ap ra bao hoa cua mach hinh 2-1 lb bang dien ap ngudn cung ca'p (Ubh » Ucc), thi ngudng md cua khue'ch thuat toan tinh theo (2-13) va chu ki T cua day xung vudng goc dd'i xiing d diu ra la : T = 2RCln2 » 1,4RC (2-15) Bang cach thay ddi C hoac R hay dieu chinh ca hai, ta cd the thay ddi tin sd day xung ra. Dien dung C cd the nam trong dai tir vai chuc pF den hang nghin nF, dien trd R cd the’ chon trong khoang til lOkQ den vai M£1 57 So d d hinh 2-1 lb co nhuoc d iem sau : - D ien ap ra 6 mire cao H k h o n g chi'nh xac bang + U CC va chu ki T cua day xung ra ti'nh th eo (2 -1 5 ) la khong hoan toan chi'nh xac. - D ay xung vuong goc 6 d iu ra khong that ddi ximg. Chu ki va ti'nh ddi xung cua day xung ra thay doi khi ta thay doi dien ap nguon cung ca'p. - Thcri gian len va xuong cua xung ra tu y thuoc tdc d 6 xoay SR cua khue'ch th u at ♦Ur Hinh 2-12. Mach da hai phiem dinh co khoa transistor dem to an (xem m uc 1-5-2). Ne'u dun g khu ech th u at to an co SR tha'p th i th d i g ian len va xu o n g cua xung ra co the’ tdi hang chuc ^xs. D e khac phuc cac n huoc d iem kei tren ta du n g so d d h in h 2 -1 2 vdi k h o a tran sisto r dem T d dSu ra. T ren so d d ta c h o n R j = R2 = R 3 = lO O kQ. V i tra n sisto r T dao pha dien ap d d iu ra k h u ech th u a t to a n n en d u d n g p h an hdi d u o n g R t - R 2 lai dua vd cuc " cu a k h u ech th u at to an va trig o S m ith th u d c loai kh d n g dao vdi dien ap vao u c.Coi dien ap g o p - p h at cu a tra n sisto r kh i dan b ao hoa bang OV, thi dien ap ra u r la day xu n g vudng go c ddi xim g co m u c tha'p L * OV, m uc cao H a +U CC. T hdi gian len va xu d n g cu a xu n g ch i k h o an g 1 p.s trd lai. Ban doc co the tu phan tich hoat dong cu a m ach h in h 2 -1 2 tren co sd d a nam du p e h o at ddng cua so dd hinh 2-1 lb . 2-6. MOT S 6 CING DUNG COA MACH BA HAl PHI&rf DINH DUNG KHU&H THUAT TOAN M ach da hai phiem dinh dung khu ech th u a t to an th u o n g d u o c sir d u n g de tao d ay xu n g vuong goc tSn sd dudi 100kH z cho n h u n g ung d u n g cu th e. O day se d u a ra vai ling du n g H thu. 1. H in h 2 - 13a la m ot m ach da hai phiem d jn h m a R se giam khi anh san g c h ieu vao m a n h . N g u o n g d d n g / m d cu a trig o Sm ith la : U d = u + |ur = - U bh = ~ U b h /2 U m = u+ |u r= +Uhi = + U b h /2 - 58 Hinh 2-13. Vai ting dung cCia mach da hai phiem dinh DiSm dac biet nha't cua mach la co dien trd RcA. No cung vdi R,), tao thanh mach chia dien ap ra ur, va dien ap tren tu khi <5n dinh : R CA ur = ur c r R,CA + Ra Ta tha'y, ne'u RCA < R^ thi|uc| < |ur /2 |, nghla la uc khong the’ dat tdi ngudng dong / mo cua triga. Dien ap ra khdng thd lat trang thai va khdng cd day xung vudng goc a diu ra. Vay, di£u kien d£ mach da hai phie'm dinh hinh 2-13a) lam viec la : RCA > R f (2-16) Ta sir dung dieu kien (2-16) de’ dung mach (hinh 2-13a) lam mach bao ddng khi cudng dd phat sang cua ddi tuong cin theo ddi vudt qua nguang cua no. Hoac dung lam mach bao trdi sang . Khi trdi con tdi, R^ > RCA nen mach khdng lam viec. Khi trdi sang, R(j> < Rca va mach phat ra day xung vudng goc d ieu khiln coi keu ching han. 2. Ne'u d hinh 2-13a, dem ddi chd hai vi tri cua RCA va R,),, ta se cd mach bao trdi toi. That vay, khi trdi con sang, R(j, < RCA nen mach khdng lam viec. Khi trdi toi, R^ > RCA va mach tao day xung vudng goc d dau ra. Day xung nay vf du dung de dieu khien su chieu sang nha'p nhay lien tuc cua mot mang den quang cao. 0 day, mach cd them vai tro nhu mot rale thai gian, tir dong dieu khien sir nha'p nhay cua mang den quang cao khi trdi toi. 3. Vdi nguyen li hoat dong tuong tu, mach hinh 2-13b dung phat hien nhiet do cua doi tuong can theo ddi khi vuat qua ngudng cho phep. Dien trd nhiet ban dan Rt do nhiet do cua ddi tuong. Khi nhiet do tang thi RT giam. Ban doc tu giai thi'ch hoat dong cua mach. 59 2-7. MACH TAO DAY XUNG RANG CUA VA TAM GlAC C o nh ieu so d 6 tao cac xung rang cu a va tarn g iac : So dd d u n g tra n sisto r, so do dun g k h u ech th u at toan, so d 6 dun g IC d in h th d i 555. d day g id i han trinh bay hai so do c a ban tao day xung tam g iac va ran g cua d u n g k h u ec h th u a t toan. 2 -7 -1 . S o d o ta o d ay x u n g ta m g iac . H in h 2 - 14a la s a d 6 c a ban cu a m ach tao d ay xung tam g iac dung khu ech th u at to an . M ach g6m IC .l la m o t trig a Sm ith k ieu k h d n g d ao (m uc 2-1-2) va IC .2 la m ot m a c h tfch phan. D ien ap d d iu ra trig o Sm ith u rl chi co th e nam d m 6t tro n g h ai m u c bao ho a ± U bh. N g u a n g dong / m d cua trig a tu a n g ling la : U d = + | i - U bh (2 -1 7 ) U m = - | ^ - U bh (2 -1 8 ) — i__i— + \ r 3 - I ri c . r > - iuri r a) Hinh 2-14. Mach tao day xung vuong goc va tam giac M ach tfch phan IC .2 thuc h ien la'y tfch phan cac xu n g vu o n g go c d d i xting den tu trig a va c h o d d£u ra d ay xun g tam giac u r. D ay x u n g nay lai d u a trd ve dau vao trig a Sm ith IC .l d i c h u y e n th an h day xu n g vu d n g go c cu n g ta n sd (x em m u c 2 -2 , h in h 2 -7 ). V ay so dd la m o t m ach tu kfch ch o hai d ay xu n g v u o n g go c va tam g iac c u n g tan sd (h in h 2 - 14b). C) nira chu ki (0 t f), d ie n ap ra u r(t) tang tu y en tfnh th eo q u an he : U h u r( t ) = R ^ t + U m (2 -1 9 ) 60 6 n u a c h u ki t i e p t h e o (!, -4-12). u r(t) g i a m t u y e n t i n h t h e o q u a n h e : (2-20) Ket qua la ur(t) co dang day xung hinh tam giac vdi chu ki : T = 4^ -R ,C (2 -2 1 ) Ta thay, dd diSu chinh tan so day xung ma khong lam anh hudng tdi bien do xung tam giac ta phai dieu chinh hang so tich phan R3C. Mach hinh 2-14a thucmg tao ra cac day xung tam giac va vuong goc trong viing tan so tir vai tram Hz den vai chuc kHz. 2-7-2. Mach tao day xung rang cua Hinh 2-15a la mach tao day xung rang cua, kich khdi (kfch thi'ch) bang day xung danh uv 0 diu vao. So do gom mach bien ddi ap dong IC. 1 va khoa transistor T de dieu khien tu C phong hay nap. Day xung danh uv dieu khien transistor T dan bao hoa hoac khoa. Mach IC.2 la mach lap co he sd khuech dai bang 1 va dien trd vao la oo. Vi vay mach IC.2 chi co vai tro nhu mot phan tir dem, bao dam dien trd tai ciia nguon phat xung danh bang co. nghia la cong suat yeu cau tir ngudn phat xung danh bang 0. Rl ^2 0 nzizi a) Hinh 2-15. Mach tao day xung rang cua. 61 X et sir lam viec cu a m ach hinh 2-15a. G ia sir tai th ai d iem t, x u at h ien m pt xung dan h u v d dau vao, tran sisto r T lap tire d in bao hoa va tu C n h an h chong phong dien qu a T. G an dun g coi hang so thdi gian ph o n g cu a tu b an g 0 nen dien ap tren tu giam dp t ngot v i 0. C ung g in dung coi xu n g d an h chi d ieu k h ien T d5n tire th d i, sau do no lai bi khoa ngay. Vi vay tai t ( tu C b it dau d u o c n ap dien va d ien ap tren tu uc = u+ b it d iu tang (hinh 2 - 15b). IC. 1 la m ach b ien dd i ap - dong, bien dien ap UQ thanh dong ic nap cho tu. N eu dien ap UD la k h o n g ddi thi tu C d u p e nap vdi ddn g khong ddi : *c = I c = U c /R | D ien ap tren tu se tang tuyen ti'nh theo thdi gian : u c (t) = u +(t) = ^ t (2 -2 2 ) D en thdi diem t2, m ot xung danh m di xua't hien, tra n sisto r T d in tire th d i, tu nhanh ch o n g phong d ien he't qu a T va lai dupe nap vdi d d n g k h o n g dd i Ic. D ien ap tren tu lai tang tuyen tinh. Q ua trinh cu: the tiep d ien . T a th a y , cir m di lln x u lt hiSn m ot xung danh thi lai co m ot xung rang cu a h in h th an h tren tu. N eu coi d ien ap tren hai d iu vao IC. 1 la b in g nh au (u + = u ). d ien ap u r d d iu ra m ach hinh 2 - 15a se ti le vdi u+ : u r = u R i ) \ R i V di u+(t) ti'nh th eo (2-22) thi : L M R , + R ,) u r (t) = —2— L----- — t (2 -2 3 ) Rj C V ay, cir m di khi x u it hien m ot xung danh u v d d iu vao, d d iu ra m ach lai ch o m ot xun g rang cua tinh theo (2-23). N eu d d iu vao la m ot day x u n g danh vdi ch u ki lap t , thi ur(t) se la m ot day xung rang cu a co c u n g ch u ki lap t , vdi bien dp : it U 0 (R | + R 2 ) U M = R 2C ■ T (2 -2 4 ) Bien do UM khong the vupt qua dien ap ra bao hoa + U bh cua khuech thuat toan. 62 2-8. MOT S6 UNG DUNG COA DAY XUNG RANG CUA • Day xung rang cua thucmg dung lam "song quet" trong cac thiet bi hien song (dao ddng kf dien tir). Tin hieu cin quan sat ux(t) dira vao hai phien lam lech doc Y cua thie't bi hien song. Song quet uq(t) dua vao hai phien lam lech ngang X (hinh 2-16a). Dudi tac dong cua dien trudng phien lam lech ngang. chum tia dien tir se chuyen dong vdi van toe deu theo chieu true nam ngang. Dirdi tac ddng cua dien trudng phien lam lech doc, chum tia dien tur se bi lai theo chieu true thang dting theo quy luat bien thien cua tin hieu can quan sat. Phoi hop ca hai chuyen ddng tr£n, chum tia dien tu se ve tren man hien song dang tin hieu can quan sat ux(t). Neu chu ki Tq cua song quet bang chu ki Tx cua tin hieu cin quan sat thi tren man hien song se hien mot chu trinh tin hieu quan sat. Neu Tq bang boi sd n cua Tx, tren man hien song se hien n chu trinh tin hieu quan sat. u« _ £ ' Hinh 2-16. Mdt so ling dung cCia xung ring cua • Xung rang cua con dung de chuyen ddi dien ap Ux can do thanh khoang thdi gian ti If tx (hinh 2-16b). Mach phat xung rang ctra cho dien ap tuyen tinh uc(t) = K.t trong dd K la he sd ti le. Khi uc(t) dat gia tri bang Ux thi : Kt* = Ux -*tx = i u x = K u.lJx Do tx se suy ra Ux. Day la mot trong cac phuong phap sd do dien ap. 63 2-1. 2- 2. 2-3. 2-4. 2-5. 2- 6. 64 CAU HOI VA BAI TAP CHl/ONG 2 M ach so sanh tuong tLT la gi ? C ac thong so d ac tri/ng cua m ach so sanh tuong tir ? T h e nao la ngudng dong U a va ngUdng m d U m cua m ach so sanh tuong tu. Trigo Sm ith la gi ? V e so do trigo Sm ith dao, khong d ao va d ac ti'nh truyen dat ctia chung. Uu diem cOa trigo Sm ith so v6i m ach so sanh hd. Trinh bay nguyen li' lam viec ciia m ach tao xung don kfch thi'ch b&ng tay cl hinh 2 -8 a . C an chu y gi khi chon cac dien trd R c1, R c2, R 2 - Gidi han tren ctla nguon cung cap + U CC trong so do la bao nhieu ? T ai sao de tao cac xung don co do rong xung rat Idn thi phai thay transistor T 2 O hinh 2-8a bang cap transistor noi kieu Darlington ? H a y ve hai transistor noi kieu Darlington. Trinh bay n g ln gon nguyen If lam viec cua : • M ach da hai phien djnh hinh 2 -1 0 a . • M ach tao day xung tam giac hinh 2 -1 4 a . • M ach tao day xung rang cua hinh 2 -1 5a. Neu vai Crng dung cCia : • M ach so sanh tUOng tu • M ach da hai phien djnh dung khuech thu at toan. Cho m ach hinh 2 -1 7 a . Biet e(t) = U ms in 314t. H ay ve p h ac do thi thdi gian cCia u-i(t), u2(t) va ur(t), theo do thj thdi gian cua e(t). B iet C = 15nF , R t = 1kn . +12V b) Hinh 2-17. Bai lap 2-6 va 2-8 2-7. Cho mach hinh 2-18. Biet R , = R4 = R5 = 1MC1, R2 = R3 = 1k£i, C, = C2 = 15nF. Oien ap ra bao hoa cda cac khuech thuat toan la ±Ubh = ±10V. Oien ap vao uv = Umsinl00t. Hay ve do thj thdi gian cCia uA(t), uB(t), ur(t), theo do thi thdi gian ctia Uy(t). 2.8. Cho mach H.2-17b. Bi§'t Ri = 10kfi, R2 = 47kfl. Dien ap ra bao hoa cCia khuech thuat toan la ±Ubh = ±10V. Hay : • Ve dac tinh truyen dat ur(uv) cda mach. • Ve do thi thdi gian ur(t) khi uv(t) = 5sin314t (V). 2-9. Cho mach phat xung don hinh 2-19. Hai transistor la loai 2N3904, diod la loai 1N4148. RC1 = RC2 = 1,8k£J ; R, = 68kn ; R2 = R3 = R4 = 10kQ ; C, = C2 = 2,2nF. Mach dtroc kfch khdi bang xung vuong goc uv ci dau vao. Giai thi'ch hoat dong cCia mach va ti'nh do rong cCia xung ddn ur cl dau ra. +9V 5 - GTKTD 65 2 -1 0 . C ho m ach da hai phiem djnh hinh 2 -2 0 a . Biet R Ci = R c 2 = 1 .8 KO ; C i = C 2 = 10nF, R 1 = R 2 = 10kC2, R CA = 0 * 100kQ . H ay chi ra s i/ khac nhau co ban cOa m ach hinh 2 -2 0 a vdi m ach hinh 2 -9 a . Tinh do hong ldn nh3t Qmax (Xem m uc 1-2-1) co the tao d i/d c cua day xung vuong goc d dau ra hinh 2 -20a. +9V Hinh 2-20. Bai t$p 2-10 vd 2-11. 2 -1 1 . C h o m ach hinh 2-20b . Biet R 1 = 2 ,2 k fl, R 2 = 2 2 0 k n , R 3 = 10kf2, R 4 = 1K O , R c a = 0 + 10KC2, C = 10nF. H a y chi ra sir khac nhau cd ban cCia m ach hinh 2 -2 0 b v6i m ach hinh 2- 11a. Tfnh ti s6" giufa thdi gian nghi tn v& do rdng xung tx cCia day xung vuong goc ur ci dau ra. LTdc t(nh dcii tan s6 c6 th£ dieu ch?nh dufgc cCia d§y xung ra. 66 CAC MACH TAO XUNG HOAC Bl/CfC NHAY DUNG CAC VI MACH SO VA MACH DINH THOl 555 3-1. CAC LOAI FLIP-FLOP Flip-Flop la mach logic c6 mflt hoac hai diu vao di£u khi^n, hai diu ra. Tin hieu tren hai diu ra Flip-Flop phu thuOc nhau : Ne'u m6t diu ra co tin hieu la Q, thi a diu ra kia se la phu dinh cua Q (Q). Khi tin hieu 6 cua vao thoa man di6u kien di£u khidn, diu ra Q se lit trang thii tir mtic logic tha'p L len miic logic cao H hoac nguoc lai. Vay, tin hieu 6 diu ra Flip-Flop khi co diSu khie’n la m6t bu6c nhay dien ap. Dac di£m cua Flip-Flop la : Khi khong co dieu khien or cua vdo, mile logic (L hoac H) a dau ra duoc duy tri on dinh. Tuy theo sO' diu vao di6u khi^n, Flip-Flop g6m b6'n loai chi'nh: S-R, J-K, T, D. 3-1-1. S-R Flip-Flop (S-RFF) S-R FF la loai c6 hai diu vio di£u khi^n S, R. Diu S goi li diu vio "ghi" (Set) va R li diu vao "xoa“ (Reset). Hinh 3-la li kf hieu cua S-R FF trong cdc so d6 logic. Trang thai a diu ra Q phu thuOc cac tin hieu logic b hai diu vio di6u khi^n S, R theo bang 3-1, goi li bang trang thii cua Flip-Flop. Bing 3-1 Trong bang 3-1, ki hieu Q(+ chi gii tri logic a diu ra Q sau thcri di^m t, la thdi die’m dit cac tin hieu diSu khi&i logic d cac diu vao S, R. Kf hieu Qt chi gia tri logic 6 diu ra Q tai thdi di£m t. Ta thi'y : Khi S = 1, R = 0 thi Q(t = 1 ; khi S = 0, R = 1 thi Qtt = 0. Diy chi'nh la hai di6u 67 k ien didu k h iln a cu a vao khi£n cho d iu ra Q F lip -F lo p co th i lat tra n g th a i (tir 0 san g 1 h oac ngucrc lai). V i vay S, R goi la cac d iu vao didu k h ie n . C ap S = 1, R = 0 la didu k ien didu k h iln g h i (Q = 1) ; co n cap S = 0, R = 1 la d ie u kien didu k h ien x o a (Q = 0). Tucmg hop S = R = 0 th i Q (t = Q , ; n g h ia la Q khdng th ay dd i tran g thai da co cua no. V ay, khi kh o n g con tin h ieu d ieu khie’n g h i hay xoa a cira vao, F lip -F lo p van g iu n g u y en tran g th ai d a co cu a no. T a n o i, khi S = R = 0 thi F lip -F lo p liru g iu thdng tin. Cud'i cu n g , ne'u S = R = 1, d iu ra Q co th e la 1, cd the la 0 lo g ic ; ta noi trang thai F lip -F lo p la k h d n g x ac d in h . V ay, k h d n g b a o gi& d d n g th o i d a t 1 lo g ic vao S vd R. N h u d a trin h bay a m uc 1-6-3, tro n g cac m ach lo g ic n g u a i ta d u n g tin hieu d ien ap vcri hai mire cach biet nhau la m tic cao H va m iic tha'p L d e d ac trung cho hai gia tri 1 ,0 cua bi£n logic (H —► 1, L -> 0). a) b) c) d) e) f) 9) Hinh 3-1. Ki hieu cac loai Flip-Flop 3 -1 -2 . J - K F lip -F lo p (J -K F F ) J-K F F la loai F lip -F lo p cd hai dSu h) B a n g 3-2 vao d ieu k h ien J, K . K hi J = 1, K = 0 thi Q (+ = 1 ; khi J = 0, K = 1 thi Q t+ = 0. T u y n h ien , d iem dac biet la J-K FT con cd th em d a u vao d d n g bo C va F lip - F lo p chi cd the g h i (hay xoa) trong thoi k h o an g ling vdi su d n len hoac xud'ng cu a x u n g ddn g bo C (con goi la xung n h ip - C lo ck ). T a n o i F lip -F lo p thudc 68 c j K Y nghla 0 X X a . LUu giu 1 X X a . L l Tu giu T(4o 0 0 a , Liru giu t ( i ) 1 0 1 Ghi T ( 4 ) 0 1 0 Xoa t ( 4 ) 1 1 Bap benh loai ddng bo, hi£u theo nghla la viec ghi/xoa trong Flip-Flop chi co the xiy ra ddng bo vdi su xua't hien cua xung nhip C. Co hai loai J-K FF ddng bo : Loai dong bo theo su&n len (kf hieu d hinh 3-lb) va loai ddng bo theo suon xuong (hinh 3-lc) cua xung nhip. Su hoat ddng cua J-K FF co the tom tat d bang 3-2. Trong bang, ki h ieu t( l) bieu hien cho sudn len (hoac xudng) cua xung nhip ; ki hieu x y noi co the’ mang gia tri tuy y. Khi J = K = 1, Flop-Flop luon lat trang thai mdi khi co xung nhip di tdi, tira nhu ciu choi bap benh cua con tre. Vi du. Ve dd thi thdi gian cua tin hieu d diu ra Q cua J-K FF, theo dd thi thdi gian cua cac tin hieu dieu khie’n J, K va cua xung nhip C, cho trade d hinh 3-2. n n n p fl-ci j t>c K Hinh 3-2. Vi du minh hoa hoat ddng cCia J-K FF Ta ve cho hai trudng hop, ling vdi loai J-K FF ddng bo theo sudn len va loai ddng bo theo sudn xudng cua xung nhip C. Khi ve ta chi quan tam den tin hieu J, K d cac thdi die'm ling vdi sudn len (hoac xudng) cua xung nhip C, la nhirng thdi die’m Flip-Flop co the lat trang thai theo cac tin hieu didu khien. Trong khoang thdi gian giOa hai sudn len (hoac giua hai sudn xudng) cua cac xung nhip, Flip-Flop giu dn dinh. Bo qua thdi gian trd t^ cua Flip-Flop (xem muc 1-10-2, hinh 1-22) va coi d t = 0 thi Q = 0, ta co ket qua dang Q(t) ve duoc nhu d hinh 3-2. 3-1-3. D-Flip-Fop (D-FF) D-FF la loai Flip-Flop ddng bo vdi mdt diu vao dieu khien D. Tin hieu d dau vao dieu khien se truyen tdi diu ra Q (Q = D) mdi khi xuat hien xung nhip 69 C. Co ba loai D -F F d 6ng bo : loai d d n g bo th e o rnHec (k i h ieu d h in h 3 - Id ) ; lo ai d d n g bo th e o su&n len (h in h 3 -le ) va loai d d n g bo th e o su& n x u o n g (h in h 3 - If) cu a xung nhip. C ac b an g 3-3 va 3-4 tom tat hoat ddng cu a cac lo a i D -F F . B 6 n g 3 - 3 B 6 n g 3 - 4 L o ai d6ng bd th eo m iic L o i d 6ng bd th eo sucm x u n g c D Q t+ c D Q,^ 0 X O OX Q. 1 0° 1 0 - PX Q, 1 11 j T ( l ) 00 1 □ Of II t ( 4 ) 1 T “ V i du. V e d6 thi th d i g ian cua tin h ieu d dSu ra Q cu a D -F F , th e o d d thi thdi g ian cu a xung n h ip C va cu a tin h ieu didu k h iln D, ch o tru d c a h in h 3-3. O thdi d ilm ban d$u t = 0, tin h ieu 6 dciu ra Q = 0. n n n n . Q i. ■ , i i ' • , • ■ i • i i i i i * r 1----------------- ' 1 • 1 i i • • • ! . • ; ■ , • ' • , : : ■ • ' . . --------L_ _ i ' ' 1 1 • i i ■ i i 1 ■ ■ • i i < i i • i i 1 r 1 i ' • rt t t •ii t t Hinh 3-3. Vi du minh hoa hoat ddng cua cac D-FF 70 Ta ve d6 thi Q(t) ling vdi ba loai D-FF va co k£t qua nhu d hinh 3-3. 3-1-4. T-Flip-Flop (T-FF) T-FF la loai Flip-Flop co mdt diu vao didu khien T. M6i lin co xung tdi diu vao T, diu ra Q cua Flop-Flop se lit trang thai. Co hai loai T Flip-Flop : Loai tich cuc theo sudn len (kf hieu d hinh 3-lg) va loai tich cuc theo sudn xudng (kf hifiu d hinh 3-lh). 6 loai tich cuc theo sudn len, diu ra Q se lit trang thai tai thdi diem tag vdi sudn len cua xung T. d loai tich cuc theo sudn xudng, Q se lit trang thai tai thdi didm ling vdi sudn xudng cua xung T. n n n n n _Q Q >T Q ^ — <>T n Hinh 3-4. Vi du minh hoa hoat ddng cua cac T-FF Hinh 3-4 cho ta mdt vi du minh hoa hoat ddng cua hai loai T-FF. 3-1-5. Mot sd vi mach Flip-Flop. Hien nay ban phd bien tren thi trudng la hai loai vi mach Flip-Flop : J-K FF va D-FF. a) Trong mot "chip" J-K FF co tir 1 den 2 Flip-Flop cung loai, va chung thudng co cac dac diem cin luu y sau : • Trong Flip-Flop thudng co diu dal tritac (Pre) va diu xoa (CLR) khong ddng bo. Cac dau nay co thd la tich cuc tha'p hoac tich cuc cao. Nhu vay, ngoai J-K FF ddng bo, trong no con co mot S-R FF khong ddng bo. Diu S chinh la diu Pre va diu R chinh la diu CLR. Hien nay ri't hiem cac vi mach S-R FF khong ddng bo. Khi cin dung, ban nen tim cac "chip" J-K FF co cac diu dat trudc va xoa khdng ddng bo. 71 • D e cho viec sir du n g duoc linh h o at, m o t sd "chip" J-K F F co n h ieu dau vao J va K . Vf du IC 7 4 x x ll0 co ba d iu didu k h iln J j , J 2, J 3 va b a d iu d iek h iln K j, K 2, K 3. D iu dieu k h iln J, K cu a F lip -F lo p tu o n g u ng la J = J ,. J2. J 3 ; K = K ,.K 2 .K 3. ( 5 ) ^ (2) — (4) — (3) (1)CLR ( 11) ^ (14) — (12) (13) — : (15)^=< s O (13) S J — (6) (3) J 1 ---- >c n(4) J 2 ---- & J K 3 ( 7 ) (5) J 3 — c R (12) V 1*-) ---- >C Sj — (10)(10) K , — > C _ (11)K2 _ & K K 3 ( 9 ) (9) K 3 R (2 ) — R (8) (6) LJ U U U U U U CLR 74xx109 a) CLR 74xx70 b) c) Hinh 3-5. So do chan m6t so IC. J-K FF H in h 3-5a, b tuong irng la so d o c h an cu a cac "chip" J - K F F 7 4 x x l0 9 va 7 4 x x 7 0 . C hip 74109 co 16 ch an , vdi q u y udc sd thii tu cac c h an ta n g d in th eo ch ieu nguoc k im ddng hd (h in h 3 -5c). O h in h 3-5 a, b, cac sd tro n g da'u n g o ac d o n ch i sd thii tu chan tren vo. IC .7 4 x x 7 0 gdm 14 chan, cd m o t J-K F F vdi cac d iu vao d ie u k h ie n J p J 2, J 3 va K ,, K 2, K 3 . Kf hieu J 3 , K 3 la cac dau vao dieu k hien tfch cuc thap. T a cd : J = J j . J 2 . J 3 ; K - K j . K 2 . K 3 . V ay , J se bang 1 kh i J! = J 2 = 1 va J 3 = 0 ; cQng th e, K se b a n g 1 k h i K 2 = K j = 1 va K 3 = 0 . F lip -F lo p con cd hai dau vao d a t tru d c va xo a k h o n g d d n g bo tfch cuc tha'p (Pre va C LR ). N o cd vai trd n h u m o t S-R F F k h o n g d d n g bo, vdi s _ p re va R = C L R . T a cd the tdm tat hoat d o n g cu a "chip" 7 4 x x 7 0 tro n g b an g tran g th ai sau (b an g 3-5). 72 Bang 3-5 Pre/S CLR/R c J K Qr Chu thi'ch 0/1 1/0 X X X 1 1/0 0/1 X X X 0 S -R F F 1/0 1/0 X X X Q, 0/1 0/1 X X X Khong xac dinh 1/0 1/0 0 X X Q< 1/0 1/0 1 X X Q.J-K FF 1/0 1/0 t 0 0 Q.dong bo 1/0 1/0 t 1 0 1 theo sudn 1/0 1/0 t 0 1 0 len cua C. 1/0 1/0 t 1 1 Qt IC 74xxl09 (hinh 3-5a) co hai J-K FF vdi diu dat trudc va xoa khdng d6ng b6 tich cuc tha'p. Diu dieu khien K cung la tich cuc tha'p. Ban doc co the tu thanh lap bang trang thai md ta hoat ddng cua "chip" 74xxl09. D ■ f ( « > < 1 0 )P- S Q C =— (1 ) (1 2 ) — D C — (1 5 ) ( « ) - >C Q (1) >(9) -(8) R C — I (2: — Q' D3 - (1 4 ) <1 3 ) ^ C L R (3) (7) Qt q 2 Q — ( 6 Q2 (6) - (4)"[ (7) Da (1 0 ) ( 4 ) p ^ < Q C > = ■ (1 1 ) (3 ) — >C — C° O ) (2 ) -DQ D £ (8 ) <1> ^ ? ' ; C L R 74 XX7 5 74X X 7 4 - ( 5 ) (6) D ,— (12)(10 (11 (13)(1 5 (14 4 0 1 7 5 q 3 q3 q 4 04 Hinh 3 -6 . So d6 chan cua vai IC. D-FF b) Hinh 3-6 gidi thieu so do chan cua vai vi mach D-FF. M6i "chip" co tir 2 -M D-FF cung loai. Mdt sd D-FF cung co cac diu dat trudc va xoa khong ddng bo, vi du IC 74xx74 (hinh 3-6) gom hai D-FF vdi cac dau dat trudc va xoa khong ddng bo tich cuc tha'p. Vi mach 40175 (hinh 3-6) co bon D-FF ; chung co chung mdt diu ddng bo C va chung mot diu xoa tich cuc tha'p R . 73 3-1-6. Thanh lap T-Flip-Flop - Flip-Flop van n&ng • H ien nay tren thi trucmg kh d n g co cac vi m ach T -F F . M u 6n co T -F F ta p h ai thanh lap tir J-K FF hoac D -F F n h u a h in h 3-7a. Tir h o at d d n g c u a J-K F F va D -F F da trin h bay d trfen, ta de d an g n h an tha'y, n o i J-K I T h o ac D -F F n h u a h in h 3-7a se dugc T-FF. a) b) Hinh 3-7. Thanh lap T-FF tit J-K hoSc D-FF vd thdnh lap D-FF ti'J J-K FF • Ne'u dem noi J-K F F n h u d h in h 3-7 b se d u g c D -F F . T a tha'y J -K F F la lo a i F lip -F lo p va n n a n g , vi vdi nhurng cach n6'i k h ac n h au ta se d u g c cac loai F lip -F lo p khac. 3-2. 0NG DUNG CCA FLIP-FLOP C ac F lip -F lo p la nhung p h in tir lu u g iu 1 b it th o n g tin. C h u n g la nh u n g p h an tu co b an ca'u thanh cac m ach lo g ic d ay n h u b e d e m , th an h g h i d ic h ... C) day ta k h o n g de cap td i va'n d 6 nay va ch i x et vai ung d u n g p h 6 ca p k h ac cua F lip -F lo p . 1. T a th u d n g dung F lip-F lop lam phan tir lu u g iu tin h ie u d ie u k h ie n tro n g cac m ach dieu khien so. Vf du a hinh 3-8a, khi S = 1 logic = H va R = 0 logic = L th i Q = 1 lo g ic = H , k h o a tran sisto r d in bao hoa. Q u a cu o n d ay ro le co - d ien co d o n g , lam do n g m ach thap sang den D . K hi S = R = 0, n g h la la k h o n g co n tin 74 hieu didu khien dong, diu ra Q ciia S-R FF van duy tri muc cao H va mach chie'u sang den van dong. Mufi'n ngat mach, ta dua tdi cua vao Flip-Flop tin hieu ngat S = 0, R = 1, diu ra Q se lat xutfng mire tha'p L lam transistor khoi. c) Hinh 3-8. Mdt so ting dung ciia S-R Flip-Flop. 2. Co the dung S-R FF de loai trU anh huang cua hien tuong "nay" cua khoa ca khi khi dong/cit. Khi dung khoa chuyen mach co khi de thay doi mik logic cua mfit bien thucmg lam xui't hien mot chu6i xung khong mong muon, do cac dao d6ng co cua tie'p di£m giy ra. Tren hinh 3-8b, khi ta thay d6i vi tri khoa K de bien logic Q chuyen tir miic cao H xudng miic tha'p L hay nguoc la i; trong thcri gian qua do, a diu Q se xuit hien cac xung khong mong muon do su rung dcing cua tiep diem khi chuyen mach. Sir dung S-R FF loai diu vio ti'ch cuc tha'p n6’i nhu hinh 3-8c, se loai bo duoc anh huong ciia cac dao dOng co cua khoa K khi chuyen mach ddi vdi tin 75 hieu lo g ic a d iu ra Q. Cd th i thanh lap S-R FT lo ai dau vao tfch cu c th a p tir m ach g6m h ai p h in tijr N A N D hai d iu vao. D iu ra cu a p h an tir nay d u o c nd i vdi m ot d iu vao cua p h in tu kia . H ai d iu vao co n lai n h an tin h ieu d ilu k h ien S, R. 3. N gudi ta co n hay du n g T R ip -F lo p d l th u c h ien viec c h ia d o i ti n s6 ciia m d t day xung vudng goc. T u hoat dong cu a T F lip -F lo p (m uc 3 -1 -4 . h in h 3-4), n h an tha'y : N lu du a tdi d iu vao T ciia F lip -F lo p m d t d ay x u n g v u d n g lap lai, tin sd f, ta se n h an dugc d hai d iu ra Q va Q hai day xu n g vu d n g go c n g u g c pha nh au , ti n sd f/2 (h in h 3-9a). © _ r - >T a) c) Hinh 3-9. Dung Flip-Flop de chia ddi tan so va tao mach phat xung don 4. N udi ta cd the du n g D -F F h o ac J-K FT , lo ai cd dau vao d a t tru d c S va d iu vao xoa R kh d n g d 6ng bo (v i du IC h o C M O S H E F 4 0 1 3 B cd h a i D -F F , IC H E F 4027B gdm hai J-K FT) de tao th an h m a c h p h at x u n g dem (m ach d a hai d a n on). H in h 3-9b, c tu o n g irng la so d d m a c h p h a t xu n g d o n d u n g D -IT va d u n g J-K F F , vdi R 2 » R ,. X et m ach hinh 3-9b. O tran g th a i tin h , kh i k h d n g cd x u n g ki'ch thi'ch d u a tdi dau vao don g bo C ciia D -F F , dau ra Q nam on d in h 6 m ire th a p L ~ OV. D at ki'ch thi'ch la m o t budc nhay d u o n g vao dau C, ta cd Q = D = m ire ca o H = d ien a p n g u d n cu n g ca'p d at co d in h o dau D. Tu C d u g c n ap d ie n tir m u c d ie n ap cao H d Q q u a cac d ie n trd R j, R 2- D ien ap tren tu tan g d an , phu th u o c h an g so th o i g ian n ap t n a R 2C (bo qu a Ri vi R j « R 2). K hi d ie n ap tren tu d a t g ia tri m a d iu xoa k h d n g don g bo R yeu cau, dau ra Q q u ay trd lai m u c th a p dn d in h L. Tu C p h o n g d ien q u a d io d va d ien trd R „ vdi h an g so th d i g ia n p h o n g xp a R ,C . 76 v a y . vdi mot ki'ch thi'ch a dau vao C. mach cho d hai dau ra Q va Q hai xung dan nguac nhau va co do rong : ts *0.7R ;C (3-1) Di6n tra R, nhim han che su phong qua nhanh cua tu C vdi dong phong lorn. Thucmg R) chon khoang vai kn tra xuong. Hoat dong cua mach hinh 3-9c tuang tu nhu da trinh bay a tren. 3-3. MACH PHAT XUNG DON (MACH DA HAl DON 6n) DONG NANR/NOR Mot cach don gian va re de tao thanh mach da hai dan on la dung cac phin ttt NAND hoac NOR trong cac 1C ho CMOS, vi du 1C 4001 (g6m 4 phin tii NOR hai diu vao) hay 1C 4011 (gom 4 phin tir NAND hai diu vao). Hinh 3-10a, b tuang ling la cac mach da hai dan 6n dung NOR va NAND. Xet mach hinh 3-10a, trong do phin tu NOR so 2 duoc nd'i thanh phin tir DAO ; uv la dien ap ki'ch thi'ch a diu vao. ur la dien ap ra. Khi khdng co xung kfch thi'ch a diu vao, ur d miic tha'p L * OV vi dat vao phan tir DAO so 2 la miic cao H ~ +U. Dau ra A ciia phan tir NOR so 1 cung a miic cao H vi ca hai dau vao cua no deu d miic tha'p L = OV. Tu C khong tich dien vi ca hai cuc ban deu a miic cao H. Vay trang thai dn dinh ciia mach la miic tha'p L ~ OV d diu ra (ur = L = OV). Khi dat mot xung ki'ch thi'ch duang a dau vao uv, dau ra A cua phan tir so 1 se chuyen ngay xuong miic tha'p L va truyen qua cuc ban phia phai cua tu C. Vi v|y, dien ap ur a diu ra phin tir DAO so 2 nhav len miic cao ; No duac din tra ve mot diu vao cua phin tir NOR sd 1, do do dau ra A ciia phin tir vin duoc duy tri d miic tha'p L mac du khong con ton tai xung ki'ch thi'ch u». Mach chi nim a trang thai khong dn dinh vai ur = H trong mot thai khoang xac dinh. That vay, khi ur chuydn len muc cao H, ling vdi thcri diSm dat xung ki'ch thi'ch. cung la luc tu C duoc nap tir nguon cung cap +U qua R| ; Dien ap phia cuc + (cuc ban phi'a phai) cua tu tang din theo luat ham mu tdi khi dat gia tri nguang lat UT * + y thi phan tir DAO so 2 lat xudng miic tha'p vdi ur = L = OV. Ta thay. cii mdi lin co xung ki'ch thi'ch uv thi mach lai cho mot xung vudng goc ur d diu ra, do rong xung tx ti'nh gan dung bing : tx * R,Cln2 * OJ.Rj.C (3-2) 77 Hinh 3-10. Mach da hai don Sn dung NOR/NAND M ach da hai dcrn on a H -3-10b co nguyen If lam viec gidng m ach hinh 3 -10a. C ac m ach da hai du n g N A N D /N O R a tre n k h d n g thfch h a p vdi n h u n g ling du n g yeu cSu dd ch in h xac cao, vi dd rd n g x u n g tx phu th u d c dien ap n g u 6n cu n g ca'p +U va phu th u d c kh a n h ilu vao ban th an cac IC d u a c sir d u n g . T u C c6 th i co gia tri k h oang tir lOOpF den vai n g h in |xF, dien tr a R , n a m tro n g k h o an g vai k Q den vai M Q . 3-4. MACH DA HAl PHl£M 0|NH DCJNG CAC IC S6 N g u d i ta con hay dung cac p h in tu N A N D /N O R h o C M O S (vf d u c ic IC 4 0 1 1 , 4 0 0 1 ) d i tao th an h n h u n g m ach da h ai p h ilm d in h , p h a t ra d ay x u n g lap vudng goc vdi d d chfnh xac kh d n g cao. T a ch ia cac m a c h n ay th a n h h a i n h o m : C ac m ach k h d n g d ilu k h iln va cac m ach co d ilu k h iln . 3-4-1. Mach da hai phiem dinh khong dieu khien la m a c h lien tu c p h at ra day xun g vudng gdc vdi chu ky lap x ac d in h , k h d n g c6 su d ilu k h iln g id i han k h o an g th d i gian p h at xung. H in h 3-1 la la so d 6 c a ban cu a m a ch , g 6m hai p h in tu D A O nd'i tin g va m ach d in h thcri R -C . C ic p h in tir D A O tro n g s a d 6 th u d n g do p h in tu N A N D /N O R ho C M O S tao th a n h (x em m u c 1-7-2). Hinh 3-11. Mach da hai phiem dinh khdng dieu khien 78 Xet su lam viec cua mach hinh 3-1 la. Gia su d thdi diem bat diu khao sat, u, d miic cao H * +U = dien ap ngu6n cung ci'p, di£m A d miic tha'p L » OV va diem B d miic cao H ; Tu C khtfng tfch dien va duoc nap theo chi£u til ur = H -» C -» R -> A. Dien ap d di&n B se giam din tit mire cao H theo su giam cua dong nap cho tu. Khi diiim B dat gia tri nguang lat UT ~ H/2 « +U/2, thi phin tir DAO stf 1 lit trang thai va di£m A nhay len miic cao H, dien ap ra Ur tut xuong miic tha'p L » OV. Tu C luc do cung nhanh chong phong dien qua mach a cua vao cua phin tu 1. Dien ap 6 di£m B vi vay cung tut ngay xufl'ng miic tha'p L. Tu C tra nen khdng tich dien va bat diu duoc nap theo chi6u nguoc lai, tir A = H -> R -» C -» ur = L. Dien ap a diem B vi vay tang din tir miic tha'p L theo su tang ciia dien ap tren tu. Khi B dat nguong lat UT thi phin tu DAO stf 1 lai lit trang thai va diem A lai chuyen tir H sang L, ur nhay tir L len H. Tu C mdt lin nua nhanh chong phong het dien qua mach vao cua phin tu 1 va B = H. Tu lai bat diu dugc nap theo chilu tirur = H - » C - > R - > A = L. Qua trinh tie'p tuc lap lai nhu tren. Ke't qua mach cho ta dien ap ra u, la mdt day xung vuong goc doi xiing vdi chu ki lap : T * 1,4RC (3-3) va bi^n dd xip xi dien ap ngudn cung ca'p +U. Ne'u chon tu C tir vai nF de'n vai HF (khdng dung tu hoa) va dien tra R trong dai tir vai kQ de'n hang chuc MQ, tin stf cua day xung ra co th6 nim trong dai tir vai Hz de'n khoang 1MHz. Dien ap ngufin cung ca'p cho IC ho CMOS co th^ lay tir 3 h- 18V. Nhugc di^m cua mach hinh 3-1 la la day xung vu6ng goc nhan dugc khfing hoan toan d6'i xung ; Tin stf cua day xung thay d(Si theo dien ap ngu6n cung ci'p va theo cac "chip" IC khac nhau dugc su dung. Khi dien ap ngu6n cung ci'p ting 10% thi tin sd' day xung phat ra giam khoang 0,8%. D^ giam de'n t6'i da cac nhugc die’m cua mach hinh 3-1 la, a ducmg cua vio ciia phin tir stf 1, ngugi ta dit them dien tra R| (tren sa dtf hinh 3-1 la c6 ve dien tra Ri a ben canh vdi net dirt khiic, y noi c6 thi chen them vao). Tri stf cua Rj chon ra't ldn han R, (vi du chon R| = 10R). Mach da hai phie'm dinh hai ting c hinh 3-1 la con co mtft nhugc dilm quan trong la sudn len va xutfng cua cac xung khtfng tran, t6n tai cac gai xung nhieu 6 hai sudn xung. De loai bo nhugc dilm nay, ta dung mach da hai phiem dinh ba ting d hinh 3-1 lb. Dien ap ra ur ciia mach la mdt day xung vudng goc dtfi xiing. khdng co gai xung nhieu d hai sudn xung. Hoat dtfng cua mach nhu sau : Gia sir d thdi diem ban diu khao sat, dien ap ra ur d miic tha'p L * OV va tu C khdng tich dien, diem M va N co dien ap nim d miic cao H * +U, (+U la dien 79 ap nguon cung ca'p), dien ap die’m P la d m iic tha'p L. Tu C b at d iu d u o c nap theo chidu tir M = mire cao H —> C —» N —> R —» u r = L . D ien a p 6 d ie m N giam dan tir mire cao H theo sir giam cua don g nap. K hi d ien ap d iem N giam tdi gia tri ngudng lat UT, thi phan tu D A O sd 1 lat trang thai va dau ra P cu a no chuye'n ngay len m iic cao H, con d iu M lat sang m iic th ap L va ur n h ay len mure cao H. Tu C nhanh chong phong dien het qu a ciia vao cu a p h in tir so 1 va die’m N cung chuyen ngay xuong m uc tha'p L. Bay gid, tu C lai bat d iu n ap th e o chidu n guoc lai, t i r u r = H —» R —» C —» M = L. D ien ap d d iem N tan g dan tir m trc th ap L a OV, cho tdi khi dat n gudng lat U T thi phan tii 1 lai lat tran g th ai, d iem P chu y en xuong mtrc tha'p L va die’m M nhay len m iic cao h in h D ien ap ra ur c h u y ln nhanh xuong m iic tha'p L. Tu C m au chong phong het d ien q u a cira vao cu a p h in tii sd 1 va N cung d m iic cao H. Q ua trinh tie'p d ien lap lai n h u d a trin h bay d tren. Ke't qu a u r la m ot day xung vuong goc ddi xiing k h d n g cd gai x u n g n h ieu d hai sudn xung. 3-4-2. Mach da hai phiem dinh co di£u khien N o la m ach chi cd the phat ra day xung vuong goc tro n g m o t th d i khoang x ac d in h m a ta co the d ieu khien dugc. D e co loai m ach n ay , ta dung m ach da hai phie'm d in h kh d n g d ieu kh ien d hinh 3-11, vdi day xu n g ra ur d u g c d in tdi m 6t cd n g V A hay H O A C (x em m uc 1-8-1). D ung m o t x u n g cd d o ro n g tx de didu k h iln m d cdng cho day xung u r di qua. Sau thdi g ian tx thi c d n g d o n g va day xung bi chan. T uy nhien, tir tfnh chat la cac p h in tii N A N D /N O R cu n g cd the sir dung nhu m dt cdng logic, ta cd the th an h lap cac m ach da hai phie'm d in h hai tin g co didu k hien n h u o h in h 3-12, trong dd dk la tin hieu d ieu k h ien de m ach lam viec, u r la day xung ra.