sổ tay cdt chuong 40-tke hthg logic

8/6/2019 s tay cdt Chuong 40-Tke Hthg Logic

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40Thit k h thng logic

M. K. RamasubramanianNorth Carolina State University

40.1 Gii thiu logic s ................................ ......... .....1

40.2 Thit b bn dn .............................................. ....2

40.3 Cc cng logic ............................................. .......4

40.4 Thit k logic ..................................................... .5

40.5 Ti thiu ho .......................................................5

40.6 Cng ngh cng Logic ........................................8

40.7 Mch tch hp cng Logic ................................11

40.8 Thit b Logic kh trnh (PLD) .........................12

40.9 V d p dng C in t ................ ......... ........12

40.1 Gii thiu logic s

Trong in t tng t, in p v dng in bin thin lin tc t gi tr thp nht n gi tr cao nht cho php. Nhngbin s ny c o c, khuych i, thm vo v bt i thng qua cc mch tng t c c kt qu mong mun. Vd, khi o nhit s dng cp nhit , th cn phi khuych i in p n mt di o ph hp, xc nh mc in ptng ng vi nhit o c, v kt qu u ra trn vn k s biu th nhit . Trong thit k ny th cn phi tr i mt

in p offset b tr, ri nhn vi mt h s khuch i ph thuc vo di nhit . in p v dng in c th ckhuych i nh cc b khuych i thut ton v tranzito. Nhit o c c th l tn hiu phn hi trong vng iukhin kn ca mt h C in t iu khin nhit . Trong in t s, cc bin c biu th di dng nh phn nhn gi tr0 hoc 1. Trong v d ni trn, chng ta cn phi ng van slnit li nu nhit xung di mt gi tr xc nh v mvan nu nhit vt trn gi tr ngng. Trong trng hp ny, n gin chng ta ch cn nhp cu tr li NG hoc SAIi vi cu hi nhit ang trn hay di ngng? Chng ny s trnh by s biu din ca cc dng bin dng nhphn trong mch v cc thao tc vn hnh bng tay t c nhng kt qu mong mun.

Cc cp chuyn i Logic

Trong cc mch s, mc in p biu th cc trng thi nh phn, trng thi CAO hoc NG c biu din bnggi tr in p ti a, thng thng l 5V, v trng thi THP hoc SAI c biu din bng gi tr in p ti thiu thngthng l 0V. Trong logic Boolean,1 biu th NG v 0 biu th SAI . Trn thc t, bt k mc in p no trn mc

u vo ti thiu, VIH, th c coi l logic CAO v bt k mc in p no di mc u vo ti a, V IL th c coi l logicTHP. u ra ti thiu t mt thit b logic mc logic CAO c biu th bi V OH (khc vi VIH), v u ra ti a mclogic THP c biu th bi VOL (khc vi VIH). Nhng gi tr ny ph thuc vo loi thit b logic, th biu din gi trca nhng thng s ny c th hin trong hnh 40.1 [1].

VCC l in p cung cp. Khong gia VOH v VIH, hoc gia VOL v VIL, c gi l gii hn nhiu. iu quan trng lphi thit k mch logic sao cho in p khng bao gi ri vo vng gia V IH v VIL. Phm vi ny c gi l vng cm m thit b logic khng c kh nng nhn dng tn hiu. S chnh gia mc chuyn ca cc cng ngh khc nhau nh logic5V, logic 3.3V, CMOS (cht bn dn oxit - kim loi tng hp ), v TTL (logic tranzito-transistor) cn phi c cn nhckhi ghp nhng h thng ny vi nhau.

Mt bin logic c th thay i cc trng thi nhanh c biu din bi mt chui xung l tng nh hnh 40.2. Cc binc th dao ng gia 0 v 1 theo chu k hoc khng theo chu k. Cc cng logic nhn cc tn hiu ny lm u vo, thc hincc php tnh Boolean gia chng v a ra u ra chnh xc vi mt tc tnh ton mong mun. Thit k hon chnh,, sdng cc hm logic v ng dng chng trong cc mch l mt phn khng th thiu trong thit k h C in t.

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S tay C in t

HNH 40.1 Mc chuyn mch ca cc cng logic [1]

HNH 40.2 Cc mc logic tn hiu chu k v khng chu k

ng dng cng Logic

Hy xem xt v d v mt con robot t ng di chuyn trn b mt mt chic bn. Con robot phi di chuyn v pha chc nh du bi mt ngun nh sng v phi trnh cc chng ngi vt cng nh khng c ng ra khi bn. Gi nhrng chng ta c ba cm bin s l cm bin pht hin chng ngi vt, cm bin pht hin ranh gii v cm bin pht hinch, th chng ta c th vit c mt hm logic n gin biu th s di chuyn v pha trc, nh thy phng trnh(40.1). Tt nhin, y khng phi l mt hm logic hon thin gip robot di chuyn hp l. Tuy nhin, y chng ta ch tptrung vo mt kha cnh ca vn l minh ho cho tnh ng dng ca cc hm.

DI CHUYN LN PHA TRC = (KHNG PHT HIN CHNG NGI VT)

AND (KHNG PHT HIN RANH GII)

AND (NHN THY N BO HIU) (40.1)

Ba cm bin ny c ni vi cc u vo ca mt mch logic bao gm cc cng logic, trong v d ny l mt cng ANDba u vo v u ra s iu khin ng c. Tt nhin, cc trng hp khc v cc ng thi ca robot khi pht hin ranh giihoc chng ngi vt, hoc khi khng c n hiu cn phi c xem xt lm cho mch ny tr nn hon chnh v huch. Hnh 40.3 l s thc hin cc lnh logic c m t trong phng trnh (40.1).

HNH 40.3 S hm logic iu khin di chuyn ln pha trc ca mt robot trn bn

40.2 Thit b bn dn

it

hiu c cc cng logic, iu quan trng l phi nm bt c mt cch c bn nht v cc thit b bn dn, c bitl it v tranzito. it l mt lp tip gip pn, tc l it c to thnh bi mt lp vt liu dng p (thiu cc electron) vmt lp vt liu dng n (nhiu cc electron) c ghp li vi nhau. Khi cc dng ca pin c ni vi mt p ca it (ccdng - ant), v cc m ni vi mt n ca it (cc m catt) th it phn cc thun khi in p xuyn qua lp tip gipphi vt mc 0,7 V. Khi o cc cc li, it phn cc ngc v khng dn in cho ti khi xut hin mc in p rt caoxuyn qua lp tip gip, mc in p ny c gi l in p nh thng. Trong thc tin, chng ta c th gi thit rng mt

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Thit k h thng logicit phn cc ngc th khng dn in. S , k hiu v mch phn cc thun ca it c th hin trong hnh 40.4. Khiphn cc thun, it c th c coi nh mt kha chuyn mch ng n gin vi mc in p ri trn n l 0,7 V v khiit phn cc ngc th n ng vai tr nh mt kha chuyn mch m.

Tranzito lng cc

Mt tranzito lng cc c ba lp bn dn. Trong mt tranzito npn, Mt lp p rt mng c kp ga hai lp n. Cc loitranzito v k hiu ca chng c th hin trong hnh 40.5(a,b).

HNH 40.4 it v cc trng thi ca n

HNH 40.5 (a) K hiu tranzito npn, (b) k hiu tranzito pnp

HNH 40.6S biu din nguyn l hot ng ca tranzito npnMt tranzito c 3 cc l cc gp (C), cc pht (E), v cc gc (B). i vi mt tranzito npn nh trong mch hnh 40.6,

lp tip gip cc gc-cc pht phn cc thun, tranzito ny s dn in nu in p V BE vt qu in p phn cc thun vilin kt pn, thng thng l 0,7 V. VBE s tng ln bng cch tng in p B. Tuy nhin, lp tip gip cc gc-cc gp sphn cc ngc khi cc gp C c in th cao hn. Khi dng in chy trong vng cc gc-cc pht, cc electron t cc phts di chuyn sang cc gc bng cch lp y cc l trng ca lp p v sau s gii phng cc electron ca lp p ra khicc gc. Tuy nhin, do s lng cc l trng trong lp p (rt mng) c hn, nn cc electron di chuyn khi cc pht s cin th trong ng dn cc gp-cc pht ln hn v s nhy khi lp tip gip. Kt qu l to ra mt dng in ln, I C,chy trong vng cc gp-cc pht. Do , tranzito l mt b khuych i dng in. Mt dng in nh chy trong vng ccgc-cc pht, IB, c khuych i vi mt h s khong 100 trong ng dn cc gc-cc pht. Khi dng in trong vngcc gc-cc pht c tng ln bng cch tng VBE, th dng in cc gp-cc pht tng ln bng cch gim VCE. Do cc gpc ni vi ngun in, VCC, v cc pht c ni vi t, nn tranzito iu khin dng in ny bng cch kim sot s stgim in p trn lp tip gip cc gp-cc pht, v tip tc gim in p khi dng in cc gc-cc pht tng ln. R rngl in p khng th gim xung di 0V; trn thc t n khng th gim xung di mc 0,2-0,35V. Trong nhng trnghp nh vy, tranzito c coi l b bo ho v ng vai tr nh mt kho ng. Cc mch cha tranzito trng thi bo hoc gi l mch bo ho; v d nh cc cng logic h TTL. Cc mch khng cho php cc tranzito trng thi bo ho vtm c mt im hot ng n nh trong vng tch cc ca tranzito c gi l cc mch khng bo ho, v d nh cc

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S tay C in tcng logic 2 cc pht (ELC emitter-coupled logic). u im ln nht ca mch khng bo ho l ch so vi mch bo hotrng thi c th c thay i cng vi tc .

HNH 40.7 Cc k hiu MOSFET dng knh n v p

Tranzito hiu ng trng (FET)

Nhng thit b ny c ch to d dng hn v tiu tn t silicon hn. C hai loi FET l FET dng tip gip (JFET) vFET bn dn oxit kim loi (MOSFET). Trong c hai loi ny, dng in ra s c iu khin bi mt in p u vo nh,

gn nh khng c dng in vo. Ba cc c gi l cc ngun (S), cc mng (D), v cc cng (G). Hnh 40.7 l cc k hiuca MOSFET dng knh n v p m rng. MOSFET l mt loi tranzito ph bin nht.. Cng MOSFET khng tip xc invi cc ngun v cc mng. Lp silicon-ixit ng vai tr cch ly cng ny. in p cng s ht cc electron vo vngdi ca cng v cung cp knh dng n trong cht nn dng p dn in gia cc mng v cc ngun. y c gi ldng m rng ca MOSFET.

Loi th hai l dng nng cp-tho rt, c s xut hin ca knh n gia cc mng v cc ngun, tuy nhin in trknh c th c tng ln hoc gim i bng cch cp in p m hoc dng tng ng cho cng. Cc chc nng v k hiuca MOSFET nng cp-tho rt c m t trong hnh 40.8. MOSFET c tc chm hn cc thit b lng cc nn cdng trong cc mch tc thp nhng c s dng nhiu do d ch to v tiu tn t silicon.

HNH 40.8 MOSFET dng nng cp - tho rt

40.3 Cc cng logic

Cc cng logic l cc khi c bn trong mch logic v my tnh. Cc h C in t c mt khi tnh ton trung tm thchin cc hm logic c trng trong phn cng. Mt mch logic gm mt vi cng logic cng hot ng. Chng ta s bn v

cc cng logic ni chung v cc khi ca h C in t nh. Cc php ton logic c th c phn thnh hai loi l logic thp v logic dy. Trong trng hp mch logic t hp, kt qu u ra ca cc cng logic ch da trn gi tr tc thi ca ccu vo, cn mch logic dy, s thay i ca u ra ph thuc vo trng thi hin ti cng nh trng thi trc khi c sthay i gi tr ca u vo, do n c thuc tnh nh. Hn na, cc mch logic dy c th ng b hoc khng ng b.Khi u ra thay i mt cch ng nht vi u vo ng h th n c coi l ng b. Khi cc u vo c c ngay khimch c bt k thay i no, th mch ny c gi l mch logic khng ng b. C ba php ton c bn l hm AND, OR,v NOT. Cc php ton logic khc l cc php ton bt ngun t cc php ton c bn. K hiu cng AND v bng chn lca n c th hin trong hnh 40.9. Cng AND c th c hn hai u vo.

Hnh 40.10 biu th cng OR. y, u ra c gi tr CAO (HIGH) khi mt trong hai u vo hoc c hai u vo CAO.Cng OR cng c th c nhiu hn hai u vo. Hnh 40.11 l mt cng o, hay cn gi l cng NOT. Loi cng ny ogi tr nhn c u vo, v d u vo CAO c chuyn thnh u ra THP v ngc li.

Cc cng logic ph bin khc bt ngun t nhng php ton c bn ny l NAND, NOR, v cng Exclusive OR. CngNAND l s kt hp ca cng AND v cng NOT; NOR l s kt hp ca cng OR v cng NOT, v Exclusive OR c thc to thnh nh s kt hp ca cng OR, NAND, v AND.

T hnh 40.12 n hnh 40.14 chcho chng ta thy cc dng cng phi sinh l NAND, NOR, v XOR cng nh cc bngchn l tng ng ca chng. Phn cng s dng cc dng cng ny v cc hm logic l cc khi c bn ca mt my tnhs.

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Thit k h thng logic

40.4 Thit k logic

Trong bt k thit k no, iu quan trng l phi lm cho sn phm tr nn n gin, c tnh nng mnh v mang li hiuqu kinh t. Thit k h C in t v mch logic cng khng l trng hp ngoi l. Khi mt hm logic ca mt h thngc th hin di dng cc mi quan h gia cc u vo v u ra, th chng ta s khng bit chc c rng liu s lngcc nhn t tham gia vic thit k c ti thiu khng hay liu chng ta c th n gin ho thit k hn na khng. Nu phc tp c xc nh bng s lng cc cng logic c s dng, th vn t ra y l cn phi gim thiu cc hmlogic v mt ton hc. Tuy nhin, nu phc tp c xc nh bng s lng cc ICs c s dng trong mch (din tchchim trong mch) th cn phi cn nhc thm, chng hn nh cn phi s dng cc dng cng cng loi cng nhiu cng tt,mc d n c th khng ti thiu nu xt v s lng cng. Vic ny c u tin hn vic gim bt cc dng cng khcnhau, do nu s dng nhiu dng cng i hi phi c nhiu IC hn, m i khi li khng s dng ht s cng.

40.5 Ti thiu ho

Mt phng php ti thiu ho cc hm Boolean l dng bng Karnaugh (bng K). T nhng m t chc nng ca biton t ra, thit lp c cc lnh logic dng cho vic iu khin robot trn bn nh phng trnh (40.1). Bng chn l thhin mi quan h gia cc u vo v cc u ra. Chng ta lp c bng chn l vi thit k dng ba bin s, nh hnh40.15.

Hm logic c th c vit nh sau:

X = ABC +ABC+ABC+ ABC (40.2)

Nu thit k mch thc hin hm logic trn m cha cn nhc n cc yu cu khc th cn phi c bn cng AND 3u vo, 1 cng OR 4 u vo v 3 cng o. Nu gi thit rng c th s dng c hai dng b v khng b ca tn hiu ngvi mi bin, chng ta s thit k mt mch t hp hai tng thc hin mc ch . Nu s dng bng Karnaugh, chng tac th ti thiu hm Boolean, n gin ha dng v s lng ca cc cng logic cn thit m vn m bo thc hin ngchc nng ca mch logic.

Hnh 40.9 K hiu v tc ng ca cng AND

Hnh 40.10 K hiu v tc ng ca cng OR

Hnh 40.11 K hiu v tc ng ca cng o hay cng NOT

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S tay C in t

Hnh 40.12 K hiu v tc ng ca cng NAND

Hnh 40.13 K hiu v tc ng ca cng NOR

Hnh 40.14 K hiu v tc ng ca cng XOR

Hnh 40.15 Bng chn l dng cho thit k v ti thiu ha mch logic

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Thit k h thng logic

Hnh 40.16 Bng Karnaugh dng cho thit k mch logic c 3 u vo v mt u ra

Bng Karnaugh c xy dng da trn bng chn l trong hnh 40.15. Hai bin AB c gn cho cc ct v bin th 3c gn cho hng. Cc gi tr c sp xp sao cho cc gi tr trn ct v hng lin k ch khc nhau 1 bit.

Hnh 40.16 thc cht l cc hm logic tng ng c m t trong bng chn l trong hnh 40.15. Do cc lin ktrong bng K ch khc nhau 1 bt nn s thay i bit l khng quan trng trong mt nhm cc lin k. ti thiu ha hmlogic, xc nh cc nhm lin k nhau trong bng K v trong mi nhm mt bin khng c vai tr quan trng i vi gitr u ra X. Bin s c gim thiu v qu trnh ny c tip tc cho n khi tt c cc nhm c xc nh sao cho mimt phi thuc t nht mt nhm cng hng hoc cng ct. Cui cng, kt hp cc nhm xc nh nh hm OR, ta s thuc hm ti thiu.

Hnh 40.17 Mt xung thc vi cc thng s c trng[2] Hnh 40.18 Tr lan truyn

Hnh 40.16 gm 3 nhm lin k nhau theo hng v ct c xc nh bi vng trn bao quanhchng :

Nhm 1. Ch mt bin B l bin i trng thi, do n c th c gim thiu v dng ti thiu cho nhm lAC.

Nhm 2. Ch mt bin A l bin i trng thi, do n c th c gim thiu v dng ti thiu cho nhm lBC.

Nhm 3. Ch mt bin C l bin i trng thi, do n c th c gim thiu v dng ti thiu cho nhm lAB.

Do dng ti thiu cho hm logic l: X = AC + BC + AB

Hm ny c th c thc hin vi mt IC cng AND 2 u vo v mt cng 3 u vo OR. Phng php bng K gip gim thiu ti 6 bin.

Cc c tnh ng hc

Bng vic nghin cu hm logic v ti thiu ha chng, chng ta c th xy dng c mch logic. Tuy nhin m bomch hot ng c nh mong mun th cn cn nhc k cng cc c im ng hc ca mch logic. Nh ni trn, tnhiu u vo c th thay i nhanh trong mt h thng v mch logic cn hot ng nh mong mun tn s vn hnh cah thng . S hot ng chnh xc ca mch logic khi cc u vo thay i nhanh l mt cn nhc quan trng trong thit k.Nh trnh by trn, chng ta gi thit rng tn hiu logic l mt xung vung l tng v cc cng logic khng c tr.Chng ta hy kim tra tc ng cu 2 gi nh ny bng cch xem xt k cc ng x ng hc ca mch logic. Mt dngxung thc c th hin trong hnh 40.17 [2]. Thi gian tng (rise time) c k hiu l tr v thi gian st(fall time) c khiu l tf. Ngoi ra, xung cn c thi gian n nh, overshoot v undershoot khi thay i trng thi. Bin tn hiu l hiugia hai mc n nh ca tn hiu l mc cao (VH) v mc thp (VL), v d t 100% n 0% v t w l b rng xung ca tnhiu c tnh mc 50% bin . tTHL, tTLH ln lt l khong thi gian chuyn i t cao xung thp v t thp ln caoca tn hiu u ra. tPHL v tPLH ln lt l thi gian tr khi chuyn i trng thi t cao xung thp v t thp ln cao. Vi tc hot ng trung bnh, tPHL v tPLH thng ph bin mc 30 ns. Khi mt u vo ca cng logic thay i trng thi u ra

s b tr sau bi thi gian tr c trng c gi l thi gian truyn dn, n c o bng hiu thi gian tnh t im tngng mc 50% ca bin u vo n50% ca bin u ra. M hnh n gin ho xung thc ca mt b nghch oc th hin hnh 40.18.

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S tay C in t

[3]. Cc gi tr truyn dn thng thng c tnh theo nano giy, c thc thy trong bng d liu ca mt thit b. i vi mch logic vic phn tch thi gian tr c thc hin bng cch tnhtng thi gian tr t u vo n u ra khi u vo thay i trng thi v xc nh bt k vn tnh (tn s c lp) v ccvn ng hc. Khi thm cc cng vo mch c th s ny sinh nhng vn khc.

Cc cn nhc khc khi thit k

S lng cng logic ca mt cng cho trc c th iu khin c gi l fan-outv s lng cng c th ni n uvo ca cng c gi l fan-in. Nhng s liu c cho bi bng s liu cn c tn trng. Hn na, ti thiu s lngcc IC cn thit trong mch logic l cn nhc rt quan trng d c th yu cu phi sa cha thit k v phi dng nhiu cngcng loi hn so vi kt qu ti thiu ha bng K. S dng cc cng cng dng tch hp cc IC cng l mt im cn cnnhc khi thit k mch logic.

40.6 Cng ngh cng LogicH logic u tin c thng mi ha l loi logic in tr-tranzito (RTL), trong transistor c s dng trong mch

l cc chuyn mch tc cao. Tip theo l logic it-tranzito (DTL) v logic tranzito-tranzito (TTL) c pht trin. Khim loi RTL v DTL li thi th loi TTL c s dng rng ri. C nhiu loi logic TTL , c th l: tc cao (H), tc thp (L), Shottkey (S) v Shottkey cng sut thp (LS). Cng CMOS logic l s b sung hon thin cng logic trn c scng ngh thit b bn dn xitt-kim loi (CMOS). Nhng thit b ny yu cu cng sut thp v ci thin c c tnhnhiu. Nhng thit b ny c nhy tnh cao v do d b h hi hn. S kt hp ca CMOS vi phng php lng cccho ra kt qu l cng ngh BiCMOS, s dng cc thnh phn CMOS bn trong v cc u ra lng cc cng sut ln. Cnhiu h BiCMOS khc nhau pht trin tdng BiCMOS ban u [1].

Logic in tr-tranzito (RTL)

Hnh 40.19(a) gii thiu mt cng RTL o v hnh. 40.19(b) gii thiu cng NAND. Transistor c gi thit l hotng ch bo ha. Do ch bo ha bnh thng, c mt in p rt nh tn hao trn lp tip gip cc gp-cc phtv do yu cu dng in rt nh trong vng cc gc-cc pht transistor bo ho. Trong hnh 40.19(a), in p u ranm trong khong 0.3-5.0 V. i vi cng NAND c m t trong hnh, mc logic thp ca u ra l 0.6 V tng ng vi st gim trn cc thu-cc pht ca 2 tranzito ni tip. Nu thm s transistor thm u vo, nng lng tn hao s tngln v mc logic THP u ra ca mch l 0.9 V, l nguyn nhn gy ra cc vn trong mch logic. Hot ng camch logic tr nn khng tin cy khi tn hiu u ra c th ri vo vng cm. Hn na, s c mt ca in tr trong vng ccgccc pht c xu hng lm chm thit b, Do cc c tnh hn chcc cng RTL tr nn li thi.

Hnh 40.20 (a) Cng in tr-tranzito NOT, (b) Cng intr-tranzito NAND

Hnh 40.21 Logic it-in tr

Logic it-Tranzito (DTL)

Bn thn cc it c th c dng xy dng cc cng logic trong cc ng dng n gin nh thy trn hnh 40.20.Khi it dn in in p ri trn lp tip gip pn thng khong 0,7V, kt qu mc logic THP u ra l 0.7 V v mclogic CAO 4,3 V. Nh bit, s ni tng ca mt s mch ny s y mch vo vng cm, gy ra li logic. Hn na, logic

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Hnh 40.19 nh ngha thi giantruyn dn


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Thit k h thng logicin tr it khng th thc hin c hm o (NOT) v vic to ra cc ICvi mt cc it v in tr ln l iu khngth thc hin c. Do nhng hn ch ny m cng logic it-in tr tr ln li thi.

Cng DTL c minh ha trong hnh 40.21. Trong , cc it thc hin hm OR, tranzito thc hin hm NOT to racng NOR. S c mt ca in tr ti cc gc ca tranzito gy ra s tn hao nng lng v lm gim tc hot ng. Hnh40.22 minh ho mt thit k it-tranzito c ci tin loi tr in tr phn cc, nh tng tc hot ng. Cc thitb DTL b li thi do nhng hn ch ni trn.

Logic TranzitoTranzito (TTL)

T hnh 40.22, chng ta c th thy rng khi u vo mc THP, cc it ti u vo phn cc thun trong khi itti cc gc ca tranzito phn cc ngc . Ni cch khc, khi tt c cc u vo mc CAO, it ti cc gc s phn ccthun v tranzito dn in v thc hin chc nng ca hm NAND.

HNH 40.22 Cng logic NOR it-tranzito

HNH 40.23 Cng logic NAND it-tranzito c ci tin

Chng hn, khi mt tranzito npn dn, cc gc-cc pht s phn cc thun cn cc gp-cc gc phn cc ngc. Nuchng ta c mt tranzito vi nhiu cc pht, th chng ta c th s dng lp tip gip cc pht-cc gc cho cc it u vo.Lp tip gip cc gc-cc gp c dng cho cc gc-it trong cng DTL. Kt qu chng ta c cng TTL thc hin chcnng ca hm NAND nh thy hnh 40.23 [4].

Ti y, khi c bt k u vo no mc THP, vng cc gc-cc pht s dn in v in th ti cc pht ca tranzitotng th nhtl 0,2 V, u ra ca b o mc CAO . Khi tt c cc u vo mc CAO, th tranzito nhiu cc pht (tngth nht) ngt. Do , tt c nhng tranzito khc s dn in vi du ra mc logic THP. Cc bng d liu i vi tngthit b do nh sn xut cung cp cho chng ta s mch, v tt c cc thng s k thut bao gm gi tr u vo ti a v

ti thiu, tr lan truyn, thi gian tng trng v thi gian st, h s gp gii hn u vo, h s gp u ra, s tn haocng sut, v hng . y l nhng ngun thng tin c ch cho cc nh thit k.

Logic hai cc pht (ECL)

Thit b logic hai cc pht (ECL) l thit b lng cc trong tranzito khng bao gi bo ho hoc b ngt hon ton.Kt qu l tc cu n cao hn nhiu so vi TTL hoc CMOS. Cc cng ECL c dng trong mt vi ng dng cn tc cao nh b nh lu tr trong my tnh. Hnh 40.24minh ho cng NOR/OR [5]. VCC c ni t (0V) trong khi VEEli c ni vi in p cung cp in -5.2 V gim bt nhiu. Thi gian chuyn i t trng thi ny sang trng thi khcl khong di 1 ns, do tn s hot ng l khong mt vi gigahertz khi s dng cc cng ECL. Do cc tranzito khng bbo ha hon ton, nn cc u ra ca cng ELC mc CAO v mc THP tng ng l khong 0.75 v 1.6 V.

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S tay C in t

HNH 40.24 S thc thi logic Tranzitotranzito ca mt cng NAND [4]

HNH 40.25 Cng logic NOR/OR cc pht-cp i [5]

in p phn cc c t ti cc gc ca tranzito Q 4, gi tr ca n l trung bnh cng ca gi tr CAO v gi tr THPca cng; trong trng hp ny, gi tr ca n l vo khong 1.175 V. Tip theo, cc in tr c la chn iu khindng in v ngn chn tranzito bo ho. Khi tn hiu A hoc B l CAO (0.75 V), th cc tranzito s dn. in p ti imP s l 1.5 V (VBE ca Q2 + VA). iu ny lm gim hiu gia Vbb v in p im P di ngng cho php tranzito Q 3c th dn in v v th n b ngt, vin p im R tng n 0 V. Tranzito Q6 m. Vi ngng 0,75 V ca VBE, u rao c OR l 0.75 V, y l mc logic CAO. Gi tr ca in trRCvRE c la chn sao cho in p im Q l-0.85 V khi tranzito Q1 hay Q2ang dn. iu ny ng khi B CAO v A THP hoc khi cA vB u cao. Khi cA vB u THP, tranzito Q1 v Q2 u b ngt v tranzito Q3dn in lm gim in p im P xung1.925 V. inp im R l 0.85 V khin cho in p u ra OR l 1.6 V v in p u ra NOR l -0.75 V.

Bi v qu trnh hot ng ca transistor l khng i trong vng tch cc, dng in lin tc v gy ra s tn haonhit. Thit b ECL gim 4 n 5 ln cng sut so vi thit b TTL. V l do , cn thn trng khi dng n nh thit b ucui ni m tc l yu t ct yu trong khi c th s dng cng HCMOS hoc TTL bt k ni no.

tch hp cng ECL vi thit b TTL hoc CMOS, cn s dng b chuyn dch mc ring, v d b chuyn i ECLsang TTL 100325 cng sut thp ca hng bn dn National . Thit b chuyn i ny c u vo (-0.75 (H) v 1.6 (L) vu ra TTL (2.4 V min. i vi mc CAO (H) v 0.5 V max. i vi mc THP (L)), khi bo tr thi gian tng trng vthi gian st c th nh hn 1ns.

Hnh 40.26 B o NMOS

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Thit k h thng logic

Hnh 40.27 (a) Mt cng NMOS NAND, (b) Mt cng NMOS NOR

Hnh 40.28 Mt cng CMOS NOR

CMOS Logic

Trong nhng tho lun gn y, MOSFET c th c s dng ging nh mt chuyn mch transistor khng tn haocng sut. Cng logic NMOS c thit k vi MOSFET dng n v PMOS c thit k vi transistor MOSFET dng p. Vd, mt b o NMOS c gii thiu trn hnh 40.25. Hnh 40.26 (a) gii thiu mt hm logic NAND vi 2 MOSFET nini tip v hnh 40.26 (b) l cng NOR vi 2 MOSFET dng n ni song song. Mch NMOS c in tr y v n-MOSFETko. loi tr in tr, pha y ca mch c thay th bng p-MOSFET. Mch o hay NOT c biu din trn hnh40.27 [3]. Cc it thm vo nhm m bo s cn bng ca thit b. Mch ny c gi l mch CMOS do cc phn y v

ko ca mch c cc MOSFET b sung. Khi hai MOSFET dng n c ni ni tip pha ko ca mch , in tr y cthay th bng hai p-MOSFET song song v ngc li. Mt v d ca cng NOR dng CMOS c trnh by trn hnh 40.28.

Mt tnh cht quan trng ca cng CMOS l s tiu th nng lng thp ca chng khi thc t khng c dng in iqua c 2 trng thi cao v thp. Tuy nhin, thit b ny th chm hn transistor lng cc. Nh s tin b ca cng ngh snxut ngy nay kch thc ca transistor c gim xung v tc ca CMOS tip tc c ci thin.

40.7 Mch tch hp cng Logic

Mt cng IC logic thng mi bao gm nhiu cng cng dng. V d, trn hnh 40.29 gii thiu mt IC logic thngmi c 4 cng AND. Ngun nui chip c cp qua cc chn Vcc v chn ni t GND, A v B l cc chn u vo v Y ll chn u ra tng ng. Bn c th s dng mt hoc tt c cc cng trn chip nu cn thit. Khi la chn chip cnmt slu . V d khi chn mt cng AND ca Texas Instrumentsta thy c cc loi SN5408, SN54LS08, SN54S08, SN7408,SN74LS08, v SN74S08. Trn bng thng s ca thit b c nhiu thng tin hn nhng iu c trnh by y, cc thngtin c bn m chng ta cn quan tm l chc nng la chn (00 = cng NAND, 02 = NOR, 04 = B chuyn i, 08 =AND, etc.), v loi cng ngh (HC i vi CMOS tc cao, LS i vi Schottky cng sut thp, etc.). i vi cc s liukhc cachip, hy tham kho ti ti liu hng dn la chn ca hng Texas Instruments[1].

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Hnh 40.29 IC cng ANDdng DIP


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S tay C in t

40.8 Thit b Logic kh trnh (PLD)

Cc thit b logic kh trnh chnh l cc IC vi mt vi cng logic khng lin kt, cc lin kt gia nhng cng ny clp trnh da trn thit k mch logic. iu c bit c ngha khi xy dng v kim tra mt mch ln vi hng nghncng logic. Khi thit k v kim tra mch ln, s l khng thc t khi s dng cc cng IC logic chun v mi mt IC ch cti a 4 hoc 6 cng logic nn phi s dng mt s lng ln bn mch kt ni vi nhau. Mt PLD bao gm hng trm cnglogic v thit k trn thit b ny c th lp trnh c nh phn cng lp trnh c bit. Khi s dng nhiu hn mt PLD chovic thit k, cn lp trnh kt ni cc PLD. Mt dng trn vn ca PLD l mng logic kh trnh (PLA) bao gm mt lpAND gia v mt lp OR u ra, tng t nh mt cu trc cng logic n TTL, vi c hai lp c th lp trnh c. Ttc cc tn hiu u vo u c i qua mt lp o, lp ny s cung cp c gi tr chun v gi tr b ca bin u vo tilp AND. Cc kt ni thch hp c thc hin lp AND v lp OR thu c cc kt qu logic mong mun u ra.Trong thit b ny tt c cc lp u c th lp trnh c.

S ca PLA c ch ra trong hnh 40.30 [6] trong cc kt ni c to ra trong phn cng c nh du bng khiu X. Khi c lp trnh cc kt ni ny s c to ra hoc b ngt v c ch ra bng phn cng lp trnh c.

Mt phin bn n gin ca PLD c gi l thit b dy logic kh trnh, bao gm mt lp AND kh trnh v mt lp ORc nh. Thit b ny n gin v gim chi ph ch to, mc d n khng linh hot nh mt PLA. C th linh hot kt hpnh cc bin i cho ph hp vi mi yu cu. S ca mt PLA c gii thiu trong hnh 40.30, cc lin kt phncng c nh du X. Khi lp trnhcc kt ni ny c thit lp hoc ngt v c kim tra bng chng trnh lp trnhcho phn cng.

40.9 V d p dng C in t

Mch iu khin cho ng c mt chiul mt v d in hnh trong vic s dng transistor v cng logic. Yu cu cai tng cn thit k l:

1. ng c c th quay thun hoc ngc cc vn tc khc nhau.

2. ng c c th dng t t hoc c th hm t ngt

3. C th iu khin ng c quay vi nhng tc khc nhaunh b vi x l.

Hnh 40.30 Mng logic c th lp trnh c (PLA) [6]

Mt mch logic v mch cng sut hon chnh ca gii php thit k p ng nhng yu cu c trnh by trn hnh40.31, l mt mch cu H. ng c c ni vi cc chn u ra (u ra 1, u ra 2) [7]. Chn EN (enable), IN1 (u vo1) v IN2 (u vo 2) l cc u vo. Hot ng ca h thng ny c m t trn bng tip theo hnh 40.31. Khi m tn hiucho php mc THP, khng cn xt n cc trng thi u vo, tt c cc cng AND u mc THP, cc transistor cngsut ng v ng c s khng hot ng. Nu ng c ang hot ng m c tn hiu chuyn mch thp th ng c s t tdng li. Khi tn hiu cho php u vo cao, c th thy rng nu IN1 cao v IN2 thp th transistor 1 v 4 s m cn 2 v 3s ng. Lc ny ng c s c iu khin quay theo mt chiu v dng in chy qua ng c xung t thng qua 2tranzito cho nhau. Do transistor 2 v 3 ng nn trnh c vic ngn mch ngun. Vic ny c thit k bng cch aphn b ca IN1 v IN2 n cng AND iu khin transistor 3 v 4. Khi IN2 CAO v IN1 THP, ng c s quay ngcli(tn hiu cho php mc CAO). Khi transistor 2 v 4 ng v transistor 1 v 3 m, dng in chy qua ng c theochiu ngc li.

Khi tn hiu cho php mc CAO, m u vo IN1 v IN2 c th cng l cao hoc thp trong cng mt thi im, trongkhi ng c chuyn ng th cc cc ca ng c cng c ni vi ngun V cc hoc t. Tuy nhin, ng c s khng hot

ng nu c IN1 v IN2 cng THP. Khi , cc ng c c coi nh mt my pht in duy tr hiu in th qua cc ccca n khi rt chuyn ng trong t trng. Sc in ng sinh ra c a ti ngun. iu lm cho ng c dng limt cch nhanh chng, vic ging nh vic hm nhanh hay phanh. IN1 v IN2 cng c th c s dng phanh trctip khi tn hiu cho php c th l cc xung vi cc vng qut khc nhau (s iu bin b rng xung) t c cc tc khc nhau. Khi ng c quay t do tn hiu cho php thp khng xt n u vo, khi EN chuyn mch nhanh, qun tnh ca

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Thit k h thng logicroto gip cho chuyn ng u ra m. Vic la chn thi gian lp li (PRT) hay chu k v chn xung vi mt PRT nht nhs c c xung PWM iu khin hot ng ca h nh mong mun

Hnh 40.31 Mch iu khin ng c dng cu H [7]

Ti liu tham kho

[1] Logic Selection Guide, First Half 2001, Texas Instruments, Document sdyu001o.pdf. Source: www.ti.com.

[2] Designing with Logic, Texas Instruments, Document sdya009C.pdf. Source: www.ti.com

[3] CD4069UB Types- Quad-Inverter, Texas Instruments, Datasheet, schs054.pdf, 1998. Source: www.ti.com.

[4] SN5400 Quadruple 2-Input Positive NAND-Gates, Texas Instruments, Datasheet, sdls025.pdf, March 1988, Source:www.ti.com.

[5] Koga, R., Crain, W.R., Hansel, S.J., Crawford, K.B., Pinkerton, S.D., Peozin, S.H., Moses, S.C., and Maher, M., IonInduced Charge Collection and SEU Sensitivity of Emitter Coupled Logic (ECL) Devices, IEEE Trans onNuclear Science, 42(6), 18231828, 1995.

[6] High-performance Impact-X Programmable Array Logic Circuits, TIBPAL22V10-7C, TI, 1995. Productdatasheet.

[7] Dual Full-Bridge Driver L298, SGS Thomson Microelectronics Datasheet. Source: www.st.com.

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sổ tay cdt chuong 40-tke hthg logic

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