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1、SECTION7HIGHSPEEDHARDWAREDESIGNTECHNIQUESWaltKester,JamesBryant,WaltJung,AdolfoGarcia,JohnMcDonald,JoeBuxtonANALOGCIRCUITSIMULATIONWaltKester,JoeBuxtonInrecentyearstherehasbeenmuchpressureplacedonsystemdesignerstoverifytheirdesignswithcomputersimulationsbeforecommittingtoactual
2、printedcircuitboardlayoutsandhardware.Simulatingcomplexdigitaldesignsisextremelybeneficial,andveryoften,theprototypephasecanbeeliminatedentirely.However,bypassingtheprototypephaseinhigh-speed/high-performanceanalogormixed-signalcircuitdesignscanberiskyforanumberofreasons.Forthe
3、purposesofthisdiscussion,ananalogcircuitisanycircuitwhichusesICssuchasopamps,instrumentationamps,programmablegainamps(PGAs),voltagecontrolledamps(VCAs),logamps,mixers,analogmultipliers,etc.Amixed-signalcircuitisanA/Dconverter(ADC),D/Aconverter(DAC),orcombinationsoftheseinconjun
4、ctionwithsomeamountofdigitalsignalprocessingwhichmayormaynotbeonthesameICastheconverters.ConsideratypicalICoperationalamplifier.Itmaycontainsome20-40transistors,almostasmanyresistors,andafewcapacitors.AcompleteSPICE(SimulationProgramwithIntegratedCircuitEmphasis,seeReference1)m
5、odelwillcontainallthesecomponents,andprobablyafewofthemoreimportantparasiticcapacitancesandspuriousdiodesformedbythevariousjunctionsintheop-ampchip.Forhigh-speedICs,thepackageandwirebondparasiticsmayalsobeincluded.ThisisthetypeofmodelthattheICdesignerusestooptimizethedeviceduri
6、ngthedesignphaseandistypicallyrunonaCADworkstation.Becauseitisadetailedmodel,itwillbereferredtoasamicromodel.Insimulations,suchamodelwillbehaveverymuchliketheactualop-amp,butnotexactly.TheICdesignerusestransistorandotherdevicemodelsbasedontheactualprocessuponwhichthecomponentis
7、fabricated.SemiconductormanufacturersinvestconsiderabletimeandmoneydevelopingandrefiningthesedevicemodelssothattheICdesignerscanhaveahighdegreeofconfidencethatthefirstsiliconwillworkandthatmaskchanges(costingadditionaltimeandmoney)requiredforthefinalmanufacturedproductareminimi
8、zed.However,thesedevicemodelsarenotpublished,neitherar
