文献翻译——无线电路设计简介

第1页外文文献资料INTRODUCTIONTOWIRELESSCIRCUITDESIGN1.1.OVERVIEWWirelesscircuitsarenotthatdifferentfromcommonlyknowntwo-wayradio,television,andbroadcastarrangements.Someofthemrequirehighlinearityinmodulation(TVpicture);someworkviarelaystations(two-wayradio).Therealdifferenceslieinthefactthatthecellsizesaremuchsmaller,andthatinmostcasesweattemptmultiplechanneluse(reuse)usingtime-divisionmultiplex,spreadspectrum,orsomeotherefficientmeansofreducingthebandwidthrequiredforcommunication.Onecanarguethatthewirelesscircuitsincludesimpledevices,suchasgarage-dooropenersandwirelesskeysforautomobiles(wehaveseenmanycaseswherestronginterferingsignalspreventedthecarownersfromreclaimingtheircarsuntiltheinterferingsignaldisappeared).Anotherlongtimefavoriteiscordlesstelephones:initially,50-MHzmodelswithessentiallynoprivacyprotection;later,moresophisticatedmodelsthatoperateat900MHz;andnow,dual-banddesignsthatuse900MHzand2.4GHz.Thelargestwirelessgrowthareaisprobablythecellulartelephones.Thetwomajorapplicationsarethehandsets,commonlyreferredtoascellphonesoroccasionallyas“handies,”andthebasestations.Thebasestationshavemanymoreproblemswithlarge-signal-handlinglinearityathighpower,althoughhandsetusersmayrunintosimilarproblems.Anexampleofthisisthewaitingareaofanairport,wheremanytravelersaretryingtoconductlast-minutebusiness:Inoneinstance,weconcludedthatabout30%ofallthepeoplepresentwereontheair!Itwouldhavebeenfuntoevaluatethisreceiver-hostileenvironmentwithaspectrumanalyzer.romsuchusecomesanxietyfactors,thelesserofwhichis“Whenwillmybatterydie?”asparebatterytendstohelpandthegreaterofwhichtheongoingquestion,“Willthiscell-phonetransmitterharmmybody?”22.Abriefcommentfortheself-proclaimedexpertsinthisarea:A50100-kWTVtransmitter,specificallyitsvideoorpictureportion,connectedtoahigh-gainantenna,emitslevelsofenergyin第2页line-of-sightpathsthatbyfarexceedthepulsedenergyfromacellphone.Specifically,thedurationofenergyissignificantlysmaller,andtheabsoluteenergyismorethanathousandfoldhigher,thantheradiofrequency(R.)supposedlyharmingusfromthecellularphone.Handheldtwo-wayradioshavebeenusedforthelast30yearsorsobypoliceandothersecurityinterests,operatinginthefrequencyrangefrom50to900MHzwithantennasclosetotheusersheads,andtherearenoknowncasesofcanceroranyotherillnessescausedbythesehandheldradios.RecentstudiesinEngland,debatablyornot,showedthatthereaction-timelevelofpeopleusingcellphonesactuallyincreasedbutthentherearealwaystheskepticsandpoliticallymotivatedwhoignorethefacts,trytoinfluencethemedia,andhavetheir15minutesoffame(asAndyWarholusedtosay).Astothe“harmful”radiation,.figure1-1showsthesimulatedradiationofaMotorolaflipphone.Whiletherearenoabsolutevaluesattachedtothepatterncolors,itisinterestingtoseethattheantennaextensioninsidetheplasticcasingalsoradiates,butmostoftheenergydefinitelyisemittedbythetopoftheantenna.Itseemstobeagoodideatoholdthetelephoneinsuchawaythattheantennapointsawayfromthehead,“justincase.”Theuserwillfinda“warm”sensationthatwillhavemoretodowiththeefficiencyoftheR.poweramplifierheatingupthecasethantheeffectofradiation.Withthisintroductioninplace,wewillfirsttakealookatatypicalultra-high-frequencysuper-high-frequency(UH./SH.)transceiverandexplainthepathfromthemicrophonetotheantennaandback.Afterthis,wewillinspecttheradiochannelanditseffectonvariousmethodsofdigitalmodulation.Analysisofwirelessreceiversandtransmitterswillbenext,followedbyalookatavailablebuildingblocksandhowtheyaffecttheoverallsystem.Tovalidatepropersystemoperation,afairlylargenumberofmeasurementsandtestsmustbeperformed,andconveyingtheirpurposeandimportancewillnecessitatethedefinitionofanumberofsystemcharacteristicsandconcepts,suchasdynamicrange.finally,afterthisisdone,wewilllookattheissueofwirelesssystemtesting.Again,weintendtogiveguidanceapplicabletobattery-operated,handheldoperationaswellashigh-poweredbasestations.第3页Figure1-1SimulatedantennaradiationofaMotorolaflipphone.1.2.SYSTEMFUNCTIONSAcellulartelephoneisahybridbetweenadouble-sidebandandfrequency-modulated.M;orphase-modulated(PM)transceiver.Theactualtransmissionisnotcontinuousbutispulsed,andbecauseofthepulsespectrumthereisasignalbandwidthconcernduetokeyingtransients,notunlikeintermodulationproductsofasingle-sideband(SSB)transceiverclutteringupadjacentchannels.Thecellulartelephoneisalsoalineartransceiverinthesensethatitssignal-handlingcircuitrymustbesufficientlyamplitude-andphase-lineartopreservethemodulationcharacteristicsoftheAM/PMhybridemissionsittransmitsandreceives.Containingsuchanemissionsspectralregrowth,whichaffectsoperationonadjacentchannels,isnotunlikethelinearityrequirementsweencounterinSSBtransceiversrequirementssostringentthatamplifiersmustberunnearlyinClassAtomeetthem.Thetime-divisionmultipleaccess(TDMA)operatingmode,whichallowsmanystationstousethesamefrequencythroughtheuseofshort,preciselytimedtransmissions,requiresasystemthattransmitswithasmalldutycycle,puttingmuchlessthermalstressonapoweramplifierthancontinuousoperation.Powermanagement,includingasleepmode,isanotherimportantissueinhandsetdesign.Figure1-2showstheblockdiagramofahandheldtransceiver.Thisisapplicableforcellulartelephonesandothersystemsthatallowfullduplex.orthosenottoofamiliarwithtransceivers,hereisa“walk”throughtheblockdiagram.TheR.第4页signalinterceptedbytheantennaisfedthroughaduplexfilterintoafrontendconsistingofapreamplifier,anadditionalfilter,andamixer.Theduplexerisoptimizedmoreforseparatingtransmitandreceivefrequenciesthanextremeselectivity,butbecauseofthetypicallowfieldstrengthsofincomingsignals,itprovidesenoughselectivitytoguardthereceiverpathagainstoverloadandintermodulationproducts.Thepreamplifieriseitherasingletransistororacascodearrangementwithafilterfollowingit.Thesehigh-bandfilters,mostlysuppliedbyMurata,aretypicallysurfaceacousticwave(SAW)filterswithverysmalldimensions.Wewouldalreadyliketopointoutinthispartoftheblockdiagramthatthesefilterstypicallyhavehigh-impedanceinputsandoutputs(somewherebetween200and1k),thereforeeliminatingthenicetest-setuppossibilitiestypicallyprovidedina50-system.Generally,integratedcircuit(IC)-typemixersalsooperateathighimpedances,whichmakesmatchingeasier.Thefilterfollowingthemixerisresponsibleforreducingtheimage,andthenwegototheintermediatefrequency(I.)anddemodulation.Theparticularchiporchipsmentionedhere,suppliedbyPhilips,aresetoutforadouble-conversionreceiver,andthedemodulationisaccomplishedwithaquadraturedetectorfor.Manalogmodulation.Therestofthecircuitryonthehorizontalpathdoesdigitalsignalprocessing(DSP)andoverallcontrolfunctions.Thefourblocksatthefarrightrefertothecentralprocessor,whichhandlessuchthingsasdisplay,powermanagement,andinformationstorage(suchasfrequentlyusedtelephonenumbers).AniceoverviewaboutDSPin“readable”formisgivenbyKostic1.第5页Figure1-3Thetransmitportionconsistsofanindependentsynthesizerthatismodulated.Therearedualsynthesizerchipsavailabletoaccommodatethis.Bothreceiveandtransmitfrequenciesarecontrolledbyaminiaturetemperature-compensatedcrystaloscillator(TCXO).Oneofitsoutputsisalsousedasthesystemmasterclockforallthedigitalactivities.Theoutputofthevoltage-controlledoscillator(VCO)isthen第6页amplifiedandfedtotheantennathroughthesameduplexfilterasthereceiveportion.Therearealsoschemesavailableforadvancedmodulationmethods,specifically,code-,frequency-,andtime-divisionmultipleaccess(CDMA,.DMA,andTDMA,respectively).Inthesecases,thetransmitterisnotactiveallthetime,andtheduplexercanbereplacedwithadiodeswitchusingaquarter-wavelengthtransmissionlinetogetherwithaPINdiodefortherequiredswitching.Manymoderndevicesuse“zeroI.”ordirectconversion,whichsimplifiestheI.ormodulationportionoftheunitsignificantly.figure1-3showsanAlcatelsingle-chipdirect-conversiontransceiver.Thesignalisfedtoanimage-rejectmixerwiththelocaloscillator(LO)inquadrature,andtheselectivityisobtainedbymanipulatingthe“audiobandwidth.”Todaywehavealargenumberofimplementationsusingdifferentschemesthatarebeyondthescopeofthisbook;therefore,wehavedecidedtolimitourselvestoabasicintroductionbecausemostoftherelevantdemodulationandcodingaredoneinDSP,forwhichwewillgiveappropriatereferences.AniceoverviewofdifferentarchitecturesisfoundinRazavi2.1.3.THERADIOCHANNELANDMODULATIONREQUIREMENTS1.3.1.IntroductionThetransmissionofinformationfromafixedstationtoamobileisconsiderablyinfluencedbythecharacteristicsoftheradiochannel.TheR.signalnotonlyarrivesatthereceivingantennaonthedirectpathbutisnormallyreflectedbynaturalandartificialobstaclesinitsway.Consequentlythesignalarrivesatthereceiverseveraltimesintheformofechoes,whicharesuperimposedonthedirectsignal(figure1-4).Thissuperpositionmaybeanadvantageastheenergyreceivedinthiscaseisgreaterthaninsingle-pathreception.Thisfeatureismadeuseofinthedigitalaudiobroadcasting(DAB)single-frequencynetwork.However,第7页Figure1-4Mobilereceiveraffectedbyfading.thischaracteristicmaybeadisadvantagewhenthedifferentwavescanceleachotherunderunfavorablephaseconditions.Inconventionalcarradioreceptionthiseffectisknownasfading.Itisparticularlyannoyingwhenthevehiclestopsinanareawherethefieldstrengthisreducedbecauseoffading(e.g.,attrafficlights).Additionaldifficultiesarisewhendigitalsignalsaretransmitted.Ifstrongechosignals(comparedtothedirectlyreceivedsignal)arriveatthereceiverwithadelayontheorderofasymbolperiodormore,time-adjacentsymbolsinterferewitheachother.Inaddition,thereceivefrequencymaybefalsifiedathighvehiclespeedsbecauseoftheDopplereffectsothatthereceivermayhaveproblemsinestimatingtheinstantaneousphaseinthecaseofangle-modulatedcarriers.Botheffectsleadtoahighsymbolerrorrateevenifthefieldstrengthissufficientlyhigh.Radiobroadcastingsystemsusingconventionalfrequencymodulationarehardlyaffectedbytheseinterferingeffects.Ifananalogsystemisreplacedbyadigitalonethatisexpectedtoofferadvantagesovertheprevioussystem,ithastobeensuredthattheseadvantagesforexample,betteraudiofrequencysignal/noise(A.S/N)andthepossibilityofsupplementaryservicesforthesubscriberarenotattheexpenseofreceptioninhillyterrainorathighvehiclespeedsbecauseofextremefading.orthisreasonamodulationmethodcombinedwithsuitableerror第8页protectionhastobefoundformobilereceptioninatypicalradiochannel,whichisimmunetofading,echo,andDopplereffects.Withaviewtothis,moredetailedinformationontheradiochannelisrequired.Thechannelcanbedescribedbymeansofamodel.Intheworstcase,whichmaybethecaseforreceptioninbuilt-upareas,itcanbeassumedthatthemobilereceivesthesignalonseveralindirectpathsbutnotonadirectone.Thesignalsarereflected,forexample,bylargebuildings;theresultingsignaldelaysarerelativelylong.Inthevicinityofthereceiverthesepathsaresplitupintoagreatnumberofsubpaths;thedelaysofthesesignalsarerelativelyshort.Thesesignalsmayagainbereflectedbybuildingsbutalsobyothervehiclesornaturalobstaclesliketrees.Assumingthesubpathsarestatisticallyindependentofeachother,thesuperimposedsignalsattheantennainputcauseconsiderabletime-andposition-dependentfield-strengthvariationswithanamplitudeobeyingtheRayleighdistribution.(figures1-5and1-6).Ifadirectpathisreceivedinaddition,thedistributionchangestotheRicedistribution.andfinally,whenthedirectpathbecomesdominant,thedistributionfollowstheGaussiandistributionwiththefieldstrengthofthedirectpathbeingusedasthecentervalue.Figure1-5ReceivesignalasafunctionoftimeorpositionInaRayleighchannelthebiterrorrate(BER)increasesdramaticallycomparedtotheBERinanadditivewhiteGaussiannoise(AWGN)channel(figure1-7).1.3.2.ChannelImpulseResponseThisscenariocanbedemonstratedbymeansofthechannelimpulseresponse.Letsassumethataveryshortpulseofextremelyhighamplitude第9页intheidealcase,aDiracpulse(t)issentbythetransmittingantennaatatimet0=0.Thispulsearrivesatthereceivingantennadirectandintheformofreflectionswithdifferentdelaysianddifferentamplitudesbecauseofpathlosses.Theimpulseresponseoftheradiochannelisthesumofallreceivedpulses(.igure1-8).Sincethemobilereceiverandalsosomeofthereflectingobjectsaremoving,thechannelimpulseresponseisafunctionoftimeandofdelaysi;thatis,itcorrespondstoFigure1-6RayleighandRicedistributionsFigure1-7BERinaRayleighchannel.Thisshowsthatdeltafunctionssentatdifferenttimestcausedifferentreactionsintheradiochannel.Inmanyexperimentalinvestigationsdifferentlandscapemodelswithtypicalechoprofileswerecreated.Themostimportantare：第10页Figure1-8Channelimpulseresponse.Ruralarea(RA)Typicalurbanarea(TU)Badurbanarea(BA)Hillyterrain(HT)Thechannelimpulseresponseinformsonhowthereceivedpowerisdistributedtotheindividualechoes.Aparameter,thedelayspread,canbecalculatedfromthechannelimpulseresponse,permittinganapproximatedescriptionoftypicallandscapemodels(figure1-9).Thedelayspreadalsoroughlyinformsonthemodulationparameters,carrierfrequencysymbolperiod,anddurationofguardinterval,whichhavetobeselectedinrelationtoeachother.Ifthereceiverislocatedinanareawithahighdelayspread(e.g.,inhillyterrain),echoesofthesymbolssentatdifferenttimesaresuperimposedwhenbroadbandmodulationmethodswithashortsymbolperiodareused.InthecaseofDAB,thisproblemis第11页aggravatedbytheuseofsingle-frequencynetworks.Anadjacenttransmitteremittingthesameinformationonthesamefrequencyhastheeffectofanartificialecho(figure1-10).Thishastheconsequencethatrelativelynarrowbandmodulationmethodshavetobeused.Ifthisisnotpossible,channelequalizingisrequired.orchannelequalizing,acontinuousestimationoftheradiochannelisnecessary.Theestimationisperformedwiththeaidofaperiodictransmissionofdataknowntothereceiver.InnetworksaccordingtotheGroupeSpecialeMobile(GSM)standardsamidambleconsistingof26bitsthetrainingsequenceistransmittedwitheveryburst.ThetrainingsequencecorrespondstoacharacteristicpatternofI/Qsignalsthatiskeptinamemoryinthereceiver.Thebasebandsignalsofeveryreceivedtrainingsequencearecorrelatedwiththestoredones.romthiscorrelationthechannelcanbeestimated,andthepropertiesoftheestimatedchannelwillthenbefedtotheequalizer.TheequalizerusestheViterbialgorithm(maximumsequencelikelihoodestimation)fortheestimationofthephases,whichmostlikelyhavebeensentatthesamplingtimes.romthesephasestheinformationbitsarecalculated(figure1-12).Awell-designedequalizerthenwillsuperimposetheenergiesofthesingleechoesconstructively,sothattheresultinanareawheretheechoesarenottoomuchdelayeddelaytimesupto16shavetobeoleratedbyareceiverisbetterthaninanareawithnosignificantechoes.第12页第13页中文翻译稿无线电路设计简介1.1.概述无线电路与从通常已知的双向无线电，电视和广播安排所不同。其中一些需要在调制（电视画面）高线性度;经由中继站（双向无线电）的一些工作。真正的差别在于一个事实，即蜂窝尺寸要小得多，并且在大多数情况下，我们试图多个信道使用（再利用），使用时分多路复用，扩频，或减少通信所需的带宽的一些其他有效手段。人们可以争辩说，无线电路包括简单的设备，如车库开门器和汽车无线钥匙（我们已经看到很多情况下，强干扰信号阻止车主从回收他们的汽车，直到干扰信号消失）。另一个长期最喜欢的是无绳电话：最初，50-MHz型号，基本上没有隐私的保护;后，即在900MHz的运行更复杂的模型，而现在，使用900MHz和2.4GHz双频设计。全球最大的无线增长领域可能是移动电话。两个主要应用是手持设备，通常被称为蜂窝电话或偶尔为基站。基站有更多的问题在高功率的大信号处理的线性度，虽然手机用户可能会遇到类似的问题。这方面的一个例子是等候区的一个机场，在那里许多旅客正在努力进行最后一分钟的业务：在一个实例中，我们得出的结论是大约30所有在场的人都在空中！这本来是有趣的，以评估该接收机恶劣的环境使用频谱分析仪。罗如考虑自带焦虑因素的影响，其中较小的疑问是“我的电池什么时候会用完？”-一块备用电池往往可以帮助更大的正在发生的问题，“请问这个手机发射的辐射会伤害我的身体吗？”。简评在这方面自称专家：一个50-100千瓦电视发射机，特别是其视频或图片部分，连接到一个高增益天线，发射能量的视距路径的水平，由远离手机超过脉冲能量。具体地，能量的持续时间是显著减小，并且绝对能量超过一千倍以上，假想可以从电话伤害我们。手持双向无线电通讯设备已被用于在过去30年左右的警察和其他安全利益，从50到900MHz的天线贴近用户的头部在频率范围内工作，并有癌症没有已知的情况下，或任何其他疾病引起的这些手持对讲机。最近在英国的研究，相对与否，结果显示，使用手机的人的反应时间等级实际上增加了，但后来总有谁无视事实的怀疑和政治动机，试图影响媒体，并把他们的15分钟成名（如安迪沃霍尔曾经说过）。至于“有害”的辐射。图1-1显示了摩托罗拉翻盖手机的模拟辐射。虽然有附着在第14页图案颜色没有绝对的值，这是有趣的是，在塑料外壳内的天线延长也散发，但大部分的能量肯定是由天线的顶端射出。这似乎是一个好主意，握住电话机以这样的方式使天线指向远离头部，“以防万一”。用户会发现一个“热”的感觉，将有更多的是与的效率R.功率放大器升温比辐射的作用的情况。有了这个介绍的地方，我们就先来看看一个典型的超高频超高频（UH/SH）收发器和解释从麦克风到天线和背部的路径。在此之后，我们将检查无线信道及其对数字调制的各种方法的效果。无线接收机和发射机的分析将是下一个，然后看看有积木，以及它们如何影响整个系统。为了验证系统正常运行，必须进行相当大量的测量和试验，并传达他们的目的和重要性，将需要的一些系统特性和概念，如动态范围的定义。最终，之后做到这一点，我们将着眼于无线系统测试的问题。同样，我们打算给适用于电池供电的手持式操作，以及高功率基站的指导。1.2.系统功能一种蜂窝电话是一个双边带和频率调制的混合体M;或相位调制（PM）收发器。实际的传输是不连续的，但是脉冲，并且由于脉冲频谱的有一个信号带宽的问题，由于键控瞬变，而不是不同的单边带（SSB）收发塞满了相邻信道的互调产物。蜂窝电话也是在这个意义上，其信号处理电路必须具有足够的振幅和相位的线性保留AM/PM混合排放它发送和接收的调制特性的线性收发器。含有这些发光的频谱再生，从而影响操作上的相邻信道，是没有什么不同，我们遇到的放大器必须在接近A级运行，以满足他们的线性度要求在SSB收发器，要求非常严格。时分多址（TDMA）的经营模式，这使得许多电视台通过使用短的，精确定时传输使用相同的频率，需要一个系统，有一个小的占空比传输，将少得多的热应力对电源放大器比连续操作。电源管理，包括睡眠模式，是在手机设计的另一个重要问题。图1-2显示了一个手持式收发器的框图。这是适用于移动电话和其他系统允许全双工。，或者那些不太熟悉收发器，这里是一个“走”过框图。由天线截获R.信号通过一个双工滤波器被送入前端包括一个前置放大器，一个额外的滤波器，和一个混频器。双工器进行了优化多为分离发送和接收的频率比极端的选择性，但由于输入信号的典型的低场强的，它提供了足够的选择性，以防止过载和互调产物的接收路径。该前置放大器可以是下列它是单晶体管或带有过滤器的共源共栅结构。这些高带滤波器，大多是由村田制作所提供的，通常表面具有非常小的尺寸声波（SAW）滤波器。我们已经想指出在这部分的框图，这些过滤器通常具有高阻抗输入和输出（介于200和1k）的，因此消除了通常在50所提供的很好的测试设置的可能性-系统。通常，集成电路（IC）的型混合器也工作在高阻抗，这使得更容易匹配。以下混合器中的过滤器是负责降第15页低图像，然后我们到中频和解调。在特定的芯片或芯片在这里所提到的，由飞利浦提供的，载了双转换接收器和解调是通过为：M模拟调制正交检波器。在水平路径上的电路的其余部分做数字信号处理（DSP）和整体控制的功能。在目前的四个街区的权利指的是中央处理器，它处理诸如显示器，电源管理和信息存储（如常用的电话号码）。在“读”的形式对DSP的一个很好的概述了科斯蒂奇给出。发射部分由被调制一个独立的合成。有双合成芯片可用来适应这一点。接收和发送频率由一个微型温度补偿型晶体振荡器（TCXO）的控制。它的一个输出端也被用作系统的主时钟的所有数字活动。电压控制振荡器（VCO）的输出然后被放大，并通过相同的双工滤波器作为接收部分馈送到天线。也有可用于先进的调制方案的方法，具体而言，（CDMA，DMA和TDMA分别）码，频率和时分多址接入。在这些情况下，发射器是不活跃的时候，和双工器可以被替换为使用四分之一波长传输线，连同所需的切换PIN二极管的二极管开关。许多现代化的设备使用“零一”或直接转换，这显著简化了装置的一或调制的部分。图1-3显示了阿尔卡特单芯片直接变频收发器。该信号被馈送到一个镜像抑制混频器，本地振荡器（LO）正交，并且通过操纵所获得的选择性“音频带宽。”今天我们也使用不同的方案，超出的范围的大量的实现这本书，因此，我们决定将自己限制在一个基本的介绍，因为大部分的相干解调和编码都做了DSP，为此我们将给予适当的参考。不同体系结构的一个很好的概述在拉扎维发现。1.3.无线电信道和调制要求1.3