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DIC

leoonechina
2017-09-27 0人阅读 举报 0 0 暂无简介

简介:本文档为《DICpdf》,可适用于IT/计算机领域

CHAPTERINTRODUCTIONnTheevolutionofdigitalcircuitdesignnCompellingissuesindigitalcircuitdesignnHowtomeasurethequalityofadesignValuablereferencesAHistoricalPerspectiveIssuesinDigitalIntegratedCircuitDesignQualityMetricsofaDigitalDesignSummaryToProbeFurtherchapterfmPageFriday,January,:AMINTRODUCTIONChapterAHistoricalPerspectiveTheconceptofdigitaldatamanipulationhasmadeadramaticimpactonoursocietyOnehaslonggrownaccustomedtotheideaofdigitalcomputersEvolvingsteadilyfrommainframeandminicomputers,personalandlaptopcomputershaveproliferatedintodailylifeMoresignificant,however,isacontinuoustrendtowardsdigitalsolutionsinallotherareasofelectronicsInstrumentationwasoneofthefirstnoncomputingdomainswherethepotentialbenefitsofdigitaldatamanipulationoveranalogprocessingwererecognizedOtherareassuchascontrolweresoontofollowOnlyrecentlyhavewewitnessedtheconversionoftelecommunicationsandconsumerelectronicstowardsthedigitalformatIncreasingly,telephonedataistransmittedandprocesseddigitallyoverbothwiredandwirelessnetworksThecompactdiskhasrevolutionizedtheaudioworld,anddigitalvideoisfollowinginitsfootstepsTheideaofimplementingcomputationalenginesusinganencodeddataformatisbynomeansanideaofourtimesIntheearlynineteenthcentury,Babbageenvisionedlargescalemechanicalcomputingdevices,calledDifferenceEnginesSwadeAlthoughtheseenginesusethedecimalnumbersystemratherthanthebinaryrepresentationnowcommoninmodernelectronics,theunderlyingconceptsareverysimilarTheAnalyticalEngine,developedin,wasperceivedasageneralpurposecomputingmachine,withfeaturesstrikinglyclosetomoderncomputersBesidesexecutingthebasicrepertoireofoperations(addition,subtraction,multiplication,anddivision)inarbitrarysequences,themachineoperatedinatwocyclesequence,calledldquostorerdquoandldquomillrdquo(execute),similartocurrentcomputersItevenusedpipeliningtospeeduptheexecutionoftheadditionoperation!Unfortunately,thecomplexityandthecostofthedesignsmadetheconceptimpracticalForinstance,thedesignofDifferenceEngineI(partofwhichisshowninFigure)required,mechanicalpartsatatotalcostofpound,(in!)FigureWorkingpartofBabbagersquosDifferenceEngineI(),thefirstknownautomaticcalculator(fromSwade,courtesyoftheScienceMuseumofLondon)chapterfmPageFriday,January,:AMSectionAHistoricalPerspectiveTheelectricalsolutionturnedouttobemorecosteffectiveEarlydigitalelectronicssystemswerebasedonmagneticallycontrolledswitches(orrelays)TheyweremainlyusedintheimplementationofverysimplelogicnetworksExamplesofsucharetrainsafetysystems,wheretheyarestillbeingusedatpresentTheageofdigitalelectroniccomputingonlystartedinfullwiththeintroductionofthevacuumtubeWhileoriginallyusedalmostexclusivelyforanalogprocessing,itwasrealizedearlyonthatthevacuumtubewasusefulfordigitalcomputationsaswellSooncompletecomputerswererealizedTheeraofthevacuumtubebasedcomputerculminatedinthedesignofmachinessuchastheENIAC(intendedforcomputingartilleryfiringtables)andtheUNIVACI(thefirstsuccessfulcommercialcomputer)Togetanideaaboutintegrationdensity,theENIACwasfeetlong,feethighandseveralfeetwideandincorporated,vacuumtubesItbecamerapidlyclear,however,thatthisdesigntechnologyhadreacheditslimitsReliabilityproblemsandexcessivepowerconsumptionmadetheimplementationoflargerengineseconomicallyandpracticallyinfeasibleAllchangedwiththeinventionofthetransistoratBellTelephoneLaboratoriesinBardeen,followedbytheintroductionofthebipolartransistorbySchockleyinSchockleyIttooktillbeforethisledtothefirstbipolardigitallogicgate,introducedbyHarrisHarris,andevenmoretimebeforethistranslatedintoasetofintegratedcircuitcommerciallogicgates,calledtheFairchildMicrologicfamilyNormanThefirsttrulysuccessfulIClogicfamily,TTL(TransistorTransistorLogic)waspioneeredinBeesonOtherlogicfamiliesweredevisedwithhigherperformanceinmindExamplesofthesearethecurrentswitchingcircuitsthatproducedthefirstsubnanoseconddigitalgatesandculminatedintheECL(EmitterCoupledLogic)familyMasakiTTLhadtheadvantage,however,ofofferingahigherintegrationdensityandwasthebasisofthefirstintegratedcircuitrevolutionInfact,themanufacturingofTTLcomponentsiswhatspearheadedthefirstlargesemiconductorcompaniessuchasFairchild,National,andTexasInstrumentsThefamilywassosuccessfulthatitcomposedthelargestfractionofthedigitalsemiconductormarketuntilthesUltimately,bipolardigitallogiclostthebattleforhegemonyinthedigitaldesignworldforexactlythereasonsthathauntedthevacuumtubeapproach:thelargepowerconsumptionpergateputsanupperlimitonthenumberofgatesthatcanbereliablyintegratedonasingledie,package,housing,orboxAlthoughattemptsweremadetodevelophighintegrationdensity,lowpowerbipolarfamilies(suchasILmdashIntegratedInjectionLogicHart),thetorchwasgraduallypassedtotheMOSdigitalintegratedcircuitapproachThebasicprinciplebehindtheMOSFETtransistor(originallycalledIGFET)wasproposedinapatentbyJLilienfeld(Canada)asearlyas,and,independently,byOHeilinEnglandinInsufficientknowledgeofthematerialsandgatestabilityproblems,however,delayedthepracticalusabilityofthedeviceforalongtimeOncetheseweresolved,MOSdigitalintegratedcircuitsstartedtotakeoffinfullintheearlysRemarkably,thefirstMOSlogicgatesintroducedwereoftheCMOSvarietyWanlass,andthistrendcontinuedtillthelatesThecomplexityofthemanufacturingprocessdelayedthefullexploitationofthesedevicesfortwomoredecadesInstead,AnintriguingoverviewoftheevolutionofdigitalintegratedcircuitscanbefoundinMurphy(Mostofthedatainthisoverviewhasbeenextractedfromthisreference)ItisaccompaniedbysomeofthehistoricallygroundbreakingpublicationsinthedomainofdigitalICrsquoschapterfmPageFriday,January,:AMINTRODUCTIONChapterthefirstpracticalMOSintegratedcircuitswereimplementedinPMOSonlylogicandwereusedinapplicationssuchascalculatorsThesecondageofthedigitalintegratedcircuitrevolutionwasinauguratedwiththeintroductionofthefirstmicroprocessorsbyIntelin(the)Fagginand(the)ShimaTheseprocessorswereimplementedinNMOSonlylogic,whichhastheadvantageofhigherspeedoverthePMOSlogicSimultaneously,MOStechnologyenabledtherealizationofthefirsthighdensitysemiconductormemoriesForinstance,thefirstKbitMOSmemorywasintroducedinHoffTheseeventswereatthestartofatrulyastoundingevolutiontowardseverhigherintegrationdensitiesandspeedperformances,arevolutionthatisstillinfullswingrightnowTheroadtothecurrentlevelsofintegrationhasnotbeenwithouthindrances,howeverInthelates,NMOSonlylogicstartedtosufferfromthesameplaguethatmadehighdensitybipolarlogicunattractiveorinfeasible:powerconsumptionThisrealization,combinedwithprogressinmanufacturingtechnology,finallytiltedthebalancetowardstheCMOStechnology,andthisiswherewestillaretodayInterestinglyenough,powerconsumptionconcernsarerapidlybecomingdominantinCMOSdesignaswell,andthistimetheredoesnotseemtobeanewtechnologyaroundthecornertoalleviatetheproblemAlthoughthelargemajorityofthecurrentintegratedcircuitsareimplementedintheMOStechnology,othertechnologiescomeintoplaywhenveryhighperformanceisatstakeAnexampleofthisistheBiCMOStechnologythatcombinesbipolarandMOSdevicesonthesamedieBiCMOSisusedinhighspeedmemoriesandgatearraysWhenevenhigherperformanceisnecessary,othertechnologiesemergebesidesthealreadymentionedbipolarsiliconECLfamilymdashGalliumArsenide,SiliconGermaniumandevensuperconductingtechnologiesThesetechnologiesonlyplayaverysmallroleintheoveralldigitalintegratedcircuitdesignsceneWiththeeverincreasingperformanceofCMOS,thisroleisboundtobefurtherreducedwithtimeHencethefocusofthistextbookonCMOSonlyIssuesinDigitalIntegratedCircuitDesignIntegrationdensityandperformanceofintegratedcircuitshavegonethroughanastoundingrevolutioninthelastcoupleofdecadesInthes,GordonMoore,thenwithFairchildCorporationandlatercofounderofIntel,predictedthatthenumberoftransistorsthatcanbeintegratedonasinglediewouldgrowexponentiallywithtimeThisprediction,latercalledMoorersquoslaw,hasproventobeamazinglyvisionaryMooreItsvalidityisbestillustratedwiththeaidofasetofgraphsFigureplotstheintegrationdensityofbothlogicICrsquosandmemoryasafunctionoftimeAscanbeobserved,integrationcomplexitydoublesapproximatelyeverytoyearsAsaresult,memorydensityhasincreasedbymorethanathousandfoldsinceAnintriguingcasestudyisofferedbythemicroprocessorFromitsinceptionintheearlyseventies,themicroprocessorhasgrowninperformanceandcomplexityatasteadyandpredictablepaceThetransistorcountsforanumberoflandmarkdesignsarecollectedinFigureThemilliontransistorchipbarrierwascrossedinthelateeightiesClockfrequenciesdoubleeverythreeyearsandhavereachedintotheGHzrangeThisisilluschapterfmPageFriday,January,:AMSectionIssuesinDigitalIntegratedCircuitDesigntratedinFigure,whichplotsthemicroprocessortrendsintermsofperformanceatthebeginningofthestcenturyAnimportantobservationisthat,asofnow,thesetrendshavenotshownanysignsofaslowdownItshouldbenosurprisetothereaderthatthisrevolutionhashadaprofoundimpactonhowdigitalcircuitsaredesignedEarlydesignsweretrulyhandcraftedEverytransistorwaslaidoutandoptimizedindividuallyandcarefullyfittedintoitsenvironmentThisisadequatelyillustratedinFigurea,whichshowsthedesignoftheIntelmicroprocessorThisapproachis,obviously,notappropriatewhenmorethanamilliondeviceshavetobecreatedandassembledWiththerapidevolutionofthedesigntechnology,timetomarketisoneofthecrucialfactorsintheultimatesuccessofacomponent(a)TrendsinlogicICcomplexity(b)TrendsinmemorycomplexityYearGbitsmicromMbitsmicromGbitsmicromMbitsmicromMbitsmicromMbitsmicromMbitsmicromKbitsmicromKbitsNumberofbitsperchipGbitsmicrom*EncyclopediahrsCDAudiosecHDTVEncyclopediahrsCDAudiosecHDTVHumanmemoryHumanDNAHumanmemoryHumanDNABookBookPagePageNumberofbitsperchipFigureEvolutionofintegrationcomplexityoflogicICsandmemoriesasafunctionoftimeFigureHistoricalevolutionofmicroprocessortransistorcount(fromIntel)YearofIntroductionTransistorsPentiumregtradePentiumIIPentiumIIIPentiumTransistorschapterfmPageFriday,January,:AMINTRODUCTIONChapterDesignershave,therefore,increasinglyadheredtorigiddesignmethodologiesandstrategiesthataremoreamenabletodesignautomationTheimpactofthisapproachisapparentfromthelayoutofoneofthelaterIntelmicroprocessors,thePentiumreg,showninFigurebInsteadoftheindividualizedapproachoftheearlierdesigns,acircuitisconstructedinahierarchicalway:aprocessorisacollectionofmodules,eachofwhichconsistsofanumberofcellsonitsownCellsarereusedasmuchaspossibletoreducethedesigneffortandtoenhancethechancesforafirsttimerightimplementationThefactthatthishierarchicalapproachisatallpossibleisthekeyingredientforthesuccessofdigitalcircuitdesignandalsoexplainswhy,forinstance,verylargescaleanalogdesignhasnevercaughtonTheobviousnextquestioniswhysuchanapproachisfeasibleinthedigitalworldandnot(ortoalesserdegree)inanalogdesignsThecrucialconcepthere,andthemostimportantoneindealingwiththecomplexityissue,isabstractionAteachdesignlevel,theinternaldetailsofacomplexmodulecanbeabstractedawayandreplacedbyablackboxviewormodelThismodelcontainsvirtuallyalltheinformationneededtodealwiththeblockatthenextlevelofhierarchyForinstance,onceadesignerhasimplementedamultipliermodule,itsperformancecanbedefinedveryaccuratelyandcanbecapturedinamodelTheperformanceofthismultiplierisingeneralonlymarginallyinfluencedbythewayitisutilizedinalargersystemForallpurposes,itcanhencebeconsideredablackboxwithknowncharacteristicsAsthereexistsnocompellingneedforthesystemdesignertolookinsidethisbox,designcomplexityissubstantiallyreducedTheimpactofthisdivideandconquerapproachisdramaticInsteadofhavingtodealwithamyriadofelements,thedesignerhastoconsideronlyahandfulofcomponents,eachofwhicharecharacterizedinperformanceandcostbyasmallnumberofparametersThisisanalogoustoasoftwaredesignerusingalibraryofsoftwareroutinessuchasinputoutputdriversSomeonewritingalargeprogramdoesnotbothertolookinsidethoselibraryroutinesTheonlythinghecaresaboutistheintendedresultofcallingoneofthosemodulesImaginewhatwritingsoftwareprogramswouldbelikeifonehadtofetcheverybitindividuallyfromthediskandensureitscorrectnessinsteadofrelyingonhandyldquofileopenrdquoandldquogetstringrdquooperatorsFigureMicroprocessorperformancetrendsatthebeginningofthestcenturyPPentiumregprocYearFrequency(Mhz)DoubleseveryyearsFrequency(Mhz)chapterfmPageFriday,January,:AMSectionIssuesinDigitalIntegratedCircuitDesign(b)ThePentiumregmicroprocessorFigureComparingthedesignmethodologiesoftheIntel()andPentiumreg(microprocessors(reprintedwithpermissionfromIntel)StandardCellModule(a)ThemicroprocessorMemoryModulechapterfmPageFriday,January,:AMINTRODUCTIONChapterTypicallyusedabstractionlevelsindigitalcircuitdesignare,inorderofincreasingabstraction,thedevice,circuit,gate,functionalmodule(eg,adder)andsystemlevels(eg,processor),asillustratedinFigureAsemiconductordeviceisanentitywithaverycomplexbehaviorNocircuitdesignerwilleverseriouslyconsiderthesolidstatephysicsequationsgoverningthebehaviorofthedevicewhendesigningadigitalgateInsteadhewilluseasimplifiedmodelthatadequatelydescribestheinputoutputbehaviorofthetransistorForinstance,anANDgateisadequatelydescribedbyitsBooleanexpression(Z=AB),itsboundingbox,thepositionoftheinputandoutputterminals,andthedelaybetweentheinputsandtheoutputThisdesignphilosophyhasbeentheenablerfortheemergenceofelaboratecomputeraideddesign(CAD)frameworksfordigitalintegratedcircuitswithoutitthecurrentdesigncomplexitywouldnothavebeenachievableDesigntoolsincludesimulationatthevariouscomplexitylevels,designverification,layoutgeneration,anddesignsynthesisAnoverviewofthesetoolsanddesignmethodologiesisgiveninChapterofthistextbookFurthermore,toavoidtheredesignandreverificationoffrequentlyusedcellssuchasbasicgatesandarithmeticandmemorymodules,designersmostoftenresorttocelllibrariesTheselibrariescontainnotonlythelayouts,butalsoprovidecompletedocumentationandcharacterizationofthebehaviorofthecellsTheuseofcelllibrariesis,fornnSGDDEVICECIRCUITGATEMODULESYSTEMFigureDesignabstractionlevelsindigitalcircuitschapterfmPageFriday,January,:AMSectionIssuesinDigitalIntegratedCircuitDesigninstance,apparentinthelayoutofthePentiumregprocessor(Figureb)Theintegerandfloatingpointunit,justtonameafew,containlargesectionsdesignedusingthesocalledstandardcellapproachInthisapproach,logicgatesareplacedinrowsofcellsofequalheightandinterconnectedusingroutingchannelsThelayoutofsuchablockcanbegeneratedautomaticallygiventhatalibraryofcellsisavailableTheprecedinganalysisdemonstratesthatdesignautomationandmodulardesignpracticeshaveeffectivelyaddressedsomeofthecomplexityissuesincurredincontemporarydigitaldesignThisleadstothefollowingpertinentquestionIfdesignautomationsolvesallourdesignproblems,whyshouldwebeconcernedwithdigitalcircuitdesignatallWillthenextgenerationdigitaldesignereverhavetoworryabouttransistorsorparasitics,oristhesmallestdesignentityhewilleverconsiderthegateandthemoduleThetruthisthattherealityismorecomplex,andvariousreasonsexistastowhyaninsightintodigitalcircuitsandtheirintricacieswillstillbeanimportantassetforalongtimetocomebullFirstofall,someonestillhastodesignandimplementthemodulelibrariesSemiconductortechnologiescontinuetoadvancefromyeartoyearUntilonehasdevelopedafoolproofapproachtowardsldquoportingrdquoacellfromonetechnologytoanother,eachchangeintechnologymdashwhichhappensapproximatelyeverytwoyearsmdashrequiresaredesignofthelibrarybullCreatinganadequatemodelofacellormodulerequiresanindepthunderstandingofitsinternaloperationForinstance,toidentifythedominantperformanceparametersofagivendesign,onehastorecognizethecriticaltimingpathfirstbullThelibrarybasedapproachworksfinewhenthedesignconstraints(speed,costorpower)arenotstringentThisisthecaseforalargenumberofapplicationspecificdesigns,wherethemaingoalistoprovideamoreintegratedsystemsolution,andperformancerequirementsareeasilywithinthecapabilitiesofthetechnologyUnfortunatelyforalargenumberofotherproductssuchasmicroprocessors,successhingesonhighperformance,anddesignersthereforetendtopushtechnologytoitslimitsAtthatpoint,thehierarchicalapproachtendstobecomesomewhatlessattractiveToresorttoourpreviousanalogytosoftwaremethodologies,aprogrammertendstoldquocustomizerdquosoftwareroutineswhenexecutionspeediscrucialcompilersmdashordesigntoolsmdasharenotyettothelevelofwhathumansweatoringenuitycandeliverbullEvenmoreimportantistheobservationthattheabstractionbasedapproachisonlycorrecttoacertaindegreeTheperformanceof,forinstance,anaddercanbesubstantiallyinfluencedbythewayitisconnectedtoitsenvironmentTheinterconnectionwiresthemselvescontributetodelayastheyintroduceparasiticcapacitances,resistancesandeveninductancesTheimpactoftheinterconnectparasiticsisboundtoincreaseintheyearstocomewiththescalingofthetechnologybullScalingtendstoemphasizesomeotherdeficienciesoftheabstractionbasedmodelSomedesignentitiestendtobeglobalorexternal(toresortanewtothesoftwareanalogy)Examplesofglobalfactorsaretheclocksignals,usedforsynchronizationinadigitaldesign,andthesupplylinesIncreasingthesizeofadigitaldesignhasachapterfmPageFriday,January,:AMINTRODUCTIONChapterprofoundeffectontheseglobalsignalsForinstance,connectingmorecellstoasupplylinecancauseavoltagedropoverthewire,which,initsturn,canslowdownalltheconnectedcellsIssuessuchasclockdistribution,circuitsynchronization,andsupplyvoltagedistributionarebecomingmoreandmorecriticalCopingwiththemrequiresaprofoundunderstandingoftheintricaciesofdigitalcircuitdesignbullAnotherimpactoftechnologyevolutionisthatnewdesignissuesandconstraintstendtoemergeovertimeAtypicalexampleofthisistheperiodicalreemergenceofpowerdissipationasaconstrainingfactor,aswasalreadyillustratedinthehistoricaloverviewAnotherexampleisthechangingratiobetweendeviceandinterconnectparasiticsTocopewiththeseunforeseenfactors,onemustatleastbeabletomodelandanalyzetheirimpact,requiringonceagainaprofoundinsightintocircuittopologyandbehaviorbullFinally,whenthingscangowrong,theydoAfabricatedcircuitdoesnotalwaysexhibittheexactwaveformsonemightexpectfromadvancesimulationsDeviationscanbecausedbyvariationsinthefabricationprocessparameters,orbytheinductanceofthepackage,orbyabadlymodeledclocksignalTroubleshootingadesignrequirescircuitexpertiseForalltheabovereasons,itismybeliefthatanindepthknowledgeofdigitalcircuitdesigntechniquesandapproachesisanessentialassetforadigitalsystemdesignerEventhoughshemightnothavetodealwiththedetailsofthecircuitonadailybasis,theunderstandingwillhelphertocopewithunexpectedcircumstancesandtodeterminethedominanteffectswhenanalyzingadesignExampleClocksDefyHierarchyToillustratesomeoftheissuesraisedabove,letusexaminetheimpactofdeficienciesinoneofthemostimportantglobalsignalsinadesign,theclockThefunctionoftheclocksignalinadigitaldesignistoorderthemultitudeofeventshappeninginthecircuitThistaskcanbecomparedtothefunctionofatrafficlightthatdetermineswhichcarsareallowedtomoveItalsomakessurethatalloperationsarecompletedbeforethenextonestartsmdashatrafficlightshouldbegreenlongenoughtoallowacarorapedestriantocrosstheroadUnderidealcircumstances,theclocksignalisaperiodicstepwaveformwithtransitionssynchronizedthroughoutthedesignedcircuit(Figurea)Inlightofouranalogy,changesinthetrafficlightsshouldbesynchronizedtomaximizethroughputwhileavoidingaccidentsTheimportanceoftheclockalignmentconceptisillustratedwiththeexampleoftwocascadedregisters,bothoperatingontherisingedgeoftheclockphi(Figureb)Undernormaloperatingconditions,theinputIngetssampledintothefirstregist

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