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1、Vol.30,No.2JournalofSemiconductorsFebruary2009AhighefciencyPWMCMOSclass-DaudiopoweramplierZhuZhangming(朱樟明)1,LiuLianxi(劉簾曦)1,YangYintang(楊銀堂)1,andLeiHan(雷晗)2(1InstituteofMicroelectronics,XidianUniversity,Xian710071,China)(2XianPower-RailMicroCo.,Ltd,Xian710075,China)Abstract:Basedonthedifferenceclos

2、e-loopfeedbacktechniqueandthedifferencepre-amp,ahighefciencyPWMCMOSclass-Daudiopoweramplierisproposed.Arail-to-railPWMcomparatorwithwindowfunctionhasbeenembeddedintheclass-Daudiopoweramplier.DesignresultsbasedontheCSMC0.5µmCMOSprocessshowthatthemaxefciencyis90%,thePSRRis75dB,thepowersupplyvolta

3、gerangeis2.55.5V,theTHD+Nin1kHzinputfrequencyislessthan0.20%,thequiescentcurrentinnoloadis2.8mA,andtheshutdowncurrentis0.5µA.Theactiveareaoftheclass-Daudiopoweramplierisabout1.47×1.52mm2.Withthegoodperformance,theclass-Daudiopowerampliercanbeappliedtoseveralaudiopowersystems.Keywords:class

4、-Daudioamplier;PWM;CMOS;highefciency;rail-to-railcomparator;differenceDOI:10.1088/1674-4926/30/2/025001EEACC:1210;1220;12901.IntroductionConventionalclass-A,B,orABaudioampliersdirectlyamplifytheanalogsignalsandmustworkinthetriodere-gion.Althoughclass-ABaudioampliershavehighdelity,theirpowerdissipati

5、onisobviousandconversionefciencyisbelow50%,whichhardlysatisfytherequirementofenergy-saving.Somemethods(suchasemployingpush-pulloutputstage)areappliedtocompensateclass-ABampliers,butwhenthepowerishigh,powerdevicesarestillthreatenedandpoweroutputislimited,therebythepracticalconversionef-ciencyis30%40%

6、nomatterthatthetheoreticalvaluewouldbe78.5%,leadingtoaseriousenergywasteproblem.Atthesametimewemustincreasethechipareaorevenaddaplusradiatingangefortheeliminationofheat,thustoomuchareaistakenandalsothecostisunaffordable.Ontheotherhand,class-DampliershavemanyadvantagesovertheclassA,B,orABmentionedabo

7、ve,thecharacteristicworkingontheswitchingstatemakethetheoreticefciencycouldbe100%,thepracticalvaluecouldbeover80%,andsopowerdissipa-tion,chipareaandareatakenbyPCBcouldbegreatlyre-duced.Sincepresentelectronicindustryaimsatsmallvolume,lowpowerandhighefciency,class-Dampliershaveabrightfuture19.Atpresen

8、t,class-DaudiopowerampliershavealreadybeenusedinconsumerelectronicproductssuchasDVD,LCD-TV,MP4andcellphone.Comparedtotheconventionalclass-ABaudiopoweramplier,itsgreatestadvantageisthehighefciency,thepracticalefciencywouldbeover80%,andthetheoreticalefciencywouldbe100%.Intheclass-Daudiopoweramplier,we

9、comparetheaudiosignalandhighfrequencyconstantsignal,thenmodulatethiscomparedresultusingtheconstantfrequencycarrierwaves,thusdigitalsignalisconvertedintoPWMsignal,whichisofchangeablepulsewidthandconstantcarrierfrequency(hundredskHzgener-ally).ThePWMsignalisampliedbyMOSFET,andtheam-pliedPWMsignalcarri

10、erfrequencyisremovedbyLClow-passlter,therebytheoriginalbasebandaudiosignaldrivespeakerisobtained.Basedonthedifferenceclosed-loopfeedbacktechniqueandthedifferencepre-amp,ahighefciencyPWMCMOSclass-Daudiopoweramplierisproposed,andarail-to-railcomparatorwithwindowfunctionisproposedasPWMcom-parator.Theen

11、tirecircuitissimulatedandveriedbasedonCSMC0.5µmCMOSprocess,andisprovedtobeofhighefciencyandlowpowerconsumption.2.HighefciencyPWMclass-Daudiopoweram-plierSincethatsystemstabilityandnoisecharacteristicoftheclosedloopsystemaremuchbetterthanopenloopsystem9,weemployclosedloopclass-Daudiopowerfrequen

12、cyarchi-tecture,withafeedbacksystem,whichisusedtoreducethedistortion.Consideringtheapplicationwithoutlter,fulldif-ferentialstructureisusedasinputstage,afulldifferentialop-erationalampliercascadedasfulldifferentialintegrator.Theproposedclass-DamplierasshowninFig.1isafullydifferentialamplierwithdiffer

13、entialinputsandoutputs.Thefullydifferentialamplierconsistsofadifferentialampli-erandacommon-modeamplier.Thedifferentialamplierensuresthattheamplieroutputsadifferentialvoltageontheoutputthatisequaltothedifferentialinputtimesthegain.Thecommon-modefeedbackensuresthatthecommon-modeProjectsupportedbytheN

14、ationalOutstandingYoungScientistFoundationofChina(No.60725415),theNationalNaturalScienceFoundationofChina(No.60676009),theDoctorFoundationofMinistryofEducation(No.20050701015),andtheInnovationFunds(No.07C26226101993).Correspondingauthor.Email:zmyhc2009ChineseInstituteofElectronicsReceived23July2008,

15、revisedmanuscriptreceived7October2008025001-1ZhuZhangmingetal.February2009Fig.1.Diagramofclass-Daudiopoweramplier.Fig.2.Diagramofpreamplierandfeedbackcircuit.voltageattheoutputisbiasedaroundVDD/2regardlessofthecommon-modevoltageattheinput.Theproposedclass-Dam-pliercanstillbeusedwithasingle-endedinpu

16、t.However,theproposedclass-Dampliershouldbeusedwithdifferentialin-putswheninanoisyenvironment,likeawirelesshandset,toensuremaximumnoiserejection.Thefullydifferentialamplierallowstheinputstobebi-asedatvoltageotherthanmid-supply.Forexample,ifacodechasamid-supplylowerthanthemid-supplyoftheproposedclass

17、-Damplier,thecommon-modefeedbackcircuitwillad-just,andtheproposedclass-Damplieroutputswillstillbebiasedatmid-supplyoftheproposedclass-Damplier.Theinputsoftheproposedclass-Dampliercanbebiasedfrom0.5toVDD0.8V.Iftheinputsarebiasedoutsideofthatrange,input-couplingcapacitorsarerequired.Thefullydifferenti

18、alamplierdoesnotrequireabypasscapacitor.Thisisbecauseanyshiftinthemid-supplyaffectsbothpositiveandnegativechannelsequallyandcancelsatthedifferentialoutput.GSMhandsetssavepowerbyturningonandshuttingofftheRFtransmitteratarateof217Hz.Thetransmittedsignalispicked-uponinputandoutputtraces.Thefullydiffere

19、ntialampliercancelsthesignalmuchbetterthanthetypicalaudioamplier.Thediagramofclass-DaudiopoweramplierinFig.1mainlyincludesinputcircuit,outputdrivecircuit,logiccontrolunit,deadzonecontrolunit,PWMoscillatormodule,feedbackcircuit,softstartcircuit,turnoffmodule,switchingnoisecon-trolmoduleandsoon.Inputc

20、ircuitisfulldifferentialopera-tionalamplier,tolimitthenoise,increasetheoutputvoltageswing,andincludetheprecedingproportionalamplier,con-nectingthefulldifferentialintegratorconstitutedbyfulldiffer-entialoperationalamplier.PWMoscillatorcircuitgeneratesatrianglewave,andtheprincipleistochargeanddischarg

21、eacapacity,thecurrentofchargeanddischargeisgeneratedbythesamereferencecurrentmirror,forthesamecapacity,thetimeforcharginganddischargingisequal,andsotoformatrianglewave,theoscillatingfrequencyofwhichisdeter-minedbythecapacitanceandcurrent,250kHzinthispaper.PWMmodule,themostsignicantcongurationinclass

22、-Daudioamplier,ismainlycomposedwithtwohysteresiscom-parators,generatessquarewaveswithdifferentdutycyclebycomparisonwithfulldifferenceoftheprecedinginputcircuit.ThefeedbackmoduleadoptingtwoparallelRClters,andthesignalisfedtothedifferentialinputterminaloffulldifferentialintegratorthroughafulldifferent

23、ialoperationalamplier.Fig.3.Fulldifferentialoperationalampliercircuit.3.Pre-ampandfeedbackofclass-DaudiopoweramplierPre-ampandfeedbackofclass-DaudiopoweramplierisshowninFig.2,fulldifferentialoperationalamplierisap-pliedastheinputstage,topre-amplifytheinputdifferenceaudiosignal,anditssingleterminalga

24、inisdeterminedbythevalueofexternalconnectedresistance.Forthebestper-formance,thesingleterminalgainshouldsetbelow2,inthatlowgaincoulddrivethechiptoworkonthebeststate,andthehighinputvoltagemaymaketheinputterminalinsensitivetothenoise.Hence,whentheinputvoltageislow,shouldbepre-ampliedbyanampliedcircuit

25、,insteadofreducingtheresistancetoincreasethecircuitgain.AsshowninFig.2,therststageoftheinputcongura-tionisfulldifferentialproportionalamplier,thesecondstageisfulldifferentialintegrator.ThefeedbackmoduleadoptingtwoparallelRClters,andthesignalisfedtothedifferentialinputendoffulldifferentialintegratort

26、hroughafulldiffer-entialoperationalamplier.So,themostsignicantcongu-rationinclass-Daudioamplierpre-amplierandfeedbacksegmentisfulldifferentialCMOSoperationalamplier.Thefulldifferentialoperationalamplieradoptingthefolded-CascodecongurationandtheinteriorcircuitisshowninFig.3.Thebiasedcircuitandcommon-

27、modecircuitisnotpresentedduetotheextentlimit.M1M3composethein-putstagedifferenceamplier,M3M6composetheoutputstagecircuit,whereM3,M4arethepowersource,M5andM6arecommon-gateamplier,M8andM10composetheactiveloadtransistor,M7andM9composecommon-modefeedback025001-2J.Semicond.30(2)ZhuZhangmingetal.Fig.6.Rai

28、l-to-railcomparatorwithhysteresisfunction.4.PWMrail-to-railcomparatorFig.4.CMOSoperationalamplitude/phase-frequencycharacteristic.Fig.5.Power-supplyrejectionratiocharacteristicofCMOSopera-tionalamplier.circuit,M11andM12areclampingtransistorsusedforreduc-ingtheoperationalampliersettingtime,havingnoef

29、fectonACsmallsignalcharacteristics.AnalyzingthecircuitinFig.3accordingtothesmallsignalmodel,andthevoltagegainisAV=(gmnron)(gmprop)11,(1)1+ronSonN1+ropLwheregmn,ron,gmpandroparethetransconductanceandout-putresistanceofNMOSandPMOS,respectively,andRL,RSarethelimitedoutputresistanceofpowersupply.RNisthe

30、sourceequivalentinputresistanceofNMOS,andRN=1RL(1+),sowecanimprovethelimitedoutputresistancegmpropofpowersupplytoimprovetheDCgainofoperationalam-plier.IftheoutputresistanceoftheloadismuchbiggerthanthatofMOS,themaxgainoffulldifferentialCascodeCMOSoperationalamplierwillbesimpliedasAVmax=2(gmnron)(gmpr

31、op).(2)BasedonBSIM3V3modelofCSMC0.5µmCMOSprocess,PWMcomparatorcharacteristicissimulatedusingHspice,undertheconditionthatpowervoltageVDDis5V,temperatureis25C(roomtemperature).Figure4istheCMOSoperationalamplitude/phase-frequencycharacteristic.Thegreatestopenloopgainis63.7dB,phasemarginis63C,andun

32、itgainbandwidthfrequencyis26.1MHz,whichcanrelaxtheclass-Daudiopoweramplierrequirement.Figure5showsthepower-supplyrejectionratiocharacteristicoffulldifferentialCMOSoperationalamplier.ThePSRRis68.4dB,whichcantotallysatisfythewidepowervoltageapplica-tionrequirementofclass-Daudiopoweramplier.Inordertoim

33、provetheaccuracyandgainofthecom-parator,PWMcomparatorcircuitemploystwo-stageopenloopcomparatorconguration,andforthereasonthatthecomparatorisappliedinaudiocircuit,anoisycircumstance,alsodetectthesignalvariationatthethresholdvalue,generalcomparatorsareinevitabletopresentnoiseattheoutput,thusweaddthehy

34、steresisconguration.M5,M13,M6,M10,M7,M11,andM8,M16inFig.6arecomposedascorrespondinghysteresiscircuit,sotoimprovetheanti-interferenceabilityofcomparator.Asthecomparatorinclass-Daudioamplier,itsoutputmodulationwaveexperiencedaseriesdigitallogicchangetocontrolthepowerMOSFET.Thebestchoiceforthecomparato

35、rcommonmodeoutputtomakeMOSFETworknormallyisVSSVDD,thefullrangeoutput,whichmeansitisnecessaryforthecomparatorcommonmodeinputrangetobeVSSVDD,therefore,wemustadoptrail-to-railstruc-tureasthecomparatorinputstage.ThismentionedstructureisusuallymadeupofaparallelcomplementaryP,Ndifferentialpair,andtheinput

36、stageconguration,composedofNMOSM3,M4andPMOSM1,M2,isshowninFig.6.ThecommonmodeinputrangeforPMOSdifferentialpairisVSS<VCM<VDD|VDS|VGS|,VSS+VDS+VGS<VCM<VDDforNMOSpair,accordingtothesetwoexpressions,thecommonmodeinputrangeforthiscomparatorisVSS<VCM<VDD.ThecommonmodeinputrangeofRail-to-

37、Railarchitec-turecouldbedividedintothreeworkingregions:WhenVCMislow,M1,M2areturnedon,M3,M4areturnedoff,andthebiasedcurrentisprovidedbyIbias1.WhenVCMishigh,M3,M4areturnedon,M1,M2areturnedoff,andthebiasedcur-rentisprovidedbyIbias2.IfVcmisinintermediaterange,thebiasedcurrentisofferedbybothupperandlower

38、tailcurrents,andthenthesumofbiasedcurrentwillbeIbias1+Ibias2.Thein-putstagetotaltrans-conductanceofrail-to-railarchitectureisdeterminedbyID=W1µCox()(VGSVTH)2(1+VDS).2L(3)Ignoringthechannelmodulationeffect(=0),wegetthetotaltrans-conductancethroughderivation:Wgm,total=µnCoxIbias2+µpCoxI

39、bias1.(4)LnLp025001-3ZhuZhangmingetal.February2009Fig.7.ACcharacteristicsofPWMcomparator:(a)DCgain;(b)PSRR.Fig.8.Transientsimulatedresults.Fig.9.Resultsinthecommonmodeinputrange.AccordingtoEq.(4),rail-to-railcircuitregulatestheinputstagetotalbiasedcurrenttorealizethetotaltrans-conductancetobeconstan

40、t,thecomparatorperformanceimproved.Thecomparatoroutputstageadoptsthebasicdifferencestructurewithoutconstant-currentsource,showninFig.6,M19,M20arethedifferentialinput,M18,M17composetheimageload,M20,M17arethetypicalclass-ABoutputar-chitecture,andthereforerealizingrail-to-railvoltageoutput.Atthesametim

41、e,everyMOSinoutputstageischosenasWWWW30µm()17=()18=()19=()20=,whichmeansLLLL1µmtheyarematchingwitheachother,anddothesmallsignalanalysistogetthegainexpressionas()AV=gm19,20rO19,20|rO17,18.(5)BasedonBSIM3V3modelofCSMC0.5µmCMOSprocess,PWMcomparatorcharacteristicissimulatedusingHspice,un-

42、dertheconditionthatpowervoltageVDDis5V,temperatureis25C(roomtemperature).AnalyzingthecircuitwithACmodelTT,SS,FF,thesimulatedresultsisshowninFig.7.ThecomparatorDCgainisshowninFig.7,TT50dB,SS51dB,FF49dB;PSRRinTT,SS,FFis52,47,58dBrespectively,whichindicatesthatprocesserrorhaslittleeffectonPWMcomparator

43、DCopenloopgainandPSRR.TransientsimulatedwaveformisshowninFig.8.Theriseandfalltransfertimedelayofthecomparatoris44and5nsre-spectively,analyzingthecircuitwithTTmodel,andthetotaltimedelayis24.5ns.Thecomparatorpositiveslewrateandnegativeslewrateis360and3600V/µsrespectively.Thesimulatedresultsuggest

44、sthatrisedelayislongerthanfallde-lay.BecauseofthereasonthatM17andM20intheoutputstagehavethesameW/LandthedifferentmobilitybetweenholesinPMOSandelectronicsinNMOSleadingtothediffer-entdrivingabilitybetweenthesetwokindsoftransistors.Thedesignedcomparatorismainlyappliedinaudio,workingun-derlowfrequencyst

45、ate,250kHz.Onthebasisofthesimulatedresults,wecanconcludethat,whenthefrequencyislowthecomparatorisofshortertransferdelay,thequickerresponse.Figure9isthesimulateddccharacteristic,andICMRrangeisfrom0to5V,atthesametimeoutputswingreachesthefullrange.Hence,outputsignalofthecomparatorcanthoroughlydrivethef

46、ollowingaudiologiccircuit,andtherebyensurethedelityoftheaudiosignals.Thecomparatorwaveform,atnormalstate,withsinewave(frequency10kHzandamplitudeintherangeof1.33.7V)andtrianglewave(frequency250kHzandamplitudeintherangeof1.23.8V)astheinputwaves,isshowninFig.10(a).Weinterceptapassageofsimulatedwaveandp

47、resentitsam-plicationinFig.10(b),andtheimaginarylineisthesampledPWMwave.Toavoidthesignaldistortionaftersampling,theamplitudeofsinewaveshouldbelowerthanthatoftrianglewave,andweregulatethegainofpreampliertoavoidoverregulationforthelargeamplitudesignals.Moreover,thelay-outofinputdifferenttransistorspai

48、rshouldbeconsideredtoreducethecomparatoroffsetvoltage.5.DesignresultsanddiscussionBasedonCSMC0.5µmN-wellDPDMCMOSprocess,theproposedhighefciencyclass-Daudiopoweramplierissimulated,siliconveriedandmeasured.Whentheloadistheequivalentloudspeaker8,VDD=3.6V,inputsignalis10kHz025001-4J.Semicond.30(2)P

49、owersupply(V)ZhuZhangmingetal.Table1.Powerandefciencymeasuredresultswithdifferentpowersupplies.Inputsignalfrequency(kHz)Load()THD+N(%)Outputpower(W)Conversionefciency(%)1111114448881.01.01.01.01.01.00.421.062.080.260.591.1975.780.485.883.586.390.1Powersupply(V)Table2.THD+N

50、measuredresultswithdifferentpowersupplies.Inputsignalfrequency(kHz)Load()Outputpower(W)1118880.200.501.00THD+N(%)8Fig.10.OutputwavesofPWMcomparator:(a)Comparatoroutput;(b)Ampliedoutputwaves.Fig.11.Simulatedresultoftheentirecircuit.Fig.12.Micro-photooftheclass-Damp.300mVdifferentialsinewav

51、ewiththephasedifferenceof180C,thesimulatedresultsofclass-Daudiopowerampli-erinthe0.5µmCMOSprocesstypicalmodelispresentedinFig.11,thestabilizedoutputsinewavesignaliscomplete,THD+Nis0.154%.Table1istheoutputpowerandefciencymeasuredre-sultoftheproposedclass-Daudiopoweramplier,withkindsofvoltageandl

52、oad4,8,respectively,andthemaximumconversionefciencyisupto90%,whichistwiceofthatofconventionalclass-ABunderthesamecondition.Table2istheTHD+Nmeasuredresultswithdifferentpowersupplywith8loadand1kHzinputsignal,andtheTHD+Nisless0.20%.Whentheoutputpowerisreachto2.5W,theconversionefciencyisabout85%.Thepowe

53、rsupplyisintherangeof2.55.5V,PSRRisabout75dB.Whenpowersupplyis3.6V,thequiescentcurrentwithnoloadis2.8mAandshutdowncurrentis0.5µA,whichcansatisfythelowpowercondition.Figure12isthemicro-photoofclass-DaudiopoweramplierchipbaseonCSMC0.5µmN-wellDPDMCMOSprocess,andtheeffectiveareais1.47×1.52mm2.Reference5proposeda2.5W,250kHzPWMclass-DaudiopoweramplierbasedonBiCMOSprocesswithpowersupply2.56.5Vandmaximumefciency86%with8load(800mW),whilethevalues2.55.5Vand90%efciencyre-spectivelywithan8load(800mW)fortheproposedclass-Daudiopow

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