Въведение
Themostcommonlyusedsubstratematerialforintegratedcircuitdesignissilicon.Thedesignerwillusetechnicalmeanstoelectricallyisolatethevariousdevicesonthesiliconsubstratefromeachothertocontroltheelectricalconductivitybetweenthevariousdevicesontheentirechip.PNjunctions,metaloxidesemiconductorfieldeffecttransistors,etc.constitutethebasicstructureofintegratedcircuitdevices,whilethecomplementarymetaloxidesemiconductorcomposedofthelatterhasbecomeadigitalintegratedcircuitduetoitsadvantagesoflowstaticpowerconsumptionandhighintegration.Thebasicstructureoflogicgates.Designersneedtoconsidertheenergydissipationoftransistorsandinterconnections.Thisisdifferentfromthepreviousdiscreteelectronicdevicestobuildcircuits.Thisisbecauseallthecomponentsofanintegratedcircuitareintegratedonasiliconchip.Electromigrationandelectrostaticdischargeofmetalinterconnectsaregenerallyharmfultodevicesonmicrochips,andthereforearealsoissuesthatneedtobepaidattentiontoinintegratedcircuitdesign.
Asthescaleofintegratedcircuitscontinuestoincrease,itsintegrationhasreachedthedeepsubmicronlevel(featuresizebelow130nanometers),andthenumberoftransistorsintegratedonasinglechiphasapproachedonebillion.Becauseofitsextremecomplexity,thedesignofintegratedcircuitsoftenrequirescomputer-aideddesignmethodologyandtechnicalmeanscomparedwithsimplecircuitdesigns.Theresearchscopeofintegratedcircuitdesigncoverstheoptimizationofdigitallogicindigitalintegratedcircuits,therealizationofnetlists,thewritingofhardwaredescriptionlanguagecodesattheregistertransferlevel,theverification,simulationandtiminganalysisoflogicfunctions,andthedistributionofcircuitsinthehardware.Theplacementofoperationalamplifiers,electronicfiltersandotherdevicesinthechipinanalogintegratedcircuitsandtheprocessingofmixedsignals.Relatedresearchalsoincludeselectronicdesignautomation(EDA)ofhardwaredesign,computer-aideddesign(CAD)methodology,etc.,whichareasubsetofelectricalengineeringandcomputerengineering.
Fordigitalintegratedcircuits,designersaremoreatthehigh-levelabstractionlevel,thatis,theregistertransferlevelorevenhighersystemlevel(somepeoplealsocallitthebehaviorlevel),usinghardwaredescriptionlanguageOrhigh-levelmodelinglanguagetodescribethelogicandtimingfunctionsofthecircuit,andlogicsynthesiscanautomaticallyconvertthehardwaredescriptionlanguageattheregistertransferlevelintoanetlistatthelogicgatelevel.Forsimplecircuits,designerscanalsousehardwaredescriptionlanguagetodirectlydescribetheconnectionbetweenlogicgatesandflip-flops.Afterfurtherfunctionalverification,layout,androutingofthenetlist,GDSIIfilesforindustrialmanufacturingcanbegenerated,andfactoriescanmanufacturecircuitsonwafersbasedonthefiles.Thedesignofanalogintegratedcircuitsinvolvesamorecomplexsignalenvironment,requireshigherengineers'experience,andthedegreeofautomationofitsdesignisfarlessthanthatofdigitalintegratedcircuits.
Afterthefunctionaldesignisgraduallycompleted,thedesignruleswillspecifywhichdesignsmatchthemanufacturingrequirementsandwhichonesdonotmatch,andthisruleitselfisalsoverycomplicated.TheICdesignprocessneedstomatchhundredsoftheserules.Undercertaindesignconstraints,thelayoutandroutingofthephysicallayoutofanintegratedcircuitisessentialtoobtainidealspeed,signalintegrity,andreducechiparea.Theunpredictabilityofsemiconductordevicemanufacturingmakesintegratedcircuitdesignmoredifficult.Inthefieldofintegratedcircuitdesign,duetothepressureofmarketcompetition,electronicdesignautomationandotherrelatedcomputer-aideddesigntoolshavebeenwidelyused.Engineerscanperformregistertransfer-leveldesign,functionalverification,statictiminganalysis,andphysicaldesignwiththeassistanceofcomputersoftware.Andotherprocesses.
Нивофабстракция
Integratedcircuitdesignusuallytakes"module"asthedesignunit.Forexample,foramulti-bitfulladder,thesecondarymoduleisaone-bitadder,andtheadderiscomposedofthenextlevelofANDandNOTmodules.TheNANDandNOTgatescanfinallybedecomposedintolowerabstractions.GradeCMOSdevice.
Fromanabstractlevel,digitalintegratedcircuitdesigncanbetop-down,thatis,thefunctionalmodulesofthehighestlogiclevelofthesystemaredefinedfirst,andthesub-modulesaredefinedaccordingtotherequirementsofthetop-levelmodules,andthenlayerbylayerContinuetodecompose;thedesigncanalsobebottom-up,thatis,themostspecificmodulesaredesignedfirst,andthentheselowest-levelmodulesareusedasbuildingblockstorealizetheupper-levelmodules,andfinallyreachthehighestlevel.Inmanydesigns,top-downandbottom-updesignmethodologiesaremixed.Thesystem-leveldesignersplantheoverallarchitectureanddividethesub-modules,whilethebottom-levelcircuitdesignersdesignupwardslayerbylayer.,Optimizeindividualmodules.Finally,designersfromthetwodirectionsmeetatacertainlevelofabstractioninthemiddletocompletetheentiredesign.
Хардуерно внедряване
Fordifferentdesignrequirements,engineerscanchoosetouseasemi-customdesignapproach,suchasusingprogrammablelogicdevices(fieldprogrammablelogicgatearrays,etc.)orbasedonstandardcellsThelibrary'sapplication-specificintegratedcircuitisusedtoimplementthehardwarecircuit;youcanalsouseafullycustomizeddesigntocontrolthetransistorlayouttoallthedetailsofthesystemstructure.
Пълен персонализиран дизайн
Thisdesignmethodrequiresthedesignertousethelayouteditortocompletethelayoutdesign,parameterextraction,unitcharacterization,andthenusethesebythemselvesDesigntheunittocompletethecircuitconstruction.Usually,thefullcustomdesignistomaximizeandoptimizethecircuitperformance.Ifacertainrequiredunitismissingfromthestandardunitlibrary,itisalsonecessarytoadoptafullycustomizeddesignmethodtocompletetherequiredunitdesign.However,thisdesignmethodusuallytakesalongtime.
Полуперсонализиран дизайн
Thedesignmethodoppositetofull-customdesignissemi-customdesign.Inshort,semi-customintegratedcircuitdesignisbasedonsomepre-designedlogiccells.Forexample,designerscandesignapplication-specificintegratedcircuitsbasedonstandardcomponentlibraries(usuallyavailableforpurchasefromthirdparties),andselecttherequiredlogicunits(suchasvariousbasiclogicgates,flip-flops,etc.)tobuildtherequiredcircuits..Theycanalsouseprogrammablelogicdevicestocompletethedesign.Almostallphysicalstructuresofsuchdeviceshavebeenfixedinthechip,andonlysomeoftheconnectionscanbeprogrammedbytheusertodetermineitsconnection.Theperformanceparametersrelatedtothesepre-designedlogicunitsareusuallyprovidedbytheirsupplierstofacilitatethedesignerstoperformtimingandpoweranalysis.Theadvantagesofimplementingadesignonasemi-customfieldprogrammablelogicgatearray(FPGA)aretheshortdevelopmentcycleandlowcost.
Програмируеми логически устройства
Програмируеми логически устройстваareusuallyprovidedbysemiconductormanufacturersascommoditychips.ThesechipscanbeconnectedtothecomputerthroughJTAGandothermethods,sothedesignPeoplecanuseelectronicdesignautomationtoolstocompletethedesign,andthenusethedesigncodetoprogramthelogicchip.Theprogrammablelogicarraychipisdefinedinadvancewiththearrayoflogicgatesbeforeleavingthefactory,andtheconnectionlinesbetweenthelogicgatescanbeprogrammedtocontroltheconnectionanddisconnection.Withthedevelopmentoftechnology,theprogrammingoftheconnectinglinecanbeachievedthroughEPROM(usinghigherpiezoelectricprogramming,ultravioletirradiationerasing),EEPROM(usingelectricalsignalsformultipleprogramminganderasing),SRAM,flashmemory,etc.Fieldprogrammablelogicgatearrayisaspecialprogrammablelogicdevice.Itsphysicalbasisisaconfigurablelogicunit,whichconsistsofalook-uptable,programmablemultiplexer,registerandotherstructures.Thelook-uptablecanbeusedtoimplementlogicfunctions.Forexample,alook-uptablewiththreeinputterminalscanimplementallthree-variablelogicfunctions.
Интегрална схема, специфична за приложението
Theadvantageoftheapplication-specificintegratedcircuit(ASIC)designedforspecialapplicationsisthatthearea,powerconsumption,andtimingcanbeoptimizedtothegreatestextent.Интегрална схема, специфична за приложениетоscanonlybemanufacturedaftertheentireintegratedcircuitdesigniscompleted,andrequirestheparticipationofprofessionalsemiconductorfactories.TheASICcanbebasedonastandardcelllibrary,oritcanbeafullycustomizeddesign.Inthelatterapproach,designershavemorecontroloverthelocationandconnectionofcomponentsonthewafer,unliketheprogrammablelogicdeviceapproach,wheretheycanonlychoosetousesomeofthehardwareresources,causingsomeresourcestobewasted.Thearea,powerconsumption,andtimingcharacteristicsofASICscanusuallybebetteroptimized.However,thedesignofapplication-specificintegratedcircuitswillbemorecomplicated,andadedicatedprocessmanufacturingdepartment(oroutsourcedtoafoundry)isrequiredtomanufactureGDSIIfilesintocircuits.OncetheASICchipismanufactured,thelogicfunctionofthecircuitcannotbereconfiguredlikeaprogrammablelogicdevice.Forasingleproduct,theeconomicandtimecostofimplementingintegratedcircuitsonapplication-specificintegratedcircuitsishigherthanthatofprogrammablelogicdevices.Therefore,intheearlydesignanddebuggingprocess,programmablelogicdevicesarecommonlyused,especiallyfieldprogrammablelogicgatearrays;Ifthedesignedintegratedcircuitwillbeputintomassproductioninthelaterstage,massproductionofapplication-specificintegratedcircuitswillbemoreeconomical.
Процес на проектиране
Integratedcircuitdesigncanberoughlydividedintotwocategories:digitalintegratedcircuitdesignandanalogintegratedcircuitdesign.However,theactualintegratedcircuitmayalsobeamixed-signalintegratedcircuit,somanycircuitdesignsusethesetwoprocessesatthesametime.
Аналогови интегрални схеми
Anothermajorbranchofintegratedcircuitdesignisanalogintegratedcircuitdesign.Thisbranchusuallyfocusesonpowerintegratedcircuitsandradiofrequencyintegratedcircuits.Wait.Sincereal-worldsignalsareanalog,inelectronicproducts,analog-to-digitalanddigital-to-analoginterconversionintegratedcircuitsarealsowidelyused.Аналогови интегрални схемиincludeoperationalamplifiers,linearrectifiers,phase-lockedloops,oscillatorcircuits,activefilters,etc.Comparedwithdigitalintegratedcircuitdesign,analogintegratedcircuitdesignhasagreatercorrelationwiththephysicalpropertiesofsemiconductordevices,suchasitsgain,circuitmatching,powerdissipation,impedance,andsoon.Amplificationandfilteringofanalogsignalsrequirethecircuittohaveacertaindegreeoffidelitytothesignal.Therefore,analogintegratedcircuitsusemorelarge-areadevicesthandigitalintegratedcircuits,andtheirintegrationisrelativelylow.
Beforetheadventofmicroprocessorsandcomputer-aideddesignmethods,analogintegratedcircuitswerecompletelyartificiallydesigned.Duetothelimitedabilityofpeopletodealwithcomplexproblems,theanalogintegratedcircuitsatthattimewereusuallyrelativelybasiccircuits,andtheoperationalamplifierintegratedcircuitwasatypicalexample.Underthecircumstancesatthetime,suchintegratedcircuitsmayinvolvemorethanadozentransistorsandinterconnectionsbetweenthem.Inordertomakethedesignofanalogintegratedcircuitsreachthelevelofindustrialproduction,engineersneedtotakemultipleiterationstotestandtroubleshoot.Reusingdesignsthathavebeendesignedandverifiedcanfurtherformmorecomplexintegratedcircuits.Afterthe1970s,thepriceofcomputershasgraduallydropped.Moreandmoreengineerscanusethismoderntooltoassistindesign.Forexample,theycanuseacompiledcomputerprogramtosimulate,andtheycanobtainhigherlevelsofartificialcalculationsanddesignsthanbefore.Accuracy.SPICEisthefirstsoftwareforsimulationofanalogintegratedcircuits(infact,thedesignofstandardcellsindigitalintegratedcircuitsalsorequiresSPICEforparametertesting),whichliterallymeans"simulationprogramfocusedonintegratedcircuits(English:SimulationProgramwithIntegratedCircuitEmphasis)"Computer-aideddesign-basedcircuitsimulationtoolscanadapttomorecomplexmodernintegratedcircuits,especiallyapplication-specificintegratedcircuits.Usingacomputerforsimulationcanalsoenablesomeerrorsintheprojectdesigntobediscoveredbeforethehardwareismanufactured,therebyreducingalotofcostscausedbyrepeatedtestingandtroubleshooting.Inaddition,computersareoftenabletocompletesomeextremelycomplexandtedioustasksthathumanscannotdo,makingitpossible,suchastheMonteCarlomethod.Theactualhardwarecircuitwillencounterdeviationsthatareinconsistentwiththeidealsituation,suchastemperaturedeviations,semiconductordopingconcentrationdeviationsinthedevice,andcomputersimulationtoolscanalsobesimulatedandprocessed.Inshort,computerizedcircuitdesignandsimulationcanmakethecircuitdesignperformancebetter,anditsmanufacturabilitycanbemoreguaranteed.Nevertheless,comparedwithdigitalintegratedcircuits,thedesignofanalogintegratedcircuitsrequiresmorestringentrequirementsforengineers'experienceandtheabilitytoweighcontradictions.
Цифрова схема
Roughlyspeaking,digitalintegratedcircuitscanbedividedintothefollowingbasicsteps:systemdefinition,registertransferleveldesign,andphysicaldesign.Accordingtotheabstractleveloflogic,thedesignisdividedintosystembehaviorlevel,registertransferlevel,andlogicgatelevel.Designersneedtowritefunctionalcodesreasonably,setupsynthesistools,verifylogictimingperformance,planphysicaldesignstrategies,andsoon.Ataspecificpointinthedesignprocess,itisalsonecessarytocheckanddebugmultipletimesintermsoflogicfunctions,timingconstraints,anddesignrulestoensurethatthefinaldesignresultsmeettheinitialdesignclosuregoals.
Системна дефиниция
Systemdefinitionistheinitialplanforintegratedcircuitdesign.Atthisstage,designersneedtoconsiderthemacrofunctionsofthesystem.Designersmayusesomehigh-levelabstractmodelinglanguagesandtoolstocompletethedescriptionofthehardware,suchasClanguage,C++,SystemC,SystemVerilogandothertransaction-levelmodelinglanguages,andtoolssuchasSimulinkandMATLABtomodelsignals.Althoughthemainstreamiscenteredonregistertransferleveldesign,someadvancedsynthesis(orbehaviorallevelsynthesis)andadvancedverificationtoolsthatdirectlytransformfromsystem-leveldescriptionstolow-abstraction-leveldescriptions(suchaslogicgate-levelstructuredescriptions)areinprogressionstage.Inthesystemdefinitionstage,designersalsoplantheexpectedperformanceindicatorsofthechip,suchastheprocess,powerconsumption,clockfrequency,andoperatingtemperature.
Registertransferleveldesign
Integratedcircuitdesignisoftencarriedoutattheregistertransferlevel,usinghardwaredescriptionlanguagetodescribethesignalstorageandsignalofdigitalintegratedcircuitsWhentransferringbetweenlogicalunitssuchasregisters,memories,combinationallogicdevices,andbuses.Whendesigningtheregistertransferlevelcode,thedesignerwillconvertthesystemdefinitionintoaregistertransferleveldescription.ThetwohardwaredescriptionlanguagesmostcommonlyusedbydesignersatthislevelofabstractionareVerilogandVHDL,whichwerestandardizedbytheInstituteofElectricalandElectronicsEngineers(IEEE)in1995and1987,respectively.Becauseofthehardwaredescriptionlanguage,thedesignercanfocusmoreontherealizationofthefunction,whichismorethanthepreviousmethodofdirectlydesigningthelogicgate-levelconnection(usingthehardwaredescriptionlanguagecanstilldirectlydesignthegate-levelnetlist,butFewpeopleworkthisway)withhigherefficiency.
Проверка на дизайна
Afterthedesignercompletestheregistertransferleveldesign,hewillusethetestplatform,assertions,etc.toperformfunctionalverificationtoverifywhethertheprojectdesignisconsistentwithThepreviousfunctiondefinitionsareconsistent.Ifthereisanerror,theloopholesinthepreviousdesignfilesneedtobedetected.IntheentiredesignprocessofmodernVLSI,verificationrequiresmoreandmoretimeandeffort,andevenexceedstheregistertransferleveldesignitself.Peoplehavesetupsomenewtoolsandlanguagesspecificallydevelopedforverification.
Forexample,toimplementsimpleaddersormorecomplexarithmeticlogicunits,oruseflip-flopstoimplementfinitestatemachines,designersmaywritehardwaredescriptionlanguagecodesofdifferentsizes.Functionalverificationisacomplextask.Verifiersneedtocreateavirtualexternalenvironmentforthedesigntobetested,provideinputsignalsforthedesigntobetested(thiskindofartificiallyaddedsignalisoftenrepresentedbytheterm"stimulus"),andthenobservethedesigntobetestedWhetherthefunctionofthedesignedoutputportconformstothedesignspecification.
Whenthedesignedcircuitisnotsimplewithafewinputportsandoutputports,sincetheverificationneedstoconsiderallinputconditionsasmuchaspossible,thedefinitionoftheexcitationsignalwillbecomemorecomplicated.Sometimesengineersusecertainscriptinglanguages(suchasPerl,Tcl)towriteverificationprograms,andusethehigh-speedprocessingofcomputerprogramstoachievegreatertestcoverage.Modernhardwareverificationlanguagescanprovidesomefeaturesspecificallyforverification,suchasrandomizedvariableswithconstraints,coverage,andsoon.Asaunifiedlanguageforhardwaredesignandverification,SystemVerilogisdevelopedonthebasisofVerilog,soithasboththedesigncharacteristicsandthecharacteristicsofthetestplatform,andintroducestheideaofobject-orientedprogramming,sothewritingofthetestplatformisclosersoftwaretest.Thedevelopmentframeworkofstandardizedverificationplatformsuchasgeneralverificationmethodologyisalsosupportedbymainstreamelectronicdesignautomationsoftwarevendors.Foradvancedsynthesis,electronicdesignautomationtoolsforadvancedverificationarealsounderstudy.
Логически синтез
Thehardwaredescriptionlanguagecodedesignedbyengineersisgenerallyattheregistertransferlevel.Beforethephysicaldesign,youneedtousealogicsynthesistooltoThetransmission-levelcodeisconvertedtoalogicgate-levelnetlistforaspecificprocess,andthelogicissimplified.
Similartomanuallogicoptimization,Karnaughmap,etc.areneeded.Electronicdesignautomationtoolstocompletelogicsynthesisalsorequirespecificalgorithms(suchasQuinn-McLaskialgorithm,etc.)tosimplifydesigners.Thedefinedlogicalfunction.Thefilesinputtotheautomaticsynthesistoolincluderegistertransfer-levelhardwaredescriptionlanguagecodes,processlibraries(whichcanbeprovidedbythird-partyfoundryserviceagencies),anddesignconstraintfiles.Thesefilesareindifferentelectronicdesignautomationtoolkits.Theformatinthesystemmayvary.Thelogicsynthesistoolwillgenerateanoptimizedgate-levelnetlist,butthisnetlistisstillbasedonthehardwaredescriptionlanguage.Theroutingofthisnetlistinthesemiconductorchipwillbecompletedinthephysicaldesign.
Choosetheprocesslibrarycorrespondingtodifferentdevices(suchasapplicationspecificintegratedcircuitsorfieldprogrammablegatearrays,etc.)forlogicsynthesis,orsetdifferentconstraintstrategiesduringsynthesis,whichwillproducedifferentsynthesisresults.Theregistertransferlevelcodewillaffecttheefficiencyofthenetlistaftersynthesis,suchasthelogicplandivisionandlanguagestructurestyleofthedesignproject.Mostofthematuresynthesistoolsarebasedontheregistertransferleveldescription,andtheadvancedsynthesistoolsbasedonthesystemleveldescriptionarestillinthedevelopmentstage.
Проверка на формална еквивалентност
Inordertocomparetheequivalenceofthegate-levelnetlistandtheregistertransferlevel,youcangeneratesuchasnon-dualitysatisfiability,Binarydecisiondiagramandotherwaystocompletetheformalequivalencecheck(formalverification).Infact,theequivalencecheckcanalsocheckthelogicalequivalencebetweentworegistertransfer-leveldesigns,orbetweentwogate-levelnetlists.
Времеви анализ
Theclockfrequencyofmodernintegratedcircuitshasreachedthemegahertzlevel,andthetimingrelationshipbetweenandwithinalargenumberofmodulesisextremelycomplicated.Therefore,inadditiontoverifyingthelogicfunctionofthecircuit,timinganalysisisalsorequired,thatis,thedelayofthesignalonthetransmissionpathischeckedtodeterminewhetheritmatchesthetimingclosurerequirements.Thestandarddelayformatinformationoflogicgatesrequiredfortiminganalysiscanbeprovidedbythestandardcelllibrary(ortiminginformationextractedfromtheuser-designedcell).Ascircuitfeaturesizescontinuetodecrease,theproportionofinterconnectdelaysintheactualtotaldelaybecomesmoreandmoresignificant.Therefore,afterthephysicaldesigniscompleted,thedelayoftheinterconnectscanbetakenintoaccounttoaccuratelyperformtiminganalysis..
Физически дизайн
Afterthelogicsynthesisiscompleted,byintroducingtheprocessinformationprovidedbythedevicemanufacturingcompany,thepreviouslycompleteddesignwillenterthelayoutplanning,layout,Inthewiringphase,engineersneedtoreasonablysettheparametersofthephysicaldesigntoolbasedontheconstraintsofdelay,powerconsumption,area,etc.,andcontinuouslydebugtoobtainthebestconfiguration,therebydeterminingthephysicallocationofthecomponentonthewafer.Ifitisafullcustomdesign,engineersalsoneedtocarefullydrawtheintegratedcircuitlayoutofthecellandadjustthetransistorsizetoreducepowerconsumptionanddelay.
Asthefeaturesizeofmodernintegratedcircuitscontinuestodecline,VLSIhasenteredthestageofdeepsub-micronlevel,andtheinfluenceofinterconnectiondelayoncircuitperformancehasreachedorevenexceededtheinfluenceoflogicgatedelay.Atthistime,thefactorsthatneedtobeconsideredincludethecapacitiveeffectofthelinenetworkandthelinenetworkinductanceeffect.Thevoltagedropcausedbythelargecurrentontheinternalpowerlineofthechipwillalsoaffectthestabilityoftheintegratedcircuit.Inordertosolvetheseproblemsandatthesametimealleviatethenegativeeffectsofclockskewandclocktreeparasiticparameters,reasonablelayoutandlogicdesign,functionalverificationandotherprocessesareequallyimportant.Withthedevelopmentofmobiledevices,low-powerdesignhasbecomemoreprominentinintegratedcircuitdesign.Inthephysicaldesignstage,thedesigncanbetransformedintoarepresentationmethodofgeometricfigures,andtheindustryhasanumberofstandardizedfileformats(suchasGDSII)toregulate.
Itisworthnotingthatthefunctionsimplementedbythecircuithavebeendeterminedinthepreviousregistertransferleveldesign.Inthephysicaldesignstage,engineersnotonlycannotallowthepreviouslydesignedlogicandtimingfunctionstobedamagedinthedesignatthisstage,butalsofurtheroptimizethechip'sperformanceintermsofdelaytime,powerconsumption,area,etc.whenitisrunningcorrectly.Afterthephysicaldesignhasproducedthepreliminarylayoutfile,theengineerneedstoverifythefunction,timing,designrules,signalintegrity,etc.oftheintegratedcircuitagaintoensurethatthephysicaldesigngeneratesthecorrecthardwarelayoutfile.
Тестваемост на дизайна и повторно използване на дизайна
Asthecomplexityofverylarge-scaleintegratedcircuitscontinuestoincrease,thetimeandeconomiccostsrequiredfortestingaftercircuitmanufacturingarealsoincreasing.Inthepast,peoplefocusedmostoftheirenergyonthedesignitself,anddidnotconsidersubsequenttests,becausethetestsatthattimewererelativelysimple.Inrecentyears,testingitselfhasgraduallybecomeahugesubject.
Forexample,itiseasiertocontrolcertaininternalsignalsfromtheoutsideofthecircuittomakethemexhibitspecificlogicalvalues,whilecertaininternalsignalsrelyonalargenumberofotherinternalsignals,anditisdifficulttodirectlychangetheirvaluesfromtheoutside.Inaddition,thechangeoftheinternalsignalcannotbeobservedatthemainoutputendinmanycases(sometimesthesignaloutputofthemainoutputendseemstobecorrect,buttheinternalstateiswrong,andonlyobservingtheoutputofthemainoutputendisnotenoughtojudgewhetherthecircuitisworkingproperly).Theabovetwotypesofproblems,namelycontrollabilityandobservability,arethetwomajorcomponentsoftestability.
Peoplegraduallydiscoveredthataddingsomespecialstructures(suchasscanchainandbuilt-inself-test)tothecircuitduringcircuitdesigncangreatlyfacilitatesubsequentcircuittesting.Suchdesignsarecalledtestabilitydesigns.Theymakethecircuitmorecomplex,butcanreducethecostoftheentireprojectwithsimplertesting.
WiththecontinuousimprovementoftheintegrationofVLSIandtheincreasingpressureofmarketcompetition,integratedcircuitdesignhasgraduallyintroducedreusabledesignmethodology.ThemainsignificanceofthereusabledesignmethodologyisthatthesupplierwhoprovidestheIPcore(intellectualpropertycore)canprovidesomepre-completeddesignstothedesignerintheformofcommodities,andthelattercanusetheIPcoreasacompletemoduleinUseinyourowndesignprojects.Asaresult,whenimplementingsimilarfunctions,companiesdonotneedtorepeatedlydesignsimilarmodules.Althoughdoingsowillincreasecommercialcosts,italsosignificantlyreducesthecomplexityofthedesign,therebyshorteningthecyclerequiredforthecompanytodesignlargecircuits,therebyimprovingmarketcompetitiveness.TheproductsprovidedbytheIPcoresuppliermaybeverifiedhardwaredescriptionlanguagecodes.Inordertoprotectthesupplier’sintellectualpropertyrights,thesecodesareoftenencrypted.TheIPcoreitselfisalsodesignedasanintegratedcircuit,butinordertobeappliedindifferentdesignprojects,itwillfocusonstrengtheningitsportability,soitsdesigncodespecificationsaremorestringent.SomechipcompaniesspecializeinthedevelopmentandsalesofIPcores.ARMisatypicalexample.Thesecompaniesmakeprofitsthroughtheauthorizationofintellectualpropertyrights.