英語 電子信息工程ppt課件.ppt

Unit9DigitalSignalProcessing,PassageABasicConceptsofDSPPassageBDigitalSignalProcessorsPassageCComparisonofDSPandASP,PassageABasicConceptsofDSPWedontspeakinadigitalsignal.Adigitalsignalisalanguageof1sand0sthatcanbeprocessedbymathematics.Wespeakinreal-world,analogsignals.Analogsignalsarerealworldsignalsthatweexperienceeveryday-sound,light,temperature,andpressure.Adigitalsignalisanumericalrepresentationoftheanalogsignal.Itmaybeeasierandmorecosteffectivetoprocessthesesignalsinthedigitalworld.Intherealworld,wecanconvertthesesignalsintodigitalsignalsthroughtheanalog-to-digitalconverter,processthesignals,andifneeded,bringthesignalsbackouttotheanalogworldthroughthedigital-to-analogconverter.,1.Theessentialsofanalog-to-digitalanddigital-to-analogconversionThefirstessentialstepinanalog-to-digital(A/D)conversion(asshowninFigure9.1)istosampleananalogsignal.Thisstepisperformedbyasampleandholdcircuit,whichsamplesatregularintervalscalledsamplingintervals.Thelengthofthesamplingintervalisthesameasthesamplingperiod,andthereciprocalofthesamplingperiodisthesamplingfrequencyfs.AccordingtotheNyquisttheorem,asignalwithamaximumfrequencyofWHz(calledaband-limitedsignal)mustbesampledatleast2Wsamplespersecondtoensureaccuraterecording.Whenthisminimumisnotrespected,distortioncalledaliasingoccurs.Aliasingcauseshighfrequencysignalstoappearaslowerfrequencysignals.Tobesurealiasingwillnotoccur,samplingisalwaysprecededbylowpassfiltering.Thelowpassfilter,calledtheanti-aliasingfilter,removesallfrequenciesabovehalftheselectedsamplingrate.,Figure9.1Analog-to-DigitalConversions,Afterabriefacquisitiontime,duringwhichasampleisacquired,thesampleandholdcircuitholdsthesamplesteadyfortheremainderofthesamplinginterval.ThisholdtimeisneededtoallowtimeforanA/Dconvertertogenerateadigitalcodethatbestcorrespondstotheanalogsample.,TheA/Dconverterchoosesaquantizationlevelforeachanalogsample.AnN-bitconverterchoosesamong2Npossiblequantizationlevels.Thelargerthenumberoflevels,thesmallerthequantizationerrors,calculatedasthedifferencebetweenthequantizedlevelandthetruesamplelevel.MostquantizationerrorsarelimitedinsizetohalfaquantizationstepQ.ThequantizationstepsizeiscalculatedasQ=R/2N,whereRisthefullscalerangeoftheanalogsignalandNisthenumberofbitsusedbytheconverter.Thestrengthofthesignalcomparedtothatofthequantizationerrorsismeasuredbydynamicrangeandsignal-to-noiseratio.,Adigitalsignalisrepresentedbyasetofverticallineswithcirclesatthetoptomarkthequantizationlevelsselectedforeachsample.ThebitrateforanA/DconverteristheNfs,wherefsisthesamplingrate.Finally,eachdigitalsampleisassignedadigitalcode,whichcompletestheA/Dprocess.Theresultisadigitalbitstream.Itisthiscollectionofdigitalcodesthatisprocessedindigitalsignalprocessing.,Tosummarize,A/Dcomprisesanti-aliasing,sampling,quantizationanddigitization.Oncedigitalsignalprocessingiscomplete,digital-to-analog(D/A)conversion(asshowninFigure9.2)mustoccur.Thisprocessbeginsbyconvertingeachdigitalcodeintoananalogvoltagethatisproportionalinsizetothenumberrepresentedbythecode.Thisvoltageisheldsteadythroughzeroorderholduntilthenextcodeisavailable,onesamplingintervallater.Thiscreatesastaircase-likesignalthatcontainsfrequenciesaboveWHz.Thesesignalsareremovedwithasmoothinglowpassfilter,thelaststepinD/Aconversion.,Figure9.2Digital-to-AnalogConversions,Theimagesofeachfrequencyfpresentinasampledsignalappear,throughsampling,attheinfinitenumberoffrequencieskfsfHz.WhenthesamplingrateislowerthantherequiredNyquistrate,thatisfs2W,imagesofhighfrequencysignalserroneouslyappearinthebaseband(orNyquistrange)duetoaliasing.Whilethisundersamplingisnormallyavoided,itcanbeexploited.Forexample,signalswhosefrequenciesarerestrictedtoanarrowbandofhighfrequenciescanbesampledataratesimilartotwicethewidthofthebandinsteadoftwicethemaximumfrequency.Alloftheimportantsignalcharacteristicscanbededucedfromthecopyofthespectrumthatappearsinthebasebandthroughsampling.Dependingontherelationshipbetweenthesignalfrequenciesandthesamplingrate,spectralinversionmaycausetheshapeofthespectruminthebasebandtobeinvertedfromthetruespectrumofthesignal.1,2.TechnologiesfordigitalsignalprocessingIfauniversalmicroprocessorsolutionexistedwithwhicheverydesigncouldberealized,theelectronicsindustrywouldntbeaverycompetitiveplace.2However,typicallyinmostelectronicdesigns,morethanoneprocessortechnologycanbeusedtoimplementtherequiredfunctions.Thetrickis,ofcourse,tochoosetheonethatbestdeliverstheperformance,size,powerconsumption,features,softwareandtoolstogetthejobdonefast-withoutbreakingthebudget.Afteralmosttwodecadesofdevelopment,digitalsignalprocessorscontinuetotaketheplaceofcompetitiveprocessors.Digitalsignalprocessorsare,afterall,atthecenterofsignalprocessing.,Adigitalsignalprocessor(DSP)isatypeofmicroprocessor-onethatisincrediblyfastandpowerful.ADSPisuniquebecauseitprocessesdatainrealtime.Thisreal-timecapabilitymakesaDSPperfectforapplicationsthatcannottolerateanydelays.Forexample,didyouevertalkonacellphonewheretwopeoplecouldnttalkatonce?Youhadtowaituntiltheotherpersonfinishedtalking.Ifyoubothspokesimultaneously,thesignalwascut-youdidntheartheotherperson.Withtodaysdigitalcellphones,whichuseDSP,youcantalknormally.TheDSPinsidecellphonesprocesssoundssorapidlyyouhearthemasquicklyasyoucanspeak-inrealtime.HerearejustsomeoftheadvantagesofdesigningwithDSPsoverothermicroprocessors:,Single-cyclemultiply-accumulateoperations;Real-timeperformancesimulationandemulation;Flexibility;Reliability;Increasedsystemperformance;Reducedsystemcost.However,therearesomeoftheotheralternativesavailablefordigitalsignalprocessing.HowtheycomparetoDSPs?,TheFPGAAlternativeField-ProgrammableGateArrays(FPGA)havethecapabilityofbeingreconfigurablewithinasystem,whichcanbeabigadvantageinapplicationsthatneedmultipletrialversionswithindevelopment,offeringreasonablyfasttimetomarket.Theyalsooffergreaterrawperformanceperspecificoperationbecauseoftheresultingdedicatedlogiccircuit.However,FPGAsaresignificantlymoreexpensiveandtypicallyhavemuchhigherpowerdissipationthanDSPswithsimilarfunctionality.Assuch,evenwhenFPGAsarethechosenperformancetechnologyindesignssuchaswirelessinfrastructure,DSPsaretypicallyusedinconjunctionwithFPGAstoprovidegreaterflexibility,betterprice/performanceratios,andlowersystempower.,TheASICAlternativeApplication-specificICs(ASIC)canbetailoredtoperformspecificfunctionsextremelywell,andcanbemadequitepowerefficient.However,sinceASICSarenotfield-programmable,theirfunctionalitycannotbeiterativelychangedorupdatedwhileinproductdevelopment.Assuch,everynewversionoftheproductrequiresaredesignandtripsthroughthefoundry,anexpensiveproposition,andanimpedimenttorapidtime-to-market.3ProgrammableDSPs,ontheotherhand,canbeupdatedwithoutchangingthesilicon,merelychangethesoftwareprogram,greatlyreducingdevelopmentcosts,andavailingaftermarketfeatureenhancementswithmerecodedownloads.Consequently,moreoftenthannot,whenyouseeASICsinrealtimesignalprocessingapplications,theyaretypicallyemployedasbusinterfaces,gluelogic,and/orfunctionalacceleratorsforaprogrammableDSP-basedsystem.,TheGPPAlternativeIncontrasttoASICsthatareoptimizedforspecificfunctions,general-purposemicroprocessors(GPPs)arebestsuitedforperformingabroadarrayoftasks.However,forapplicationsinwhichtheendproductmustprocessanswersinrealtime,ormustdosowhilepoweredbyconsumerbatteries,GPPscomparativelypoorrealtimeperformanceandhighpowerconsumptionallbutrulesthemout.4Moreandmore,theseprocessorsarebeingseenasthedinosaursoftheindustry,tooencumberedwithPCcompatibilityanddesktopfeaturestoadapttothechangingrealtimemarketplace.Astheworldembracestinyhand-heldwireless-enabledproductsthatrequirepowerdissipationmeasuredinmilliwatts-notthewattsthattheseprocessorsconsume-DSPsaretheprogrammabletechnologyofchoice.ThattrendisboundtocontinueasdigitalInternetappliancesgetsmaller,fasterandmoreportable.,Notes1Dependingontherelationshipbetweenthesignalfrequenciesandthesamplingrate,spectralinversionmaycausetheshapeofthespectruminthebasebandtobeinvertedfromthetruespectrumofthesignal.根據(jù)信號頻率和采樣頻率之間的關(guān)系的不同,可能出現(xiàn)“頻譜反轉(zhuǎn)”現(xiàn)象基帶頻譜的形狀和信號真實頻譜的形狀正好相反。beinvertedfrom.和相反。所謂基帶是指不加任何調(diào)制過程的數(shù)字信號傳輸?；鶐捜坑脕韨魉蛿?shù)字脈沖信號,并可以通過時分復(fù)用的方式進(jìn)行多路數(shù)字信號的傳輸。,2Ifauniversalmicroprocessorsolutionexistedwithwhicheverydesigncouldrealized,theelectronicsindustrywouldntbeaverycompetitiveplace.假如存在可用以實現(xiàn)任何設(shè)計的通用微處理器的話,電子行業(yè)就不會競爭得如此激烈了。本句為虛擬語氣。,3Assuch,everynewversionoftheproductrequiresaredesignandtripsthroughthefoundry,anexpensiveproposition,andanimpedimenttorapidtime-to-market.而且,每次推出一個新產(chǎn)品都需要重新設(shè)計并經(jīng)歷所有制造流程。這樣做不但造價昂貴,而且不利于迅速上市。time-to-market的意思為“上市時間”。foundry是指為第三方制造芯片的半導(dǎo)體制造商,可以指那些出售其富余生產(chǎn)能力的大型芯片制造企業(yè),也可以是指專為其他公司制造芯片的企業(yè)。,4However,forapplicationsinwhichtheendproductmustprocessanswersinrealtime,ormustdosowhilepoweredbyconsumerbatteries,GPPscomparativelypoorrealtimeperformanceandhighpowerconsumptionallbutrulesthemout.然而,在最終產(chǎn)品必須實時響應(yīng)的應(yīng)用中,或者必須在電池供電下實現(xiàn)實時響應(yīng)的應(yīng)用中,由于GPP實時性能較差、功耗大，因此就被排除在外了。allbut此處作rulethemout的狀語,涵義為“幾乎,差一點(diǎn)”。ruleout的意思是“將排除在外”。,Exercises1.Fillintheblanks.(1)Thefirstessentialstepinconversionistosampleananalogsignal.(2)Thelengthoftheisthesameasthe,andthereciprocalofthesamplingperiodisthesamplingfrequencyfs.(3)Tosummarize,A/Dcomprises,and.(4)Aisatypeofmicroprocessor-onethatisincrediblyfastandpowerful.,(5)IncontrasttoASICsthatareoptimizedforspecificfunctions,arebestsuitedforperformingabroadarrayoftasks.(6)havethecapabilityofbeingreconfigurablewithinasystem,whichcanbeabigadvantageinapplicationsthatneedmultipletrialversionswithindevelopment,offeringreasonablyfasttimetomarket.,2.TranslatethefollowingparagraphintoChinese.Thefirststepinconvertingananalogsignalissampling.Thisstepisaccomplishedusingasampleandholdcircuit,whichgrabsasamplefromthesignalandholdsitsteadyuntilthenextsamplingtime.Samplesarenormallycollectedatregulartimeintervals,calledsamplingperiods.Iftherateofthesamplingisnotadequate,distortioncalledaliasingcanoccur.TheoutputfromthesampleandholdcircuitispassedtoanA/Dconverter,whichchoosesaquantizationlevelthatisclosesttotheactualamplitudeofthesignal.ThisisthesecondstepinA/Dconversion.Thenumberoflevelstochoosefromdependsonthenumberofbitsusedbytheconverter:forNbits,2Nlevelsarepossible.Sinceanalogamplitudescannotingeneralberepresentedperfectlyinadigitalsystem,quantizationerrorsoccur.,3.TranslatethefollowingsentencesintoEnglish.(1)數(shù)字信號處理是無數(shù)家用和商用系統(tǒng)中的關(guān)鍵部分,其應(yīng)用領(lǐng)域與日俱增。因此,DSP正在成為技術(shù)專家和工程師專業(yè)知識的一個重要組成部分。(2)數(shù)字信號處理可分為定點(diǎn)和浮點(diǎn)兩大類。定點(diǎn)和浮點(diǎn)指的是器件內(nèi)用于存儲和操作數(shù)據(jù)的格式。定點(diǎn)數(shù)字信號處理通常用最少16位來表示每個數(shù)據(jù),典型的浮點(diǎn)數(shù)字信號處理器用最少32位來存儲每個數(shù)據(jù)。(3)和其他科學(xué)和工程應(yīng)用一樣,數(shù)字信號處理器通常使用匯編語言或者C語言進(jìn)行編程。然而,DSP程序和傳統(tǒng)軟件任務(wù)不同。首先,程序通常短得多,如100行而不是1萬行。其次,執(zhí)行速度往往是其應(yīng)用的關(guān)鍵部分。,PassageBDigitalSignalProcessorsDigitalsignalprocessingtaskscanbeperformedbyallprocessors.Specializeddigitalsignalprocessors(DSPs),however,performthesetasksmostefficientlyandmostquickly.WhiletraditionalprocessorsfollowtheVonNeumannarchitecturemodel(asshowninFigure9.3),whichassumesasharedsinglememorytobeusedforbothprograminstructionsanddata,DSPsusetheHarvardormodifiedHarvardarchitecture(asshowninFigure9.4),whichincludesmultipleprogramanddatamemories,alongwithmultiplebusestoaccessthem.1Thisarrangementmeansthatmuchlesswaitingisrequiredwheninstructionsor,numbersarefetchedfrommemory.Infactatleastoneofeachcanbefetchedsimultaneously.Suchoverlappingoftasksiscalledpipelining.Inadditiontomultiplememoriesandbuses,allDSPshavefastmultipliers,accumulators,andshifters,andmanyhavehardwaresupportforcircularbuffers.Addressgeneratorscanspeedupaccessestomemorylocationsreferencedbyregisters.,Figure9.3VonNeumannArchitecture,Figure9.4HarvardArchitecture,DSPsareavailableintwomajorclasses:fixedpointandfloatingpoint.Thefixedpointclassrepresentsrealnumbersinafixednumberofbits.Thepositionofthebinarypoint(similartothedecimalpoint)canbecontrolledbytheprogrammer,anddeterminestherangeofnumbersthatcanberepresented.Astherangeincreases,though,theavailableprecisiongoesdown,sincefewerbitslietotherightofthebinarypoint.In16bits,theformats16.0,15.1,14.2,13.3,12.4,11.5,10.6,9.7,8.8,7.9,6.10,5.11,4.12,3.13,2.14,and1.15arepossible.Thedynamicrange,calculatedas20log(FullScaleRange/SmallestResolvableDifference),remainsthesameforall16-bitformats,20log216=96.3dB.,FloatingpointDSPsrepresentrealnumbersusingamantissaandanexponent,similartoscientificnotation:Manycombinemantissaandexponentintoa32-bitnumber.Thedynamicrangeforfloatingpointdevicesiscalculatedfromthelargestandsmallestmultipliers2E,whereEistheexponent.Thus,forarepresentationthatuses24bitsforthemantissaand8bitsforthesignedexponent,thedynamicrangeis20lg(2127/2-128)=1535.3dB.Alargedynamicrangemeansthesystemhasgreatpowertorepresentawiderangeofinputsignals,fromverysmalltoverylarge.,AssemblylanguageisthecommandlanguageforDSPs.DSPsoftenhavespecializedinstructionsthatmakeprogrammingforcommonDSPtasksmoreconvenientandmoreefficient.Forexample,mostDSPsoffermulti-functioninstructionsthatexploittheirparallelarchitecture.Otherconstructsthatarefrequentlyofferedareefficientloopingschemes,sincesomanyDSPoperationsinvolveagreatdealofrepetition.,ChoosingaDSPforaparticularapplicationisnotalwayseasy.Thefirstdecisionisonwhethertochooseafixedpointorafloatingpointdevice.2Generally,fixedpointdevicesarecheaperandquicker,butfloatingpointdevicesaremoreconvenienttoprogramandmoresuitedtocalculation-intensivealgorithms.Second,thedatawidthoftheDSPdetermineshowaccuratelyitcanrepresentnumbers.Speedisanotherissue,notonlyhowmanycyclesoccurineachsecond,butalsohowmanyinstructionsexecuteineachcycleandhowmuchworkeachoftheseinstructionsaccomplishes.OnewaytoassesstheminimumrequirementsfortheDSPistoestimatehowmanyinstructionsmustbeexecutedforeachreceivedsample.Whenthisnumberismultipliedbythesamplingfrequency,theminimumrequirednumberofinstructionspersecondisobtained.,ThespecifichardwareandsoftwarefeaturesofferedbyaparticularDSPcanmakeonechoicebetterthananother,ascantheamountofon-chipmemoryavailable.SometimesDSPsarechosenbecausewell-matchedsupportinghardware,particularlyA/DandD/Aconverters,isobtainable.Frequently,thequalityandconvenienceofthesoftwaretools,forbothlowlevelandhighlevelprogramminglanguages,arealsomajorfactors,asistheavailabilityofthirdpartysoftware.Asalways,costisafactor.Infact,quiteoften,theDSPthatisfastestandoffersthemostfeatures,butalsofitsthebudget,istheoneselected.,DSPscanbepurchasedinthreeforms,asacore,asaprocessor,andasaboardlevelproduct.InDSP,theterm“core”referstothesectionoftheprocessorwherethekeytasksarecarriedout,includingthedataregisters,multiplier,ALU,addressgenerator,andprogramsequencer.Acompleteprocessorrequirescombiningthecorewithmemoryandinterfacestotheoutsideworld.Whilethecoreandtheseperipheralsectionsaredesignedseparately,theywillbefabricatedonthesamepieceofsilicon,makingtheprocessorasingleintegratedcircuit.,SupposeyoubuildcellulartelephonesandwanttoincludeaDSPinthedesign.YouwillprobablywanttopurchasetheDSPasaprocessor,thatis,anintegratedcircuitthatcontainsthecore,memoryandotherinternalfeatures.ToincorporatethisICinyourproduct,youhavetodesignaprintedcircuitboardwhereitwillbesolderedinnexttoyourotherelectronics.ThisisthemostcommonwaythatDSPsareused.,Now,supposethecompanyyouworkformanufacturesitsownintegratedcircuits.Inthiscase,youmightnotwanttheentireprocessor,justthedesignofthecore.Aftercompletingtheappropriatelicensingagreement,youcanstartmakingchipsthatarehighlycustomizedtoyourparticularapplication.Thisgivesyoutheflexibilityofselectinghowmuchmemoryisincluded,howthechipreceivesandtransmitsdata,howitispackaged,andsoon.CustomdevicesofthistypeareanincreasinglyimportantsegmentoftheDSPmarketplace.,ThereareseveraldozencompaniesthatwillsellyouDSPsalreadymountedonaprintedcircuitboard.ThesehavesuchfeaturesasyourDSPsalreadymountedonaextramemory,A/DandD/Aconverters,EPROMsockets,multipleprocessorsonthesameboard,andsoon.Whilesomeoftheseboardsareintendedtobeusedasstandalonecomputers,mostareconfiguredtobepluggedintoahost,suchasapersonalcomputer.CompaniesthatmakethesetypesofboardsarecalledThirdPartyDevelopers.ThebestwaytofindthemistoaskthemanufactureroftheDSPyouwanttouse.LookattheDSPmanufacturerswebsite;ifyoudontfindalistthere,sendthemane-mail.Theywillbemorethanhappytotellyouwhoareusingtheirproductsandhowtocontactthem.,KeepinmindthatthedistinctionbetweenDSPsandothermicroprocessorsisnotalwaysaclearline.Forinstance,lookathowInteldescribestheMMXtechnologyadditiontoitsPentiumprocessor:“Intelengineershaveadded57powerfulnewinstructionsspecificallydesignedtomanipulateandprocessvideo,audioandgraphicaldataefficiently.Theseinstructionsareorientedtothehighlyparallel,repetitivesequencesoftenfoundinmultimediaoperations.”Inthefuture,wewillundoubtedlyseemoreDSP-likefunctionsmergedintotraditionalmicroprocessorsandmicrocontrollers.TheInternetandothermultimediaapplicationsareastrongdrivingforceforthesechanges.Theseapplicationsareexpandingsorapidly,intwentyyearsitisverypossiblethatthedigitalsignalprocessormaybethe“traditional”microprocessor.,Notes1WhiletraditionalprocessorsfollowtheVonNeumannarchitecturemodel,whichassumesasharedsinglememorytobeusedforbothprograminstructionsanddata,DSPsusetheHarvardormodifiedHarvardarchitecture,whichincludesmultipleprogramanddatamemories,alongwithmultiplebusestoaccessthem.傳統(tǒng)的處理器遵循馮諾依曼模型,該模型采用一個單一的共享存儲器,同時存儲程序指令和數(shù)據(jù);而數(shù)字信號處理器使用的是哈佛結(jié)構(gòu)或改進(jìn)的哈佛結(jié)構(gòu),該結(jié)構(gòu)包含多個程序和數(shù)據(jù)存儲器以及訪問這些存儲器的多套總線。,“馮諾依曼結(jié)構(gòu)”取名自美國杰出的數(shù)學(xué)家約翰馮諾依曼(JohnVonNeumann,1903-1957)。他引導(dǎo)了20世紀(jì)初許多重大數(shù)學(xué)發(fā)現(xiàn)。他的主要成就包括:提出了存儲程序計算機(jī)(storedprogramcomputer)的概念、對量子力學(xué)的數(shù)學(xué)公式化及在原子彈方面的工作?！肮鸾Y(jié)構(gòu)”取名自20世紀(jì)40年代HowardAiken(1900-1973)領(lǐng)導(dǎo)的在哈佛大學(xué)(HarvardUniversity)做的研究工作。,2Thefirstdecisionisonwhethertochooseafixedpointorafloatingpointdevice.首先要決定的是選擇定點(diǎn)器件還是浮點(diǎn)器件。定點(diǎn)和浮點(diǎn)指的是器件內(nèi)用于存儲和操作數(shù)據(jù)的格式。通常，定點(diǎn)數(shù)字信號處理最少用16位來表示每個數(shù)據(jù),典型的浮點(diǎn)數(shù)字信號處理器最少用32位來存儲每個數(shù)據(jù)。,Exercises1.Fillintheblanks.(1)Thefirstdecisionisonwhethertochooseapointorapointdevice.(2)ThespecifichardwareandsoftwarefeaturesofferedbyaparticularDSPcanmakeonechoicebetterthananother,ascantheamountofavailable.(3)SometimesDSPsarechosenbecausesupportinghardware,particularlyA/DandD/Aconverters,isobtainable.(4)DSPscanbepurchasedinthreeforms,and.,(5)Companiesthatmakethesetypesofboardsarecalled.(6)Acompleteprocessorrequirescombiningthecorewithandt