电子信息工程专业英语教程（第5版） 试题与答案 题库5.0

PAGEPAGE1《电子信息工程专业英语教程(第5版)》题库TOC\o"1-3"\uSectionA术语互译 1SectionB段落翻译 5SectionC阅读理解素材 12C.1HistoryofTablets 12C.2ABriefHistoryofsatellitecommunication 13C.3Smartphones 14C.4Analog,DigitalandHDTV 14C.5SoC 15SectionA术语互译课文核心专业术语1transistor晶体管semiconductor半导体LSILarge-scaleIntegration大规模集成（电路）VLSIVeryLarge-scaleIntegration超大规模集成（电路）2register寄存器cache高速缓存capacitor电容器flipflop触发器interfacecircuitry接口电路CMOSComplementaryMetal-OxideSemiconductor互补金属氧化物半导体ECLEmitterCoupledLogic射极耦合逻辑3latch锁存器buffer缓存器bootsector引导扇区assemblylanguage汇编语言BIOSBasicInputOutputSystem基本输入输出系统MIPSMillionInstructionsPerSecond每秒百万条指令4comparator比较器oscillator振荡器currentsource电流源voltagesource电压源levelshifter电平移动器signalconditioner信号调理器5angularfrequency角频率qualityfactor品质因数DCDirectCurrent直流电ACAlternatingCurrent交流电6decimation抽取interpolation插值referencevoltage参考电压successiveapproximation逐次逼近法7inductor电感器rectifier整流器regulator稳压器conductivity导电性linearregulator线性稳压器loadcurrent负载电流8oscillator振荡器detector检波器seriesresonant串联谐振parallelresonant并联谐振phasedetector鉴相器,相位检测器frequencydetector鉴频器,频率检测器VCOVoltageControlledOscillator压控振荡器PLLPhaseLockedLoop锁相环9pad焊盘lead引线powerloss功率损耗frequencyresponse频率响应motherboard主板，母板daughterboard插件板，子板VSWRVoltageStandingWaveRatio电压驻波比10antenna天线basestation基站endoffice端局FCCFederalCommunicationsCommission联邦通信委员会PSTNPublicSwitchedTelephoneNetwork公共交换电话网11vocoder声码器simplex单工，单向通信deltamodulation增量调制spreadspectrumcommunication扩频通信TDMTimeDivisionMultiplexing时分复用FDMFrequency-divisionmultiplexing频分复用12modem调制解调器ethernet以太网powersupply电源heatsink散热片USBUniversalSerialBus通用串行总线HDMIHigh-DefinitionMultimediaInterface高清晰度多媒体接口POSTpower-onself-test开机自检OSOperatingSystem操作系统13schematic原理图embeddedsystem嵌入式系统designflow设计流程presentstate现态nextstate次态EDAElectronicDesignAutomation电子设计自动化HDLHardwareDescriptionLanguage硬件描述语言ASICApplicationSpecificIntegratedCircuit专用集成电路FPGAFieldProgrammableGateArray现场可编程门阵列14prototype样机cryptography密码学statemachine状态机Pmicroprocessor微处理器SoCSystem-on-Chip片上系统15stimulus激励源timing时序highimpedance高阻16aliasing混叠spectrum频谱sampleandholdcircuit采样保持电路anti-aliasingfilter抗混叠滤波器fullscalerange满量程范围dynamicrange动态范围DSPDigitalSignalProcessor数字信号处理器GPPGeneralPurposeProcessor通用处理器17multiplier乘法器accumulator累加器VonNeumannarchitecture冯•诺依曼结构Harvardarchitecture哈佛结构18filtering滤波crystal晶体passband通带stopband阻带voltagereference参考电压cutofffrequency截止频率ADCAnalogtoDigitalConverter模数转换器DACDigitaltoAnalogConverter数模转换器MIPSMillionInstructionsPerSecond每秒百万条指令数SPSSamplePerSecond每秒样本数19blockdiagram框图datarate数据率Reed-Solomoncoding里德-索罗蒙编码（RS编码）Besselfilter贝塞耳滤波器20oscilloscope示波器transmissionbandwidth传输带宽MPEGMotionPictureExpertsGroup运动图象专家组21handoff越区切换baud波特videoconference视频会议networkoperator网络运营商chiprate码片速率timeslot时隙ADSLAsymmetricalDigitalSubscriberLoop非对称数字用户线DSSSDirectSequenceSpreadSpectrum直序扩频22edgedetection边缘检测objectrecognition目标识别magnitudespectrum幅度谱phasespectrum相位谱DCTDiscreteCosineTransform离散余弦变换23resolution分辨率CCDChargeCoupledDevice电荷耦合器件LCDLiquidCrystalDisplay液晶显示器24luminance亮度chrominance色度carrierwave载波25RISCReducedInstruction-SetComputer精简指令集计算机JTAGJointTestActionGroup联合测试行动组26operand操作数thread线程concurrentprocess并发进程truthtable真值表programcounter程序计数器addressingmode寻址模式RTOSReal-TimeOperatingSystem实时操作系统27algorithm算法devicedriver设备驱动程序28oscilloscope示波器multiplexer多路复用器logicanalyzer逻辑分析仪stimulussignal激励信号AWGArbitraryWaveformGenerator任意波形发生器DMMdigitalmultimeter数字多用表29transducer传感器attenuator衰减器electronbeam电子束fundamentalfrequency基频CRTCathodeRayTube阴极射线管30probe探头timingdiagram时序图propagationdelay传输延迟SUTSystemUnderTest被测系统SectionB段落翻译编号m.n代表第m课第n段；此外，a代表前半段，b代表后半段编号中英文对照1.2Theadvantagesofthetransistoroverthevacuumtubewereenormous.Comparedtotheoldtechnology,transistorsweremuchsmaller,faster,andcheapertomanufacture.Theywerealsofarmorereliableandusedmuchlesspower.Thetransistoriswhatstartedtheevolutionofthemoderncomputerindustryinmotion.和真空管相比，晶体管具备巨大的优势——尺寸小、速度快、成本低，性能更可靠、耗能也更少。晶体管的发明带来了计算机工业的蓬勃发展。1.5Bycarefulchemicalcompositionandarrangement,itispossibletocreateaverysmalltransistordirectlyonalayerofsilicon,usingvarioustechnologiestomanipulatethematerialintothecorrectform.Thesetransistorsaresmall,fastandreliable,anduserelativelylittlepower.通过精密的化学合成和设计、运用多种材料处理技术，可以在硅层上直接构造极小的晶体管。这种晶体管体积小、速度快、功能可靠，耗能也少。2.1Memoriescanbemadeinmechanical,magnetic,optical,biologicalandelectronictechnologies.Examplesofmagneticmemoriesaretapes,floppydisks,harddrivesandferroelectricRAMs.ExamplesofopticalmemoriesareCD-ROMs,rewritableCDs.Electronicmemoryisusedextensivelyincomputerequipmentsinceitisthefastestavailable.制造存储器件，可采用机械技术、磁技术、光技术、生物技术和电子技术。软盘、硬盘和铁电随机存储器属于磁存储器件。光存储器件有只读光盘、可写光盘。在计算机设备中，广泛使用的是电子存储器件，因为它是当前速度最快的存储器件。2.5SRAMcomesinmanyspeedclasses,rangingfromseveralnsforcacheapplicationsto200nsforlowpowerapplications.SRAMexistsinbothbipolarandMOStechnology.CMOS[3]technologyboaststhehighestdensityandthelowestpowerconsumption.FastcachememorycanbeconstructedinBiCMOStechnology,ahybridtechnologythatusesbipolartransistorsforextradrive.ThefastestSRAMmemoriesareavailableinECL(EmitterCoupledLogic)bipolartechnology.Becauseofthehighpowerconsumption,thememorysizeislimitedinthistechnology.SRAM的速度等级很多：从高速缓存的几个纳秒到低速应用的200ns。双极性SRAM和MOSSRAM现在都有。CMOS技术的优势在于密度最高、功耗最低。高速缓存可以使用BiCMOS技术构建；BiCMOS是一种混合技术，它使用双极性晶体管作为附加的驱动。采用“射极耦合逻辑”（ECL）双极性技术的SRAM具有最快的速度。由于这种技术的功耗高，所以存储器容量受到限制。2.10TheadvantageofROMisthatitcanbemanufacturedatthelowestpriceinhighvolumes.Anotheradvantageinsomeapplicationsisthatitisimpossibletoalterthedataoncethechipsaremade,andthatnofurtherprogrammingandtestingarerequired.Ontheotherhand,ifthedataorcodemustbechangedthiscanbeasmalldisaster.Therestofthechipswillendinthedustbinandnewchipswillhavetobemade.ROM的优点是量产价格最低。对于某些应用来说，ROM还具备另外一个优点——当芯片制造出来后，其中的数据就不能再改了，也就不需要进一步编程、测试了。但是，假如数据或代码非改不可的话，那么采用ROM就是大错特错。剩余的ROM芯片只好丢进垃圾桶，还得重新制造芯片。3.14ROMstandsforread-onlymemory.AROMchipisprogrammedwithapermanentcollectionofpre-setbytes.TheaddressbustellstheROMchipwhichbytetogetandplaceonthedatabus.WhentheRDlinechangesstate,theROMchippresentstheselectedbyteontothedatabus.ROM是指“只读存储器”。ROM芯片是用一组预设字节编程得到的。地址总线告知ROM芯片要将哪个字节取出并置于数据总线上。当RD信号线改变状态时，ROM芯片将选中的字节输出到数据总线上。3.15RAMstandsforrandom-accessmemory.RAMcontainsbytesofinformation,andthemicroprocessorcanreadorwritetothosebytesdependingonwhethertheRDorWRlineissignaled.Oneproblemwithtoday'sRAMchipsisthattheyforgeteverythingoncethepowergoesoff.ThatiswhythecomputerneedsROM.RAM是指“随机存取存储器”。RAM中包含着以字节为单位的信息，微处理器能够依据RD/WR信号哪个有效来决定字节的读/写。当前RAM芯片的一个问题是：掉电后，所有保存在RAM上的内容全部丢失。这就是计算机需要ROM的原因。3.21Moretransistorsalsoallowforatechnologycalledpipelining[6].Inapipelinedarchitecture,instructionexecutionoverlaps.Soeventhoughitmighttakefiveclockcyclestoexecuteeachinstruction,therecanbefiveinstructionsinvariousstagesofexecutionsimultaneously.Thatwayitlookslikeoneinstructioncompleteseveryclockcycle.有了更多的晶体管，就可以使用流水线技术。在流水线结构中，指令的执行是重叠的。尽管执行每条指令可能需要5个周期，却可以在不同阶段同时执行5条指令。这样看上去好像每个周期都能完成一条指令。3.22Manymodernprocessorshavemultipleinstructiondecoders,eachwithitsownpipeline.Thisallowsformultipleinstructionstreams,whichmeansthatmorethanoneinstructioncancompleteduringeachclockcycle.Thistechniquecanbequitecomplextoimplement,soittakeslotsoftransistors.许多现代处理器有多个指令译码器，而每个指令译码器都有各自的流水线。这样，就可以实现“多指令流”——在一个周期内完成多条指令。“多指令流”技术实现起来相当复杂，需要使用大量晶体管。4.8aThefirstsignalconditioningopampswereconstructedwithvacuumtubespriortotheintroductionoftransistors,sotheywerelargeandbulky.Duringthe1950s,miniaturevacuumtubesthatworkedfromlowervoltagepowersuppliesenabledthemanufactureofopampsthatshrunktothesizeofabrickusedinhouseconstruction,sotheopampmoduleswerenicknamedbricks.Vacuumtubesizeandcomponentsizedecreaseduntilanopampwasshrunktothesizeofasingleoctalvacuumtube.在晶体管出现前，第一个用于信号调理的运放是用真空管构建的，因此它的体积很大。20世纪50年代，低电压工作的小型真空管使运放的体积缩小到一块砖的大小，因此运放模块有了个绰号“砖块”。真空管和元器件体积不断缩小，直至运放缩至一只八脚真空管的大小。4.8bTransistorswerecommerciallydevelopedinthe1960s,andtheyfurtherreducedopampsizetoseveralcubicinches.Mostoftheseearlyopampsweremadeforspecificapplications,sotheywerenotnecessarilygeneralpurpose.Theearlyopampsservedaspecificpurpose,buteachmanufacturerhaddifferentspecificationsandpackages;hence,therewaslittlesecondsourcingamongtheearlyopamps.在20世纪60年代，晶体管实现了商业开发，这进一步将运放的体积减至几立方英寸。早期运放大多是为特定应用制造的，所以它们不一定通用；早期运放是为某种特定应用服务的，而每个生产商制定的技术指标和封装都各不相同；所以，早期运放几乎都不存在另外的货源。6.2aTheflashconverteroperatesbysimultaneouslypresentingtheinputsignaltoabankof2N–1comparators,whosereferencevoltagesaresetbyaresistorchaintoexactlycorrespondtoallofthepossiblesamplelevelswhichcanberepresentedbytheconverter.Theoutputfromeachcomparator(eithera1ora0)isthenencodedintoanN-bitwordrepresentingtheinputsamplelevel.闪式ADC将输入信号同时置于一列（2N-1个）比较器之前，比较器的参考电压由一组电阻设定，参考电压精确对应于转换器能代表的全部采样电压。比较器的输出（0或1）被编码成N位码字以代表输入采样信号电平。6.2bTheflashconverteristhemostsimple,mostintuitiveandalsothefastestsolutionforADCimplementation.Forlargenumbersofbits(e.g.>14bits),thenumberofresistorsneeded(2N–1)becomesprohibitivelylargeformostpracticalapplications.Also,thepowerconsumptionisconsiderablyhigherthansomeoftheslightlyslowerandmoreexoticsolutions.闪式ADC是最简单、最直观和最快速的ADC实现方案。对于多数实际应用而言，当位数较多时（如大于14位），所需的电阻数量就太大了。与一些速度稍慢、特殊的模数转换方案相比，闪式ADC的功耗明显要高。7.1Everynewelectronicproduct,exceptthosethatarebatterypowered,requiresconvertingoff–line115Vacor230Vacpowertosomedcvoltageforpoweringtheelectronics.Efficientconversionofelectricalpowerisbecomingaprimaryconcerntocompaniesandtosocietyasawhole.Switchingpowersuppliesoffernotonlyhigherefficienciesbutalsooffergreaterflexibilitytothedesigner.Recentadvancesinsemiconductor,magneticandpassivetechnologiesmaketheswitchingpowersupplyanevermorepopularchoiceinthepowerconversionarenatoday.除了电池供电的电子产品外，新型电子产品都需要将115V或230V交流电源转换为直流电源为电路供电。而电能转换效率正在成为业界以及整个社会关注的重点。开关电源不仅提供了较高的转换效率，而且为设计者提供了更大的灵活性。半导体技术、磁器件和无源器件技术的发展使开关电源在当今功率转换的舞台上成为日益流行的选择。8.2ACrystalisabasicpiezoelectricquartzcrystal.Onitsown,itcannotgenerateelectricalclocks.Ithastobeconnectedtoaclockoscillatortogetaclockwaveform.Therearetwokindsofcrystals;SeriesResonant,whichcanbemodeledasahighQseriesL-Ccircuit,andParallelResonant,whichcanbemodeledasahighQparallelL-Ccircuit.Theseriesresonantcrystalhasminimumimpedanceattheresonatingfrequency,whiletheparallelresonantcrystalhasmaximumimpedanceattheresonatingfrequency.晶体是一种基本的压电石英晶体。它本身是不能产生时钟信号的，必须和时钟振荡器连接在一起才能得到时钟波形。晶体有两种：串联谐振晶体（可视作高品质因数的串联LC电路）和并联谐振晶体（可视作高品质因数的并联LC电路）。串联谐振晶体在谐振频率点的阻抗最小，而并联谐振晶体在谐振频率点的阻抗最大。9.2Signalintegrityisdefinedbylossofqualityoftheinputsignal.Ideally,thesignalattheoutputofaninterconnectshouldbeequalinallcharacteristicswiththesignalattheinputoftheinterconnect.Inreality,signaldegradationoccurs.Theusermustdefinewhatlevelofdegradationisacceptableor,alternatively,mustdefineminimumacceptablesignallevelsattheoutput.“信号完整性”是指输入信号的质量损失。在理想情况下，互连部件输出端信号的所有特性和输入端信号完全相同。在实际当中，输出端信号质量会下降。用户必须明确可接受的质量下降程度，或者必须定义输出端信号最小可接受电平。9.3Intoday’sdesigns,withclockratesover100MHzandrisetimescommonly1nsorless,designerscannotignoretheroleinterconnectionsplayinalogicdesign.Interconnecteffectscanplayasignificantpartinthetimingandnoisecharacteristicsofacircuit.Thefasterclockratesandrisetimesincreasebothcapacitiveandinductivecouplingeffects,whichmakescrosstalkproblemsgreater.今天，时钟速率超过100MHz，上升时间通常为1ns以下；设计者不能无视互连部件对逻辑设计的影响。对电路的时序特性和噪声特性，互连部件都有显著的影响。时钟速率和上升时间的加快增加了容性耦合效应和感性耦合效应，这使得串扰问题更加严重。9.6Twotypesofcrosstalkcanbegenerated:backwardcrosstalkandforwardcrosstalk.Backward,alsocallednear-endcrosstalk,ismeasuredatthedrivingendoftheconnectorandrepresentsthesumofthecapacitiveandinductivecoupling.Forward,alsocalledfar-endcrosstalk,ismeasuredatthereceivingendoftheconnectorandrepresentscapacitiveminusinductivecoupling.串扰分成“后向串扰”和“前向串扰”两类。“后向串扰”也叫“近端串扰”，它在连接器的驱动端进行测量，代表了容性耦合和感性耦合之和。“前向串扰”也叫“远端串扰”，它在连接器的接收端进行测量，代表了容性耦合和感性耦合之差。10.1Wirelesstelephonescomeintwobasicvarieties:cordlessphonesandmobilephones(sometimescalledcellphones).Cordlessphonesaredevicesconsistingofabasestationandahandsetsoldasasetforusewithinthehome.Theseareneverusedfornetworking.Mobilephoneshavegonethroughthreedistinctgenerations,withdifferenttechnologies:(1)Analogvoice(2)Digitalvoice(3)Digitalvoiceanddata.无线移动电话分为两大类：无绳电话和移动电话。无绳电话由基站和室内手持设备组成。无绳电话不支持网络传输。移动电话的发展经历了三个时期，各有不同的技术：（1）模拟语音（2）数字语音（3）数字语音和数据。10.Inallmobilephonesystems,ageographicregionisdividedupintocells,whichiswhythedevicesaresometimescalledcellphones.InAMPS,thecellsaretypically10to20kmacross;indigitalsystems,thecellsaresmaller.Eachcellusessomesetoffrequenciesnotusedbyanyofitsneighbors.Thekeyideathatgivescellularsystemsfarmorecapacitythanprevioussystemsistheuseofrelativelysmallcellsandthereuseoftransmissionfrequenciesinnearby(butnotadjacent)cells.在移动电话系统中，地理区域分成一个个蜂窝状的小区。这就是“移动电话”也称作“蜂窝电话”的原因。在AMPS系统中，蜂窝小区的典型大小为10～20km；在数字系统中，蜂窝小区要小一些。每个小区使用一组特定的频率，这组频率在其临近的任何小区都不能使用。使蜂窝系统具备很大容量的关键在于使用了较小的蜂窝小区和在附近（但不是临近的）小区重复使用频率。11.AGSMsystemhas124pairsofsimplexchannels.Eachsimplexchannelis200kHzwideandsupportseightseparateconnectionsonit,usingtimedivisionmultiplexing.Eachcurrentlyactivestationisassignedonetimeslotononechannelpair.Theoretically,992channelscanbesupportedineachcell,butmanyofthemarenotavailable,toavoidfrequencyconflictswithneighbouringcells.GSM系统拥有124对单工信道。每个单工信道带宽为200kHz，并以时分复用的方式提供了8路独立连接。每个正在使用的基站都会分配到频率对上的一个时隙。从理论上讲，每个蜂窝小区可以支持992个信道；但为了避免和邻近蜂窝小区发生频率冲突，许多信道并不能使用。12.2APCisageneral-purposetoolbuiltaroundamicroprocessor.Ithaslotsofdifferentparts-memory,aharddisk,amodem,etc.-thatworktogether."Generalpurpose"meansthatyoucandomanydifferentthingswithaPC.Youcanuseittotypedocuments,sende-mail,browsetheWebandplaygames.PC是一种以微处理器为中心的通用工具。它由存储器、硬盘、调制解调器等很多不同的部件共同构成。所谓“通用”是指使用PC可以做许多不同的事情。既可以用它录入文件，也可以用它发送电子邮件、浏览网页和玩游戏。12.16TheBIOSissoftwarestoredonaflashmemorychip.InaPC,theBIOSisembeddedonthemotherboard.Occasionally,aPCmanufacturerwillreleaseanupdatefortheBIOS,andyoucancarefullyfollowinstructionsto"flashtheBIOS"withtheupdatedsoftware.BIOS是储存在闪存芯片中的软件。闪存芯片嵌在PC的主板上。有时候，PC制造商会发布BIOS更新，你可以按照说明“刷新BIOS”。12.19bThePOSTisasmallcomputerprogramwithintheBIOSthatchecksforhardwarefailures.AsinglebeepafterthePOSTsignalsthateverything'sokay.Otherbeepsequencessignalahardwarefailure,andPCrepairspecialistscomparethesesequenceswithacharttodeterminewhichcomponenthasfailed.POST是BIOS中的硬件故障检测程序。如果一切正常，蜂鸣器就会鸣叫一声。如果蜂鸣器发出其他声响，就说明出现了硬件故障。根据鸣叫情况，PC维修人员对照图表判定哪个部件出现了故障。13.4bTwoHDLsareincommonusagetoday:VerilogandVHDL(VHSICHardwareDescriptionLanguage,whereVHSICstandsforVeryHighSpeedIntegratedCircuit).StandardHDLsareimportantbecausetheycanbeusedbydifferentCADtoolsfromdifferenttoolvendors.InthedaysbeforeVerilogandVHDL,everytoolhaditsownHDL,requiringlaborioustranslationbetweenHDLs,forexample,toverifytheoutputfromasynthesistoolwithanothervendor'ssimulator.Verilog和VHDL（VHSIC硬件描述语言，VHSIC代表超高速集成电路）是两种广泛应用的硬件描述语言。标准化HDL是很重要的，因为标准化语言可以被不同生产商提供的不同CAD工具使用。在Verilog和VHDL出现之前，每个CAD工具都有自己的HDL。在不同HDL之间进行转换（例如，使用其他模拟器来验证某个综合工具的输出）既费时又费力。13.5Thebasicbuildingblocksofdigitalcircuitsaregates.Agateisanelectroniccomponentwithanumberofinputsand,generally,asingleoutput.Theinputsandtheoutputsarenormallyinoneoftwostates:logic0orlogicl.Theselogicvaluesarerepresentedbyvoltages(forinstance,0Vforlogic0and3.3Vforlogic1)orcurrents.Thegateitselfperformsalogicaloperationusingallofitsinputstogeneratetheoutput.门电路是构成数字电路的基本模块。门电路是由几个输入和（通常情况下）一个输出组成的电子器件。在通常情况下，输入和输出是“逻辑0”、“逻辑1”两状态之一。逻辑值可以由电压（例如，0V代表“逻辑0”，3.3V代表“逻辑1”）或电流来表示。门电路利用全部输入实现某种逻辑运算以产生输出。14.3aThe“fieldprogrammable”portionoftheFPGA’snamereferstothefactthatitsprogrammingtakesplace“inthefield”(asopposedtodeviceswhoseinternalfunctionalityishardwiredbythemanufacturer).ThismaymeanthatFPGAsareconfiguredinthelaboratory,oritmayrefertomodifyingthefunctionofadeviceresidentinanelectronicsystemthathasalreadybeendeployedintheoutsideworld.FPGA名称中的“现场可编程”是指研发人员“在现场”对FPGA编程，而不是由芯片制造商以“硬连线”方式实现器件的内部功能。也就是说，可以在实验室对FPGA进行配置，也可以对“已投入使用的”电子系统中的FPGA进行配置。15.2aVHDLisalsoageneral-purposeprogramminglanguage:justashigh-levelprogramminglanguagesallowcomplexdesignconceptstobeexpressedascomputerprograms,VHDLallowsthebehaviorofcomplexelectroniccircuitstobecapturedintoadesignsystemforautomaticcircuitsynthesisorforsystemsimulation.VHDL是一种通用编程语言。和其他高级编程语言一样，VHDL将复杂的设计概念表达为计算机程序；为了实现电路自动综合或系统仿真，VHDL可将复杂电子电路的行为输入到一个设计系统中。16.1bAnalogsignalsarerealworldsignalsthatweexperienceeveryday-sound,light,temperature,andpressure.Adigitalsignalisanumericalrepresentationoftheanalogsignal.Itmaybeeasierandmorecosteffectivetoprocessthesesignalsinthedigitalworld.我们天天遇到的现实世界信号都是模拟信号——如声音、光、温度和压力。数字信号是模拟信号的数值表示。在数字世界里，对这些信号进行处理可能会更容易、成本更低。16.12bADSPisatypeofmicroprocessor-onethatisincrediblyfastandpowerful.Itisuniquebecauseitprocessesdatainrealtime.Thisreal-timecapabilitymakesaDSPperfectforapplicationsthatcannottolerateanydelays.“数字信号处理器”是一种速度极快、功能强大的微处理器。DSP与众不同之处在于它能够实时处理数据。实时处理能力使DSP非常适合于那些不容许任何延迟的应用。17.7DSPscanbepurchasedinthreeforms,asacore,asaprocessor,andasaboardlevelproduct.InDSP,theterm"core"referstothesectionoftheprocessorwherethekeytasksarecarriedout,includingthedataregisters,multiplier,ALU,addressgenerator,andprogramsequencer.Acompleteprocessorrequirescombiningthecorewithmemoryandinterfacestotheoutsideworld.Whilethecoreandtheseperipheralsectionsaredesignedseparately,theywillbefabricatedonthesamepieceofsilicon,makingtheprocessorasingleintegratedcircuit.购买DSPs有三种形式：购买内核、购买处理器和购买板级产品。在DSPs中，内核是指处理器中运行关键任务的部分；它包括数据寄存器、乘法器、算术逻辑单元、地址产生器和程序定序器。一个完整的处理器需要将内核、存储器和外部接口组合起来。尽管内核设计和片内外设设计是分别进行的，但是却被制作在同一片硅片上；这样，处理器就能成为单片集成电路。18.4bItisimpossibletoprocessreal-worldanalogsignalsusingpurelydigitaltechniques,sinceallsensors(microphones,thermocouples,straingages,piezoelectriccrystals,diskdriveheads,etc.)areanalogsensors.Therefore,somesortofsignalconditioningcircuitryisrequiredinordertopreparethesensoroutputforfurthersignalprocessing,whetheritbeanalogordigital.单靠纯数字技术是不能完成处理现实世界模拟信号的任务的，因为所有传感器（话筒、热偶、压力感应器、压电晶体、磁盘驱动器头等）都是模拟的。因此，为了使传感器的输出信号能够进一步地进行信号处理（不论模拟信号处理，还是数字信号处理），就需要某种形式的“信号调理电路”。20.3Perceptualcodingexploitscertainflawsinthehumanauditorysystemtoencodeasignalinsuchawaythatitsoundsthesametoahumanlistener,evenifitlooksquitedifferentonanoscilloscope.Perceptualcodingisbasedonthescienceofpsychoacoustics—howpeopleperceivesound.MP3isbasedonperceptualcoding.知觉编码利用了人类听觉系统的缺陷，采用让人耳听不出来差别的方式对信号进行编码，尽管在示波器上观看重放波形差别很大。知觉编码技术是建立在心理声学基础之上的。心理声学研究的是人类感知声音的方式。MP3建立在知觉编码基础之上。22.1Adigitalimageismadeupofmanyrowsandcolumnsofpixels.Forgrayscaleimages,eachpixelisassignedanumberthatrepresentsthegrayshadeassignedtothatpixel.Thelargerthenumberofpixelsinanimage,andthelargerthenumberofavailablegrayscalelevels,thebettertheresolutionoftheimage.一幅数字图像是由多行多列像素组成的。对灰度图像而言，每个像素被赋予一个代表其灰度级的数字。一幅图像拥有的像素越多，可用灰度级越多，这幅图像的分辨率就越高。22.11bLosslesscompressionmeansthatafileiscompactedwithoutlosinganyinformation,sothatthereconstructedfileisidenticaltotheoriginal.Lossycompressionmeansthatsomeinformationfromtheoriginalfileisirretrievablylost,butgenerallythereconstructedfileisextremelyclosetotheoriginal.无损压缩方法压缩了文件，却没有损失原始文件的任何信息——重建文件和原始文件是完全相同的。有损压缩是指原始文件中的有些信息永远丢失了；不过，重建文件和原始文件非常相近。23.1Justlikeaconventionalcamera,adigitalcamerahasaseriesoflensesthatfocuslighttocreateanimageofascene.Butinsteadoffocusingthislightontoapieceoffilm,itfocusesitontoasemiconductordevicethatrecordslightelectronically.Amicroprocessorthenbreaksthiselectronicinformationdownintodigitaldata.和常规相机一样，数码相机也是通过一组透镜将光线聚集并形成景物的像。不过，数码相机并不将光线聚集在胶片上，而是将光线聚集在半导体器件上，这些半导体器件以电信号的形式存储光信号。然后，微处理器把电信息转换成数字数据。24Standardtelevisionusesaninterlacedformattoreduceflickerinthedisplayedimage.Thismeansthatalltheoddlinesofeachframearetransmittedfirst,followedbytheevenlines.Thegroupofoddlinesiscalledtheoddfield,andthegroupofevenlinesiscalledtheevenfield.Sinceeachframeconsistsoftwofields,thevideosignaltransmits60fieldspersecond.标准电视信号采用交错形式来减少画面的闪烁。也就是说，首先发送一帧画面全部的奇数线，然后发送偶数线。奇数线组被称作“奇数场”，而偶数线组被称为“偶数场”。每一帧由两场组成，因此视频信号每秒发送60场。25.3dModernx86partsandtheirsupportchipsareveryhigh-speeddevicesindensepackages.Itisvirtuallyimpossibletohand-prototypeyourowndesignbasedaroundtheseparts;unlessyouwanttospendmanythousandsofdollarsonequipment,attheveryleastyouwillhavetocontractoutsomeassemblywork.现代x86器件及其支撑芯片都是高密度封装形式的高速器件。实际上，不可能以这种器件为基础手工设计样机；除非您想在设备上投入数万美元，但也不得不将其中某些装配工作承包出去。25.7eSinceARMprovidesreferencedesignsformanydifferentperipheralsaswellasthecoreitself,thereareoftensimilaritiesinperipheralcontrolondifferentARMimplementations,evenfromdifferentvendors.Totakeatrivialexample,codetosenddataoutofaserialportcanusuallybeportedfromoneARMvarianttoanotherwithlittleeffort.ARM不仅提供了处理器内核的参考设计，而且提供了许多不同外设的参考设计；因此，在外设控制方面，不同的ARM实现方案（甚至是来自不同厂商的ARM实现方案）往往具有相似性。举个小例子，通常可以不怎么费力地就把一个用于串口数据发送的代码从一个ARM器件移植到另一个ARM器件。26.2VerilogandVHDLarethemostpopularlanguagesforhardwaredescriptionandmodeling.Eachhardwaredescriptionlanguage(HDL)modelssystemswithdiscrete-eventsemanticsthatignoreidleportionsofthedesignforefficientsimulation.Bothdescribesystemswithstructuralhierarchy:asystemconsistsofblocksthatcontaininstancesofprimitives,otherblocks,orconcurrentprocesses.Inaddition,eachHDLexplicitlylistsconnections.Verilog和VHDL是最常用的硬件描述和建模语言。每一种“硬件描述语言”（HDL）都采用了（为高效仿真而忽略设计空闲部分的）离散事件语法对系统进行建模。这两种语言都使用了具有结构化层次的描述系统——将一个系统分成若干模块。系统模块包含了基本元件实例、其他模块和并发进程。此外，每种HDL将这些连接都明确罗列出来。26.20Manyembeddedsystemsuseareal-timeoperatingsystem(RTOS)tosimulatecon-currencyonasingleprocessor.AnRTOSmanagesmultiplerunningprocesses,eachwritteninasequentiallanguagesuchasC.Theprocessesperformthesystem'scomputationsandtheRTOSschedulesthem.Theschedulingattemptstomeetdeadlinesbydecidingwhichprocessesrunatwhattimesandinwhatorder.许多嵌入式系统使用“实时操作系统”（RTOS）来模拟单片处理器的并发性。RTOS管理多个正在运行的进程，每个进程都是用C语言这样的顺序执行语言编写的。进程完成系统的运算，而RTOS对它们进行调度。为了满足时限要求，调度机制将决定哪个进程何时、以何种顺序执行。27.5Interruptlatencyisthetotallengthoftimefromaninterruptsignalarrivingattheprocessortothestartoftheassociatedinterruptserviceroutine(ISR).Whenaninterruptoccurs,theprocessormusttakeseveralstepsbeforeexecutingtheISR.First,theprocessormustfinishexecutingthecurrentinstruction.Next,theinterrupttypemustberecognized.Thisisdonebythehardwareanddoesnotsloworsuspendtherunningtask.Finally,andonlyifinterruptsareenabled,theCPU’scontextissavedandtheISRassociatedwiththeinterruptisstarted.“中断反应时间”是指从中断信号到达处理器到“中断服务程序”（ISR）开始运行之间的全部时间。当中断出现时，在执行ISR之前，处理器必须完成以下几步。首先，处理器必须停止正在执行的指令。然后，必须辨认中断类型。这是由硬件完成的，不会减慢或挂起正在运行的任务。最后，只有当中断使能、CPU环境设置被保存之后，相关的ISR才会启动执行。28.6Unlessyou’reworkingwithapurelyDCcircuit,yourcircuitislikelytorequiresomekindofACstimulussignalasyouevaluatecomponents,functionalblocks,andsubsystems.Thewaveformfromthesignalsourceemulatesasignalcominginfromtheoutsideworld,suchasasensoroutput.Similarly,itcanbeusedasastand-inforwaveformsthatwillappearinas-yet-unavailablepartsofthecircuitdesign.当对元器件、功能模块和子系统进行验证时，电路中很可能需要某种类型的交流激励源，除非你只使用纯直流电路。信号源输出的波形模拟了来自外部世界的信号（如传感器输出信号）。同样，信号源还可用于替代电路设计中尚未完成部分所产生的波形。29.6Oscilloscopescanbeclassifiedsimilarly–asanaloganddigitaltypes.Formanyapplications,eitherananalogordigitaloscilloscopewilldo.However,eachtypehasuniquecharacteristicsthatmaymakeitmoreorlesssuitableforspecificapplications.Digitaloscilloscopescanbefurtherclassifiedintodigitalstorageoscilloscopes(DSOs),digitalphosphoroscilloscopes(DPOs)andsamplingoscilloscopes.示波器也有类似的分类——模拟示波器和数字示波器。对很多应用而言，二者都可胜任。然而，它们也有各自独特之处；对特定应用而言，这些独特之处可能使之更适用，也可能使之不很适用。数字示波器还可进一步分为“数字存储示波器”（DSO）、“数字荧光示波器”（DPO）和“采样示波器”三类。29.14Incontrasttoananalogoscilloscope,adigitaloscilloscopeusesanADCtoconvertthemeasuredvoltageintodigitalinformation.Itacquiresthewaveformasaseriesofsamples,andstoresthesesamplesuntilitaccumulatesenoughsamplestodescribeawaveform.Thedigitaloscilloscopethenre-assemblesthewaveformfordisplayonthescreen.Digitaloscilloscopescanbeclassifiedintodigitalstorageoscilloscopes(DSOs),digitalphosphoroscilloscopes(DPOs),andsamplingoscilloscopes.与模拟示波器不同，数字示波器采用“模数转换器”（ADC）将被测电压转换为数字信息。数字示波器采集到的波形是一组样本，并将这些样本保存，直至样本数达到足以描述波形的数量。之后，数字示波器将这些样本重新组合、在示波器显示屏上显示。数字示波器可分为“数字存储示波器”（DSO）、“数字荧光示波器”（DPO）和采样示波器。30.8Theimpedanceofthelogicanalyzer’sprobes(capacitance,resistance,andinductance)becomespartoftheoverallloadonthecircuitbeingtested.Allprobesexhibitloadingcharacteristics.ThelogicanalyzerprobeshouldintroduceminimalloadingontheSUT,andprovideanaccuratesignaltothelogicanalyzer.逻辑分析仪探头的阻抗（电容、电阻和电感）会成为整个被测电路负载的一部分。所有探头都会表现出负载特性。逻辑分