Integrated Circuits集成电路电子信息类专业英语计算机类专业英语文章.docx
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Integrated Circuits集成电路电子信息类专业英语计算机类专业英语文章.docx
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IntegratedCircuits集成电路电子信息类专业英语计算机类专业英语文章
IntegratedCircuits(集成电路)
英文原稿:
TheIntegratedCircuit
Digitallogicandelectroniccircuitsderivetheirfunctionalityfromelectronicswitchescalledtransistor.Roughlyspeaking,thetransistorcanbelikenedtoanelectronicallycontrolledvalvewherebyenergyappliedtooneconnectionofthevalveenablesenergytoflowbetweentwootherconnections.Bycombiningmultipletransistors,digitallogicbuildingblockssuchasANDgatesandflip-flopsareformed.Transistors,inturn,aremadefromsemiconductors.Consultaperiodictableofelementsinacollegechemistrytextbook,andyouwilllocatesemiconductorsasagroupofelementsseparatingthemetalsandnonmetals.Theyarecalledsemiconductorsbecauseoftheirabilitytobehaveasbothmetalsandnonmetals.Asemiconductorcanbemadetoconductelectricitylikeametalortoinsulateasanonmetaldoes.Thesedifferingelectricalpropertiescanbeaccuratelycontrolledbymixingthesemiconductorwithsmallamountsofotherelements.Thismixingiscalleddoping.Asemiconductorcanbedopedtocontainmoreelectrons(N-type)orfewerelectrons(P-type).Examplesofcommonlyusedsemiconductorsaresiliconandgermanium.PhosphorousandboronaretwoelementsthatareusedtodopeN-typeandP-typesilicon,respectively.
Atransistorisconstructedbycreatingasandwichofdifferentlydopedsemiconductorlayers.Thetwomostcommontypesoftransistors,thebipolar-junctiontransistor(BJT)andthefield-effecttransistor(FET)areschematicallyillustratedinFigure2.1.Thisfigureshowsboththesiliconstructuresoftheseelementsandtheirgraphicalsymbolicrepresentationaswouldbeseeninacircuitdiagram.TheBJTshownisanNPNtransistor,becauseitiscomposedofasandwichofN-P-Ndopedsilicon.Whenasmallcurrentisinjectedintothebaseterminal,alargercurrentisenabledtoflowfromthecollectortotheemitter.TheFETshownisanN-channelFET,whichiscomposedoftwoN-typeregionsseparatedbyaP-typesubstrate.Whenavoltageisappliedtotheinsulatedgateterminal,acurrentisenabledtoflowfromthedraintothesource.ItiscalledN-channel,becausethegatevoltageinducesanN-channelwithinthesubstrate,enablingcurrenttoflowbetweentheN-regions.
Anotherbasicsemiconductorstructureisadiode,whichisformedsimplybyajunctionofN-typeandP-typesilicon.Diodesactlikeone-wayvalvesbyconductingcurrentonlyfromPtoN.Specialdiodescanbecreatedthatemitlightwhenavoltageisapplied.Appropriatelyenough,thesecomponentsarecalledlightemittingdiodes,orLEDs.Thesesmalllightsaremanufacturedbythemillionsandarefoundindiverseapplicationsfromtelephonestotrafficlights.
Theresultingsmallchipofsemiconductormaterialonwhichatransistorordiodeisfabricatedcanbeencasedinasmallplasticpackageforprotectionagainstdamageandcontaminationfromtheoutsideworld.Smallwiresareconnectedwithinthispackagebetweenthesemiconductorsandwichandpinsthatprotrudefromthepackagetomakeelectricalcontactwithotherpartsoftheintendedcircuit.Onceyouhaveseveraldiscretetransistors,digitallogiccanbebuiltbydirectlywiringthesecomponentstogether.Thecircuitwillfunction,butanysubstantialamountofdigitallogicwillbeverybulky,becauseseveraltransistorsarerequiredtoimplementeachofthevarioustypesoflogicgates.
Atthetimeoftheinventionofthetransistorin1947byJohnBardeen,WalterBrattain,andWilliamShockley,theonlywaytoassemblemultipletransistorsintoasinglecircuitwastobuyseparatediscretetransistorsandwirethemtogether.In1959,JackKilbyandRobertNoyceindependentlyinventedameansoffabricatingmultipletransistorsonasingleslabofsemiconductormaterial.Theirinventionwouldcometobeknownastheintegratedcircuit,orIC,whichisthefoundationofourmoderncomputerizedworld.AnICissocalledbecauseitintegratesmultipletransistorsanddiodesontothesamesmallsemiconductorchip.Insteadofhavingtosolderindividualwiresbetweendiscretecomponents,anICcontainsmanysmallcomponentsthatarealreadywiredtogetherinthedesiredtopologytoformacircuit.
AtypicalIC,withoutitsplasticorceramicpackage,isasquareorrectangularsilicondiemeasuringfrom2to15mmonanedge.DependingontheleveloftechnologyusedtomanufacturetheIC,theremaybeanywherefromadozentotensofmillionsofindividualtransistorsonthissmallchip.Thisamazingdensityofelectroniccomponentsindicatesthatthetransistorsandthewiresthatconnectthemareextremelysmallinsize.DimensionsonanICaremeasuredinunitsofmicrometers,withonemicrometer(1mm)beingonemillionthofameter.Toserveasareferencepoint,ahumanhairisroughly100mmindiameter.SomemodernICscontaincomponentsandwiresthataremeasuredinincrementsassmallas0.1mm!
Eachyear,researchersandengineershavebeenfindingnewwaystosteadilyreducethesefeaturesizestopackmoretransistorsintothesamesiliconarea,asindicatedinFigure2.2.
WhenanICisdesignedandfabricated,itgenerallyfollowsoneoftwomaintransistortechnologies:
bipolarormetal-oxidesemiconductor(MOS).BipolarprocessescreateBJTs,whereasMOSprocessescreateFETs.Bipolarlogicwasmorecommonbeforethe1980s,butMOStechnologieshavesinceaccountedthegreatmajorityofdigitallogicICs.N-channelFETsarefabricatedinanNMOSprocess,andP-channelFETsarefabricatedinaPMOSprocess.Inthe1980s,complementary-MOS,orCMOS,becamethedominantprocesstechnologyandremainssotothisday.CMOSICsincorporatebothNMOSandPMOStransistors.
ApplicationSpecificIntegratedCircuit
Anapplication-specificintegratedcircuit(ASIC)isanintegratedcircuit(IC)customizedforaparticularuse,ratherthanintendedforgeneral-purposeuse.Forexample,achipdesignedsolelytorunacellphoneisanASIC.Incontrast,the7400seriesand4000seriesintegratedcircuitsarelogicbuildingblocksthatcanbewiredtogetherforuseinmanydifferentapplications.
Asfeaturesizeshaveshrunkanddesigntoolsimprovedovertheyears,themaximumcomplexity(andhencefunctionality)possibleinanASIChasgrownfrom5,000gatestoover100million.ModernASICsoftenincludeentire32-bitprocessors,memoryblocksincludingROM,RAM,EEPROM,Flashandotherlargebuildingblocks.SuchanASICisoftentermedaSoC(System-on-Chip).DesignersofdigitalASICsuseahardwaredescriptionlanguage(HDL),suchasVerilogorVHDL,todescribethefunctionalityofASICs.
Field-programmablegatearrays(FPGA)arethemoderndayequivalentof7400serieslogicandabreadboard,containingprogrammablelogicblocksandprogrammableinterconnectsthatallowthesameFPGAtobeusedinmanydifferentapplications.Forsmallerdesignsand/orlowerproductionvolumes,FPGAsmaybemorecosteffectivethananASICdesign.Thenon-recurringengineeringcost(thecosttosetupthefactorytoproduceaparticularASIC)canrunintohundredsofthousandsofdollars.
ThegeneraltermapplicationspecificintegratedcircuitincludesFPGAs,butmostdesignersuseASIConlyfornon-fieldprogrammabledevicesandmakeadistinctionbetweenASICandFPGAs.
History
TheinitialASICsusedgatearraytechnology.Ferrantiproducedperhapsthefirstgate-array,theULA(UncommittedLogicArray),around1980.Customizationoccurredbyvaryingthemetalinterconnectmask.ULAshadcomplexitiesofuptoafewthousandgates.Laterversionsbecamemoregeneralized,withdifferentbasediescustomizedbybothmetalandpolysiliconlayers.SomebasediesincludeRAMelements.
Standardcelldesign
Inthemid1980sadesignerwouldchooseanASICmanufacturerandimplementtheirdesignusingthedesigntoolsavailablefromthemanufacturer.Whilethirdpartydesigntoolswereavailable,therewasnotaneffectivelinkfromthethirdpartydesigntoolstothelayoutandactualsemiconductorprocessperformancecharacteristicsofthevariousASICmanufacturers.Mostdesignersendedupusingfactoryspecifictoolstocompletetheimplementationoftheirdesigns.AsolutiontothisproblemthatalsoyieldedamuchhigherdensitydevicewastheimplementationofStandardCells.EveryASICmanufacturercouldcreatefunctionalblockswithknownelectricalcharacteristics,suchaspropagationdelay,capacitanceandinductance;thatcouldalsoberepresentedinthirdpartytools.Standardcelldesignistheutilizationofthesefunctionalblockstoachieveveryhighgatedensityandgoodelectricalperformance.StandardcelldesignfitsbetweenGateArrayandFullCustomdesignintermsofbothitsNRE(Non-RecurringEngineering)andrecurringcomponentcost.
Bythelate1980s,logicsynthesistools,suchasDesignCompiler,becameavailable.SuchtoolscouldcompileHDLdescriptionsintoagate-levelnetlist.Thisenabledastyleofdesigncalledstandard-celldesign.Standard-cellIntegratedCircuits(ICs)aredesignedinthefollowingconceptualstages,althoughthesestagesoverlapsignificantlyinpractice.
Thesesteps,implementedwithalevelofskillcommonintheindustry,almostalwaysproduceafinaldevicethatcorrectlyimplementstheoriginaldesign,unlessflawsarelaterintroducedbythephysicalfabricationprocess.
Ateamofdesignengineersstartswithanon-formalunderstandingoftherequiredfunctionsforanewASIC,usuallyderivedfromrequirementsanalysis.
*ThedesignteamconstructsadescriptionofanASICtoachievethesegoalsusinganHDL.Thisprocessisanalogoustowritingacomputerprograminahigh-levellanguage.ThisisusuallycalledtheRTL(registertransferlevel)design.
*Suitabilityfor
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