通信工程专业英语PPT课件.ppt

TechnicalEnglish ForInformationScienceandElectronicEngineering 0 1 开场白 好的英语是 读 出来的 学习任何语言都要大量阅读 熟读唐诗三百首 不会作诗也会吟 大凡读得多的人 语言表达能力都比较强 学英语也要大量阅读 英语好的人 一般说来都读过相当数量的书 只有读得多的人才能真正学好英语 很多人热衷于做题目 以为这是学英语的正确途径 做的试题一套又一套 英语水平却并无实质性提高 好的英语是 读 出来的 不是做练习 做 出来的 读 出来的英语是地道的 自然的 因为学的是 语感 做 出来的英语往往流于生硬 因为是依赖 语法规则 硬做的 1 2 开场白 好的英语是 读 出来的 我主张一口气读下去 即便有个别单词挡道 只要不影响整体内容的理解 就不必停下来查词典 因为那样会打断思路 影响阅读速度 甚至扼杀阅读兴趣 阅读主要目的在于语言吸收上的潜移默化 在于获得语感 阅读需要 量 没有大量语言 输入 难以学好英语 国内学习者恰恰语言输入量太少 输出量就更少 往往事倍功半 练习要做 但要适量 重要的是阅读 大量的阅读 节引自 黄源深 英语阅读也轻松 文汇报 2004 8 2 2 UnitOne Electronics AnalogandDigital 3 PartI IdealOperationalAmplifiersandPracticalLimitations 4 5 NewWords 5 6 NewWords 6 7 1 Inordertodiscusstheidealparametersofoperationalamplifiers wemustfirstdefinetheterms andthengoontodescribewhatweregardastheidealvaluesforthoseterms Atfirstsight thespecificationsheetforanoperationalamplifierseemstolistalargenumberofvalues someinstrangeunits someinterrelated andoftenconfusingtothoseunfamiliarwiththesubject 对这些指标项讲述我们所认为的理想值 经常使那些对运放不熟悉的人感到迷惑 7 8 1 Theapproachtosuchasituationistobemethodical andtakethenecessarytimetoreadandunderstandeachdefinitionintheorderthatitislisted Withoutarealappreciationofwhateachmeans thedesignerisdoomedtofailure Theobjectiveistobeabletodesignacircuitfromthebasisofthepublisheddata andknowthatitwillfunctionaspredictedwhentheprototypeisconstructed 1 按照列出的次序阅读并理解每一个定义 能按公布的数据设计电路 并确认构建的样机具有预计的功能 8 9 1 Itisalltooeasywithlinearcircuits whichappearrelativelysimplewhencomparedwithtoday scomplexlogicarrangements toignoredetailedperformanceparameterswhichcandrasticallyreducetheexpectedperformance 2 对于线性电路 它们与现在的复杂逻辑电路结构相比看起来较为简单 因而在设计中 太容易忽视具体的性能参数了 这些 参数 可极大地削弱预期性能 本句主要结构 Itiseasy toignore 9 10 2Anexample Letustakeaverysimplebutstrikingexample Considerarequirementforanamplifierhavingavoltagegainof10at50kHzdrivingintoa10kWload 3Acommonlow cost internallyfrequency compensatedopampischosen ithastherequiredbandwidthataclosed loopgainof10 anditwouldseemtomeetthebill 4Thedeviceisconnected anditisfoundtohavethecorrectgain 考虑对一个50kHz频率时电压增益为10的放大器驱动10kW负载时的要求 注意at和into的用法 看来满足价格要求 bill 帐单 10 11 2 Butitwillonlyproduceafewvoltsoutputswingwhenthedataclearlyshowsthattheoutputshouldbecapableofdrivingtowithintwoorthreevoltsofthesupplyrails 5Thedesignerhasforgottenthatthemaximumoutputvoltageswingisseverelylimitedbyfrequency andthatthemaximumlow frequencyoutputswingbecomeslimitedatabout10kHz 它只能产生几伏的电压输出范围 然而数据却清楚地显示输出应能驱动达到电源电压范围以内2到3伏 11 12 2 Ofcourse theinformationisinfactonthedatasheet butitsrelevancehasnotbeenappreciated Thissortofproblemoccursregularlyfortheinexperienceddesigner Sothemoralisclear alwaystakethenecessarytimetowritedownthefulloperatingrequirementsbeforeattemptingadesign Attentiontothedetailoftheperformancespecificationwillalwaysbebeneficial Itissuggestedthefollowinglistofperformancedetailsbeconsidered 注意句型 Itissuggested thelist beconsidered 12 13 2 Closedloopgainaccuracy stabilitywithtemperature timeandsupplyvoltagePowersupplyrequirements sourceandloadimpedances powerdissipationInputerrorvoltagesandbiascurrents Inputandoutputresistance driftwithtimeandtemperatureFrequencyresponse phaseshift outputswing transientresponse slewrate frequencystability capacitiveloaddriving overloadrecovery 13 14 3 Linearity distortionandnoiseInput outputorsupplyprotectionrequired Inputvoltagerange common moderejectionExternaloffsettrimmingrequirementNotallofthesetermswillberelevant butitisusefultorememberthatitisbettertoconsidertheminitiallyratherthantobeforcedintoretrospectivemodifications 而不要被迫返工 14 15 4Allparametersaresubjecttowidevariations Neverforgetthisfact Howmanytimeshasacircuitbeendesignedusingtypicalvalues onlytofindthatthecircuitdoesnotworkbecausethedeviceusedisnottypical 6Theabovestatementthusposesatrickyquestion whenshouldtypicalvaluesandwhenshouldworst casevaluesbeusedinthedesign 有多少次是在用典型值设计好电路后发现 该电路 只是因为使用的器件不典型而不能工作 在设计中何时应该使用典型值 何时应该使用最不利值 15 16 4 Thisiswherethejudgmentoftheexperienceddesignermustbebroughttobear Clearly ifcertainperformancerequirementsaremandatory thenworst casevaluesmustbeused Inmanycases however thedesirabilityofacertaindefinedperformancewillbeacompromisebetweeneaseofimplementation degreeofimportance andeconomicconsiderations 7 某一规定的性能是否可取要在易实现性 重要性 经济性之间取得折中 16 17 5Donotover specifyorover design Intheend weareallcontrolledbycost anditisreallypointlesstakingasledgehammertocrackanut Simplicityisoftheessencesincethelowpartscountimplementationisinvariablycheaperandmorereliable 8 杀鸡用牛刀 用较少元器件实现 的电路 总是更便宜也更可靠 lowpartscountimplementation 用零件少的实现方案 lowcount 低的计数 数量少 parts 零件 17 18 6 Asanexampleofthisjudgmentaboutworst casedesign consideralow gainDCtransduceramplifierrequiredtoamplify10mVfromavoltagesourcetoproduceanoutputoflVwithanaccuracyof 1 overatemperaturerangeof0 70 C 9Noticethatthespecificationcallsforanaccuracyof 1 Thisimpliesthattheoutputshouldbe1V 10mVfrom0 70 C 一个低增益直流传感器放大器 要求将电压源输出的10mV信号放大 产生1V的输出 在0 70 C范围内达到 1 的精度 18 19 6 Thefirststepis ofcourse toconsiderourlistabove anddecidewhichofthemanyparametersarerelevant Twoofthemostimportanttothis verylimited specificationareoffsetvoltagedriftandgainstabilitywithtemperature Wewillassumethatallinitialerrorsarenegligible rarelythecaseinpractice 对这样 非常有限 的参数 两项最重要的指标是电压偏移和对于温度的增益稳定性 假设所有的初始误差可以忽略不计 19 20 6 Theexperienceddesignerwouldknowthatmostopampshaveaverylargeopen loopgain usuallyverymuchgreaterthan10000 Aclosed loopgainchangeof 1 impliesthattheloopgain asexplainedlater shouldchangebylessthan 100 foraclosed loopgainof100 10 闭环增益 1 的变化意味着环路增益 将在下面说明 的变化在闭环增益为100时应该小于 100 20 21 6 Thisisclearlysoeasilyfulfilledthatthedesignerknowsimmediatelythathecanusetypicalopen loopgainvaluesinhiscalculations However offsetvoltagedriftisanothermatter Manyopampspecificationsincludeonlytypicalvaluesforoffsetvoltagedrift thismaywellbeintheorderof5mV C withanunquotedmaximumforanydeviceof30mV C 11 许多运放技术指标仅仅给出补偿电压偏移的典型值 这很可能会在5mV C的数量级 而未给出任何器件可以达到的最大值30mV C 21 22 6 Ifbychanceweuseadevicewhichhasthisworst casedrift thentheamplifiererrorcouldbe30 70 2100mV 2 1mVovertemperature whichisasignificantproportionofourtotalallowableerrorfromallsources 放大器随温度而产生的误差可为2 1mV 占所有误差源所产生的总的允许误差的相当大一部分 22 23 7 Hereisacase then whereonecanbeconfidentthatthetypicalvalueofopen loopgaincanbeused butwherethemaximumvalueofdriftmaywellcausesignificanterrors Thissortofjudgmentisessentialincarefuldesign andgreatcareisrequiredininterpretingmanufacturers data Thisconsiderationmustbeextendedtoallthedetailslistedaboveapartfromthefactthatworst casevaluesareoftennotquoted 这就是我们可以肯定可使用开环增益典型值的情况 不过最大漂移很可能导致相当大的误差 最不利值通常是不会注明的 23 24 7 Itisoftenfoundthatvaluesgivenarenot100 tested Statisticaltestingisemployedwhich forexample guaranteesthat90 ofalldevicesfallwithintherangespecified Itcouldbeveryinconvenientfortheuserwhoreliesonthespecifiedperformanceandthenfindsthathehasseveralofthe other 10 actuallypluggedintohiscircuit 12 对于某些用户可能很不方便 他们依赖于技术指标所给出的性能 而随后发现却有 另外 10 的器件被用在了他们的电路中 24 PartII DataRegistersandCounters 25 26 NewWords 26 27 NewWords 27 28 1Dataregister Thesimplesttypeofregisterisadataregister whichisusedforthetemporarystorageofa word ofdata Initssimplestform itconsistsofasetofNDflip flops allsharingacommonclock AllofthedigitsintheNbitdatawordareconnectedtothedataregisterbyanN line databus 由共用一个时钟的一组N个D触发器组成 28 29 1 Figure1 1showsa4bitdataregister implementedwithfourDflip flops Thedataregisterissaidtobeasynchronousdevice becausealltheflip flopschangestateatthesametime 29 30 2Shiftregisters Anothercommonformofregisterusedincomputersandinmanyothertypesoflogiccircuitsisashiftregister Itissimplyasetofflip flops usuallyDlatchesorRSflip flops connectedtogethersothattheoutputofonebecomestheinputofthenext andsooninseries 1 它就是一组触发器 通常是D锁存器或RS触发器 联在一起 使其中一个触发器的输出成为下一个的输入 依此形成一串 30 31 2 Itiscalledashiftregisterbecausethedataisshiftedthroughtheregisterbyonebitpositiononeachclockpulse 2Figure1 2showsa4bitshiftregister implementedwithDflip flops 它称为移位寄存器 因为数据在每一个时钟脉冲的作用下通过寄存器移动一位 31 32 3 Ontheleadingedgeofthefirstclockpulse thesignalontheDATAinputislatchedinthefirstflip flop Ontheleadingedgeofthenextclockpulse thecontentsofthefirstflip flopisstoredinthesecondflip flop andthesignalwhichispresentattheDATAinputisstoredinthefirstflip flop etc 3Becausethedataisenteredonebitatatime thiscalledaserial inshiftregister 在下一个时钟脉冲的前沿 第一个触发器的内容被存放到第二个触发器中 而在数据输入端的信号则存放在第一个触发器中 依此类推 32 33 3 Sincethereisonlyoneoutput anddataleavestheshiftregisteronebitatatime thenitisalsoaserialoutshiftregister Shiftregistersarenamedbytheirmethodofinputandoutput eitherserialorparallel Parallelinputcanbeprovidedthroughtheuseofthepresetandclearinputstotheflip flop 每次从移位寄存器输出1比特数据 通过预置和清除触发器输入端可以提供并行输入 33 34 3 Theparallelloadingoftheflip flopcanbesynchronous i e occurswiththeclockpulse orasynchronous independentoftheclockpulse dependingonthedesignoftheshiftregister 4Paralleloutputcanbeobtainedfromtheoutputsofeachflip flopasshowninFigure1 3 触发器的并行加载可以是同步的 或者异步的 取决于移位寄存器的设计 34 35 4 Communicationbetweenacomputerandaperipheraldeviceisusuallydoneserially whilecomputationinthecomputeritselfisusuallyperformedwithparallellogiccircuitry Ashiftregistercanbeusedtoconvertinformationfromserialformtoparallelform andviceversa Manydifferentkindsofshiftregistersareavailable dependinguponthedegreeofsophisticationrequired 计算机与外设之间的通信一般都是串行的 而计算机内部的计算通常都是用并行逻辑电路来执行的 35 36 5Counters weightedcodingofbinarynumbers Inasense ashiftregistercanbeconsideredacounterbasedontheunarynumbersystem Unfortunately aunarycounterwouldrequireaflip flopforeachnumberinthecountingrange Abinaryweightedcounter however requiresonlyflip flopstocounttoN AsimplebinaryweightedcountercanbemadeusingTflip flops 移位寄存器可以看作是一种基于一元数字系统的计数器 一个二进制计数器只需要一个触发器就可以进行N位数据计算 36 37 5 Theflip flopsareattachedtoeachotherinawaysothattheoutputofoneactsastheclockforthenext andsoon Inthiscase thepositionoftheflip flopinthechaindeterminesitsweight i e forabinarycounter the poweroftwo itcorrespondsto 5 这样 触发器在链中的位置决定了它的权重 即对于二进制计数器而言就是它所对应的2的幂 37 38 5 A3 bit modulo8 binarycountercouldbeconfiguredwithTflip flopsasshowninFigure1 4 AtimingdiagramcorrespondingtothiscircuitisshowninFigure1 5 38 39 6 NotethatasetoflightsattachedtoO0 O1 O2woulddisplaythenumbersoffullclockpulseswhichhadbeencompleted inbinary modulo8 fromthefirstpulse 6AsmanyTflip flopsasrequiredcouldbecombinedtomakeacounterwithalargenumberofdigits 注意 一组接在O0 O1 O2上的灯泡将以二进制 模8 形式显示第一个脉冲以来已完成的完整时钟脉冲数 39 40 7 Notethatinthiscounter eachflip flopschangesstateonthefallingedgeofthepulsefromthepreviousflip flop Thereforetherewillbeaslighttimedelay duetothepropagationdelayoftheflip flopsbetweenthetimeoneflip flopchangesstateandthetimethenextonechangesstate i e thechangeofstateripplesthroughthecounter andthesecountersarethereforecalledripplecounters 7 因此将略有时延 这是由一个触发器改变状态到下一个触发器改变状态之间的传播延迟造成的 即状态变化像波纹一样传过计数器 因而这些计数器被称为波纹计数器 40 41 8 Asinthecaseofaripplecarryadder thepropagationdelaycanbecomesignificantforlargecounters Itispossibletomake orbuyinasinglechip counterswhichwillcountup countdown andwhichcanbepresettoanydesirednumber CounterscanalsobeconstructedwhichcountinBCDandbase12oranyothernumberbase 可以通过制作或购买单片芯片计数器来实现计数器的递增计数 递减计数或者预置任何你想要的数字 一个计数器也可以构造出二 十进制 十二进制或者任何进制数的计数器 41 42 9 Acountdowncountercanbemadebyconnectingtheoutputtotheclockinputinthepreviouscounter Bytheuseofpresetandclearinputs andbygatingtheoutputofeachTflipflopwithanotherlogiclevelusingANDgates saylogic0forcountingdown logic1forcountingup thenapresetableup downbinarycountercanbeconstructed 8Figure1 6showsanup downcounter withoutpresetorclear 利用预置和清零端 通过用与门将每一个T触发器的输出与另一个逻辑电平作逻辑运算 则可构成可预置的可逆二进制计数器 42 43 10Synchronouscounters Thecountersshownpreviouslyhavebeen asynchronouscounters socalledbecausetheflip flopsdonotallchangestateatthesametime butchangeasaresultofapreviousoutput Theoutputofoneflip flopistheinputtothenext thestatechangesconsequently ripplethrough theflip flops requiringatimeproportionaltothelengthofthecounter 9 因为他们的状态随前一级的状态变化而变化 而非同时变化 一个触发器输出是下一个的输入 因而状态变化以波动形式通过各触发器 所需时间与计数器长度成正比 43 44 10 Itispossibletodesignsynchronouscounters usingJKflip flops whereallflip flopschangestateatthesametime i e theclockpulseispresentedtoeachJKflip flopatthesametime Thiscanbeeasilydonebynotingthat forabinarycounter anygivendigitchangesitsvalue from1to0orfrom0to1 wheneverallthepreviousdigitshaveavalueof1 10 这很容易做到 对于二进制计数器 只要所有前面的数字都是1 任何给定的数字都会改变它的值 从1变为0 或者从0变为1 44 45 10 Figure1 7showsanexampleofa4 bitbinarysynchronouscounter AcountdowntimercanbemadebyconnectingtheoutputtotheJandK throughtheANDgates Presetandclearcouldalsobeprovided andthecountercouldbemade programmable asinthepreviouscase 45 46 11 Thetimingdiagramissimilartothatshownfortheasynchronous ripple counters exceptthattherippletimeisnowzero allcountersclockatthesametime Itiscommonforsynchronouscounterstotriggeronthepositiveedgeoftheclock ratherthanthetrailingedge 对于同步计数器而言 在时钟上升沿触发比在下降沿触发更为常见 46 PartIII NatureofPhaseLock 47 48 NewWords 48 49 NewWords 49 50 1 Aphaselockloopcontainsthreecomponents Figure1 8 1 Aphasedetector PD 2 Aloopfilter 3 Avoltage controlledoscillator VCO whosefrequencyiscontrolledbyanexternalvoltage 50 51 2 ThephasedetectorcomparesthephaseofaperiodicinputsignalagainstthephaseoftheVCO OutputofPDisameasureofthephasedifferencebetweenitstwoinputs ThedifferencevoltageisthenfilteredbytheloopfilterandappliedtotheVCO ControlvoltageontheVCOchangesthefrequencyinadirectionthatreducesthephasedifferencebetweentheinputsignalandthelocaloscillator 1 压控振荡器的控制电压使频率朝着减小输入信号与本振之间相位差的方向改变 51 52 3 Whentheloopislocked thecontrolvoltageissuchthatthefrequencyoftheVCOisexactlyequaltotheaveragefrequencyoftheinputsignal Foreachcycleofinputthereisone andonlyone cycleofoscillatoroutput 当锁相环处于锁定状态时 控制电压使压控振荡器的频率正好等于输入信号频率的平均值 52 53 3 Oneobviousapplicationofphaselockisinautomaticfrequencycontrol AFC Perfectfrequencycontrolcanbeachievedbythismethod whereasconventionalAFCtechniquesnecessarilyentailsomefrequencyerror 传统的自动频率控制技术不可避免地存在某些频率误差 53 54 4 Tomaintainthecontrolvoltageneededforlockitisgenerallynecessarytohaveanonzerooutputfromthephasedetector Consequently theloopoperateswithsomephaseerrorpresent Asapracticalmatter however thiserrortendstobesmallinawell designedloop 54 55 5 Aslightlydifferentexplanationmayprovideabetterunderstandingofloopoperation Letussupposethattheincomingsignalcarriesinformationinitsphaseorfrequency thissignalisinevitablycorruptedbyadditivenoise Thetaskofaphaselockreceiveristoreproducetheoriginalsignalwhileremovingasmuchofthenoiseaspossible 3 锁相接收机的作用是重建原信号而尽可能地去除噪声 55 56 6 Toreproducethesignalthereceivermakesuseofalocaloscillatorwhosefrequencyisveryclosetothatexpectedinthesignal Localoscillatorandincomingsignalwaveformsarecomparedwithoneanotherbyaphasedetectorwhoseerroroutputindicatesinstantaneousphasedifference Tosuppressnoisetheerrorisaveragedoversomelengthoftime andtheaverageisusedtoestablishfrequencyoftheoscillator 与预计信号频率非常接近的本机振荡器 误差在一定的时间间隔内被平均 56 57 7 Iftheoriginalsignaliswellbehaved stableinfrequency thelocaloscillatorwillneedverylittleinformationtobeabletotrack andthatinformationcanbeobtainedbyaveragingforalongperiodoftime therebyeliminatingnoisethatcouldbeverylarge 4Theinputtotheloopisanoisysignal whereastheoutputoftheVCOisacleaned upversionoftheinput Itisreasonable therefore toconsidertheloopasakindoffilterthatpassessignalsandrejectsnoise 该信息可通过长时间的平均得到 从而消除可能很强的噪声 57 58 8 Twoimportantcharacteristicsofthefilterarethatthebandwidthcanbeverysmallandthatthefilterautomaticallytracksthesignalfrequency Thesefeatures automatictrackingandnarrowbandwidth accountforthemajorusesofphaselockreceivers Narrowbandwidthiscapableofrejectinglargeamountsofnoise itisnotatallunusualforaPLLtorecoverasignaldeeplyembeddedinnoise 窄带能够抑制大量的噪声 难怪锁相环常用来恢复深深地淹没在噪声中的信号 58 59 9Historyandapplication AnearlydescriptionofphaselockwaspublishedbydeBellescizein1932andtreatedthesynchronousreceptionofradiosignals Superheterodynereceivershadcomeintouseduringthe1920s buttherewasacontinualsearchforasimplertechnique oneapproachinvestigatedwasthesynchronous orhomodyne receiver Inessence thisreceiverconsistsofnothingbutalocaloscillator amixer andanaudioamplifier 但人们一直努力寻求更简单的接收技术 59 60 9 Tooperate theoscillatormustbeadjustedtoexactlythesamefrequencyasthecarrieroftheincomingsignal whichisthenconvertedtoanintermediatefrequencyofexactly0Hz Outputofthemixercontainsdemodulatedinformationthatiscarriedassidebandsbythesignal Interferencewillnotbesynchronouswiththelocaloscillator andthereforemixeroutputcausedbyaninterferingsignalisabeat notethatcanbesuppressedbyaudiofiltering 5 它随后被转换成严格为0Hz的中频 干扰与本振不同步 因此干扰引起的混频输出是一个拍音 可用音频滤波器抑制 60 61 10 Correcttuningofthelocaloscillatorisessentialtosynchronousreception anyfrequencyerrorwhatsoeverwillhopelesslygarbletheinformation Furthermore phaseofthelocaloscillatormustagree withinafairlysmallfractionofacycle withthereceivedcarrierphase Inotherwords thelocaloscillatormustbephaselockedtotheincomingsignal 任何一点频率误差都将严重损坏信号 此外本振的相位必须与接收的载波相位一致 其间的误差限于周期的很小一部分 61 62 11 Forvariousreasonsthesimplesynchronousreceiverhasneverbeenusedextensively Present dayphaselockreceiversalmostinvariablyusethesuperheterodyneprincipleandtendtobehighlycomplex Oneoftheirmostimportantapplicationsisinthereceptionoftheveryweaksignalsfromdistantspacecraft 62 63 11 Thefirstwidespreaduseofphaselockwasinthesynchronizationofhorizontalandverticalscanintelevisionreceivers Thestartofeachlineandthestartofeachinterlacedhalf frameofatelevisionpicturearesignaledbyapulsetransmittedwiththevideoinformation 与视频信号一起传送的脉冲发出电视图像每一行的开始信号和隔行扫描的半帧开始信号 63 64 12 AsaverycrudeapproachtoreconstructingascanrasterontheTVtube thesepulsescanbestrippedoffandindividuallyutilizedtotriggerapairofsinglesweepgenerators Aslightlymoresophisticatedapproachusesapairoffree runningrelaxationoscillatorstodrivethesweepgenerators Inthiswaysweepispresentevenifsynchronizationisabsent 作为一种非常粗糙的重建电视显象管扫描光栅的方法 这些脉冲可以剥离出来单独用于触发一对扫描发生器 64 65 13 Free runningfrequenciesoftheoscillatorsaresetslightlybelowthehorizontalandverticalpulserates andthestrippedpulsesareusedtotriggertheoscillatorsprematurelyandthustosynchronizethemtothelineandhalf framerates half framebecauseUnitedStatestelevis