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1 1Part 4 Computer Control Theory4.1 Microcomputer4.2 Sample-and-Hold Amplifier4.3 Microcontroller4.4 Embedded System4.5 Temperature Control Experiment2 24.1.1语言现象论文的标题科技论文的标题和摘要是信息及成果交流的重要途径，是进行论文检索的有效工具。科技论文的标题是概括全文和吸引读者的重要部分，标题质量的好坏直接影响着论文的“取舍”、受众范围的大小和信息传递的畅通与否。因此有必要熟知它们的特征，写出客观明晰、表述准确、语言精练、符合规范、且能引起读者兴趣的标题。4.1 Microcomputer3 31标题的长度标题在整个文章构成中起到画龙点睛的作用，应力求重点突出，言简意赅。标题一般在10个单词左右，不超过16个单词。如果太长可采取增加副标题或标点符号的办法。如：LowFrequencyWidebandSAM低频带超显微镜RiskControlamidRapidExpansion快速增长中的风险控制HowtoRecognizeandTranslatetheIntentionoftheSourceText4 4ACulturalConsiderationinTranslation源语意识的识别与翻译关于翻译的文化因素思考Substitution:TheThirdFunctionofEnglishPunctuationMarks英语标点符号的第3种功能：替代功能5 52标题的书写特征标题的第一个词(不管实词或虚词)和每一个实词(形容词、副词、名词、动名词)的第一个字母都大写，虚词(介词、连词、冠词等)要小写；也可以所有字母全大写；还可以标题的第一个词的首字母大写，其余单词均小写。如：REVIEWANDPROSPECTOFCOMPUTERCONTROLSYSTEMINCHINA中国计算机控制技术发展的回顾和展望ReviewandProspectofComputerControlSysteminChina中国计算机控制技术发展的回顾和展望6 6Ondesignandrealizationofthedatabaseinthelocomotivecircuitdetector机车线路检测仪的数据库设计与实现7 73标题的内容特征标题中应包含所给出的关键词，能准确反映论文的性质和主要内容，有的还涉及到研究的手段或方法。另外标题的下方应加上作者和作者的单位。ResearchonControllabilityofMagneticSuspensionwithHighTemperatureSuperconductingElectromagnet(标题中的controllability，magneticsuspension，hightemperaturesuperconductingelectromagnet为文中的关键词)高温超导磁悬浮系统可控性研究8 84标题的常用句式英语的标题多用动名词、名词短语、介词短语，带疑问词的动词不定式或几种形式混合。汉语经常使用一些词，像“基于”，“的设计”，“的研究”，“的方法”，“的应用”，“的思考”等，如：DesignofaSimpleWirelessPoweringSystem简易无线电供电系统的设计AnImprovedAllDigitalPhase-lockedLoopDesign一种改进的全数字锁相环设计ChaoticSignalDenoisingBasedonThresholdSelectionofWaveletTransform9 9基于小波变换阈值决策的混沌信号去噪研究OntheMisconceptionsinTranslationStudiesandTheoriesinOurCountry国内翻译界在翻译研究和翻译理论认识上的误区10105标题的修饰语标题经常带有前置或后置修饰语，有时前后可同时带有修饰语。可作修饰语的词有冠词、代词、形容词、名词、分词、介词短语等，冠词和不定冠词经常省略，但应注意省略冠词、介词以不影响概念、意义的准确性为原则。如：DistributedandCooperativeControlforUrbanRoadNetworkTraffic城市路网交通分散协调控制ABothMatchedDynamicSchedulingAlgorithm一种双匹配动态调度算法11116标题的缩略形式标题可出现专有名词或专有名词的缩略形式。如：TheStudyHeadwayofDTC-PMSM永磁同步电机直接转矩控制的研究进展MotorolaMotorControllerDSP56F807Motorola电机控制器DSP56F80712127标题的专业术语词熟悉了科技论文的标题的特点后，对标题就需要认真研读，准确理解每一个词表达的含义，特别是遇到专业词汇时，更应仔细查找资料或咨询专业人士，选择规范通用的表达法。在准确理解的基础上，找准中心词，理顺主次逻辑关系，根据语法结构恰当地进行表达。13134.1.2SpecifiedEnglishWordsfabricatevt.制造；伪造；装配cartridgen.弹药筒，打印机的(墨盒)；暗盒；笔芯；一卷软片entryn.入口；进入；登记；条目；对土地的侵占；商报关手续trackballn.追踪球；轨迹球joystickn.操纵杆，控制杆bitpadn.写字板multiplexern.多工器；多路器；多路转接器1414editorn.编者，编辑；社论撰写人；编辑装置compilern.编辑者，汇编者；编译器；编译程序ampleadj.丰富的；足够的；宽敞的crucialadj.决定性的；重要的；定局的；决断的benchn.长凳；工作台desktopn.桌面；台式机peripheraladj.外围的；次要的retrievevt.重新得到；恢复；检索vi.找回猎物n.检索；恢复，取回1515camcordern.摄录像机；便携式摄像机pointingdevice定点设备beshippedwith与一起推出back-upn.备份adj.作支援的vt.为做备份intermixvt.使混杂；使混合vi.混杂；混和built-inadj.嵌入的；固定的n.内置16164.1.3TextMicrocomputerInthepastfewyears,enormousadvanceshavebeenmadeinthecost,power,andeaseofuseofmicrocomputersandassociatedanaloganddigitalcircuits.Itisnowpossible,witharelativelysmallexpenditure,topurchaseamicrocomputersystemthatwilltakedata,quicklyanalyzethem,anddisplaytheresultsorcontrolaprocess.Thishasbeenmadepossiblebythedevelopmentoftechnologythatcanfabricatemillionsoftransistors,diodes,resistors,capacitors,andconductorsonasinglesiliconintegratedcircuitchip.1717Normally,themicrocomputerisequippedwithanumberofstandarditems:themicroprocessorchipandassociatedcircuits,random-accessmemorychips,removablefloppyandcartridgediskdrives,magneticharddiskdrives,opticaldiskdrives,key-boards,videodisplayscreens,serialinterfaces,printers,andx-yentrydevicessuchasthemouse,trackball,joystick,bitpad,andtouch-sensitivedisplayscreen.1818However,dataacquisitionandcontrolrequireadditionalcomponents,suchasdigitalandanaloginput/output(I/O)ports,andcounter/timers.Analoginputportscontainanalogmultiplexers,sample-and-hold(S/H)amplifiers,andanalogtodigital(A/D)converters.Analogoutputportscontaindigital-to-analog(D/A)converters.1919Evenfordesignsrequiringonlyamicroprocessorandafewadditionalcircuits,thereareconsiderableadvantagestousingtheresourcesofthemicrocomputerduringthedevelopmentstage.Theseincludeprogramcodeeditorsandcompilers,anoperatingsystemforthestorageandmanipulationofcodeanddatafiles,andamplerandom-accessmemory.Inselectingasystemfordataacquisitionandcontrol,themicrocomputeritselfisacrucialcomponent(Fig.4.1).2020Themicrocomputerissufficientlysmalltofitonalaboratorybench(ordesktop)andyetcontainsthefollowingcomponents:The microprocessor isanintegratedcircuitthatreadsprograminstructionsfrommemoryandusesthemtodeterminethesequenceofactionsthatitperforms.Itisconnectedtomemoryandperipheralcircuitsbyanaddressbus,adatabus,andcontrollines.2121Theseactionsincludereadingdataandinstructionsfrommemory,performingcalculations,executingdifferentinstructionsdependingontheoutcomeofacalculation,printingdata,andtransferringdatatoandfromperipheraldevicessuchasharddisks.Microprocessorsvarygreatlyintheirspeedanddata-handlingcapability.Random-access memory(RAM)usuallyconsistsofhigh-speedsemiconductormemorychipsthatareusedtostoreandretrieveprograminstructionsanddata.2222Thehighestdata-acquisitionspeedsareachievedwhenexternaldataarereaddirectlyintoRAM,sothesizeoftheRAMplacesalimitonthenumberofdatavaluesthatcanbesampledrapidly.Common user interface devicesarethekeyboard,videodisplayscreen,printer,mouse,joystick,andtrackball.Somesystemsprovidevoiceinputandsynthesizedspeechoutput.TheIEEE-1284interfacestandardincludesthestandardparallelprinter(SPP)portaswellasotherenhancements.Theuniversalserialbus(USB)isthecurrentstandardforkeyboardsandpointingdevices.2323Forhigherspeedtransfers(externalharddevices,digitalcamcorders,HDTV),theIEEE-1394standardhasrecentlybeenintroduced.2424Fig.4.1crucialcomponentinamicrocomputer2525Magnetic disk memoryisusedforthelong-termstorageofprogramsanddata,andconsistsofoneormoreflatcircularplatescoatedwithamagneticsurface.Magneticdiskcapacitiesrangefrom500kbytesto2Mbytesforsmallremovablefloppydisksandfrom1to20Gbytesormoreforharddisks,Accesstimeconsistsofafixeddelayoftensofmilliseconds(fortheread/writeheadtolocatethedesiredtrack)andatransfertimeoftypically1sper16-bitword.2626Optical disk memoryincludestheCD-ROMandtheDVD-ROMdisks.TheCD-ROM(compactdisk-read-onlymemory)andtheDVD-ROM(digitalversatiledisk)drivesuseopticalstorageandretrievaltechnologythatwasdevelopedforthemusicandentertainmentindustry.ThecapacityoftheCD-ROMisover600MbytesandabouttentimeslargerfortheDVD-ROM.Bothare12cmindiameter.MicrocomputersandworkstationsarecommonlyshippedwithaCD-ROMcontainingaback-upcopyofthesystemsoftwareandon-linedocumentation,2727eliminatingmanyfloppydisksandthousandsofpagesofpaper.CD-W(writeonce)andCD-RW(rewritable)andDVD-RAM(random-access)technologyallowsinformationtobewrittenontothesedisks.Operating systems havedevelopedoverthepastthirtyyearsfortwomainpurposes.First,theyprovideaconvenientenvironmentforthedevelopmentandexecutionofprograms.Second,2828operatingsystemsattempttoschedulecomputationalactivitiestoensuregoodperformanceofthecomputingsystem.Theoperatingsystempermitstheusertomanipulateprogramanddatafilesandsupportsahigh-levelcompiledprogramming1anguage(FORTRAN,Pascal,C,compiledBASIC,etc.).A compilersfunctionistotranslateahigh-levellanguageintomicroprocessorcodethatisableto:(1)Performnumericalcomputationsandconditionalbranching;2929(2)Communicatedirectlywithadata-acquisitionandcontrolboardorparallelI/Oport(seebelow);(3)Readandwritefilestothedisk.Additionalusefulfeaturesinclude：(1)Afullrangeofscientificfunctions(sine,cosine,exp,log,etc.),andtheabilitytocomputeusingfloating-pointrepresentation,whichcanhandleverysmallandverylargenumbers(forexample,80-bitextendedprecisioncanhandlenumbersfrom10-4.932to10+4.932withaprecisionof19decimaldigits);3030(2)Theabilitytowritefunctionsinassemblycodeforgreaterspeedduringdataacquisition(somecompilerspermitintermixedassemblycodeandhigher-levelcode);(3)Abuilt-ineditorthatdisplayslinescausingcompilationerrorsandpermitsimmediatecorrection;(4)Asinglecommandthatcompilesallchangedprogrammodules,linksallnecessarymodules,andrunstheresult.An analog input/output port(alsocalledadata-acquisitionandcontrolcircuit),withtherequiredspeedandnumberofA/DandD/Aconversioncircuits.3131A parallel input/output portwithsufficientspeed,iftheanaloginput/outputportisnotavailable.Inthiscase,itbecomesnecessarytodesignandbuildadata-acquisitioncircuitforconnectiontotheparallelI/Oport.A counter/timer thatcandetermineelapsedtimestoanaccuracyoftypically1s,countinputpulses,orproduceoutputpulsesofanydesiredwidthandperiodwithanaccuracyoftypically1s.3232Themicroprocessorcommunicateswiththeothercomponentsofthemicrocomputerbyanaddressbus,adatabus,andanumberofcontrollines(Fig.4.1).Theaddressbusallowsthemicroprocessortoselectparticularcomponentsindividually.EachcomponenthasauniqueassignedaddresswhetheritisaRAMlocation,anI/Oportregisterorotherperipheralcircuit.Anaddressdecoderproducesaselectpulsewhenevertheassignedaddressappearsontheaddressbus.Forexample,a16-MbitRAMchiphasaninternaladdressdecoderwith24inputlinesandl6millionselectlines,oneforeachmemorybitthatcanbeselected.3333Thedatabusisusedtotransmitdatawordstoandfromthemicroprocessoranditsassociatedcircuits.Insomesystems,memorylocationsandexternaldevicesaredistinguishedfromeachotherbyaspecialcontrolbit.Inothers,alargeblockofmemoryaddressspaceisreservedforexternaldevices.Sincemanydevicesareattachedtothedataandaddressbusesandatanyinstantonlyonecanbesendingdata,controllinesareusedtoindicatewhenthebusisbusy,3434whenasendingdevicerequestsuseofthebus,whenuseisgranted,etc.Thesedetailsarementionedtooutlinetheorganizationofthemicrocomputer.3535 Notes1Itisnowpossible,witharelativelysmallexpenditure,topurchaseamicrocomputersystemthatwilltakedata,quicklyanalyzethem,anddisplaytheresultsorcontrolaprocess.现在花相对较少的钱就可以买到一台微型计算机，不仅可以进行数据采集、分析、显示结果，而且也可以进行过程控制。2Theoperatingsystempermitstheusertomanipulateprogramanddatafilesandsupportsahigh-levelcompiledprogramming1anguage.3636操作系统允许用户对程序和数据文件进行操作，并且支持高级编程语言。37374.1.4ReadingMaterialsNetworked Control SystemANetworkedControlSystem(NCS)isacontrolsystemwhereinthecontrolloopsareclosedthroughareal-timenetwork.ThedefiningfeatureofanNCSisthatcontrolandfeedbacksignalsareexchangedamongthesystemscomponentsintheformofinformationpackagesthroughanetwork.ThefunctionalityofatypicalNCSisestablishedbytheuseoffourbasicelements:(1)Sensors,toacquireinformation,(2)Controllers,3838toprovidedecisionandcommands,(3)Actuators,toperformthecontrolcommandsand,(4)Communicationnetwork,toenableexchangeofinformation.ThemostimportantfeatureofaNCSisthatitconnectscyberspacetophysicalspacethus,enablingexecutionofseveraltasksfromlongdistance.Inaddition,networkedcontrolsystemseliminateunnecessarywiringthus,reducingthecomplexityandtheoverallcostindesigningandimplementingthecontrolsystems.3939Theycanalsobeeasilymodifiedorupgradedbyaddingsensors,actuatorsandcontrollerstothemwithrelativelylowcostandnomajorchangesintheirstructure.Moreover,featuringefficientsharingofdatabetweentheircontrollers,NCSareabletoeasilyfuseglobalinformationtomakeintelligentdecisionsoverlargephysicalspaces.Theirpotentialapplicationsarenumerousandcoverawiderangeofindustriessuchasspaceandterrestrialexploration,accessinhazardousenvironments,factoryautomation,4040remotediagnosticsandtroubleshooting,experimentalfacilities,domesticrobots,aircraft,automobiles,manufacturingplantmonitoring,nursinghomesandtele-operations.AdventanddevelopmentoftheinternetcombinedwiththeadvantagesprovidedbyNCSattractedtheinterestofresearchersaroundtheglobe.Alongwiththeadvantages,severalchallengesalsoemergedgivingrisetomanyimportantresearchtopics.Newcontrolstrategies,kinematicsoftheactuatorsinthesystems,4141reliabilityandsecurityofcommunications,bandwidthallocation,developmentofdatacommunicationprotocols,correspondingfaultdetectionandfaulttolerantcontrolstrategies,real-timeinformationcollectionandefficientprocessingofsensorsdataaresomeoftherelativetopicsstudiedindepth.TheinsertionofthecommunicationnetworkinthefeedbackcontrolloopmakestheanalysisanddesignofanNCScomplex,4242sinceitimposesadditionaltimedelaysincontrolloopsorpossibilityofpackagesloss.Dependingontheapplication,time-delayscouldimposeseveredegradationonthesystemperformance.Moreover,amostcriticalandimportantissuesurroundingthedesignofdistributedNCSswiththesuccessivelyincreasingcomplexityistomeettherequirementsonsystemreliabilityanddependability,4343whileguaranteeingahighsystemperformanceoverawideoperatingrange.Thismakesnetworkbasedfaultdetectionanddiagnosistechniques,whichareessentialtomonitorthesystemperformance,receivemoreandmoreattention.44444.1.5Homework1Pleasesumupthemainpointsofthetextinseveralsentences.2TranslatethefollowingsentencesintoChinese.(1)Withthedevelopmentofbasicautomationandprocesscontroltechniques,asthecoreoflargescalecomputercontrolsystemtheLANwillhavewidefutureinitsapplicationanddevelopment.(2)Thepaperintroducesapatternofcomputercontrolsystemofjetloom,whichhasareferencesignificanceforanalyzingstructureandprincipleofcomputercontrolsysteminotherjetloom.4545(3)Withtherapiddevelopmentofthehydraulictechnologyandcomputercontroltechnology,thehighperformanceandhighqualityhydraulicpumpisactivelydemandedintheengineeringapplication.(4)Withtherapiddevelopmentofpowerelectronictechnologyandcomputercontroltechnology,ithasbecomedevelopmenttrendthatACspeedregulationsystemreplacesDCmotorspeedregulationsystem.4646(5)Thehardwaredesignforcomputercontrolsysteminsyntheticfiberindustryandthenetworkcompositionandfunctionofthecomputercontrolsystemwereintroduced.47474.2.1语言现象摘要和关键词摘要(abstract)是位于论文正文之前的一段概括性文字，篇幅较短，层次清楚，字数一般在200300字之间，便于读者查找信息。摘要具有独立性(可独立于论文全文)、概括性(简要概括论文的主要内容)和完整性，好的摘要能让读者不阅读正文的全文就能获得必要的信息，因此常被科技工作者利用。如：4.2 Sample-and-Hold Amplifier4848Abstract：Generaldesignflow,methodandrelatedsoftwaretoolsareintroducedinthedesignofthecommunicationsystemwithprogrammablelogicdevices.AnexampleisgivenfortheanalysisoftheemulationresultoftheFPGAdesignandtheconclusionisverified.Andtheimportanceoftheemulationverificationinthedesignispointedout.1科技论文摘要的分类及内容特征摘要的写法分为三类。一是指明实质性内容的实验性和技术性较强的论文摘要，称为报道摘要，也称信息型摘要(informativeabstract)。4949二是指明论文主题范围的摘要，称为指示性摘要，也称概括型摘要(indicativeabstract)。前者一般要包括目的(purpose)、方法(method)、结果(数据)(result)和结论(conclusion)四要素。其结构严谨，逻辑严密，层次分明，多为理工科的学术论文摘要。后者把重点放在概述论文的论点、分析过程和结论上。三是信息型与概括型的结合。50502科技论文摘要的语言特征时态和语态。在撰写摘要时根据不同的情况可使用不同的时态和语态。当介绍具有普遍事实的背景资料时，多用一般现在时；当概述具有某种研究动向的背景资料时，多用现在完成时。在描述实验目的时，当以thepaper作主语或出现Inthispaper,we等类似的句式时，常用一般现在时态；当以Theobjectiveof或Inthisstudy,we等类似的句式出现时，多用一般过去时。当描述实验方法时多用一般过去时，但当涉及到一些算法、分析方法等时也用一般现在时。5151现在科技摘要中为了生动、有力、直接，常使用主动语态，为了客观、强调、简洁也多使用被动语态。具体用什么时态应根据行文的需要，不能过于死板。如：Thispaperpresentsanewalgorithmcalledbothmatchedalgorithmwhichissuitabletoindependentjobschedulingonheterogeneousprocessorplatforms.本文提出了适于异构环境独立任务调度的双匹配动态调度算法。Usingdigitalsignalprocessor(DSP),TMS320F240,wedeveloponefrequencyconversionadjustable-speedsystembasedonvectorcontrolprinciple.5252以电机控制专用的DSP芯片TMS320F240为核心，设计开发了一套基于矢量控制的变频调速系统。名词化结构。科技文体摘要要求叙述重点突出，简练客观，信息丰富，逻辑性强，而带有多个修饰语的名词化结构恰好能担此重任，因此科技论文摘要多用名词化结构。如：Thesubstitutionofthenewequipmentfortheoldwouldresultinaconsiderableincreaseinproduction.新设备替代老设备将会使产量大大增加。Thebasicmethodfortheimprovementofsoilistheapplicationoforganicfertilizer.5353改良土壤的基本方法是使用有机肥。长句。科技论文摘要信息集中，逻辑结构分明，因此大量运用状语和其他修饰成分。如：BasedonanalyzingthemultipleUCAVmissionassignmentcharacteristics,anintegerprogrammingbasedmissionassignmentmethodformultiplecooperativeUCAVsisproposed.在深入分析多UCAV任务分配问题的特点的基础上，提出求解多UCAV协同任务分配的整数规划方法。5454用关键词(keywords)对科技期刊论文进行标引，已成为科技期刊编辑出版的一个重要组成部分，成为科技期刊编辑出版标准化、规范化的一项基本要求。科学技术报告、学位论文和学术论文的编写格式(GB7713-87)中指出：“关键词是为了文献标引工作从报告、论文中选取出来用以表示全文主题内容信息款目的单词或术语”。关键词是对揭示和描述论文主题来说是重要的、带关键性的(可以作为检索“入口”的)那些语词。关键词是科技文章中最重要的且出现频率最高的词或词组，一般使用名词，词数为38个。5555关键词应是精心选择的，但很多人在选择关键词时很随意，用词不规范，常选择一些泛意词。在一些学报论文中所标引的关键词有：分析、研究、探讨、应用、讨论、评价、建议、改革、对策、特点、性质、方法、质量、影响、差异、原则、发展、不同、缘由等，这些词过于空泛，又无修饰限定成分，缺乏特指性、专指性，不具有检索意义。这些词适用于不同的领域，可用以解说不同的问题，把它们选作关键词不便于论文数据库的分类管理。如果用这类词到数据库检索论文，一下可检索到成千上万篇，失去检索作用。5656规范的摘要和关键词对论文是十分必要的，绝不是可有可无的。特别是在网络环境下，规范的摘要和关键词更为重要。作者撰写论文需要读者阅读、需要传播。论文如无人阅读就是几页废纸。论文能否被阅读，论文摘要和关键词起到非常重要的作用。现在是信息爆炸时代，文献浩如烟海，往电脑里输一个主题词，会出现几十篇上百篇或上千篇的有关论文，读者不可能把这些文章都读完。要先读摘要，来决定是否阅读论文全文。通过阅读摘要来选择最需要阅读的论文。5757选用恰当的关键词，论文才能被数据库检索，选用了不恰当的关键词，数据库无法检索，读者检索不到你的论文，论文被阅读的可能性就会大大减少。撰写论文时要编写高质量的摘要，标引高质量的关键词。58584.2.2SpecifiedEnglishWordsschematicadj.图解的；概要的n.图解视图；原理图exercisen.练习；运动；运用vt.练习；锻炼；使用；使忙碌vi.运动；练习offsetvoltage偏移电压；补偿电压linearityerror线性误差settlingtime沉淀时间，校正时间；稳定时间；调节时间slewn.回转；沼地；极多vi.扭转；侧滑；转向；猛拐vt.使扭转；使旋转5959droopvi.下垂；萎靡；凋萎vt.使下垂n.消沉；下垂feedthroughn.引线，导线，馈通adj.直通的freezevi.冻结；冷冻；僵硬vt.使冻住；使结冰n.冻结；凝固aperturen.孔，穴；缝隙；光圈，孔径n.引线aperturejitter孔径抖动；缝隙抖动manifestvt.证明，表明；显示vi.显示，出现adj.明白的；显然的，明显的accountfor对负有责任；对做出解释；说明的原因60604.2.3TextSample-and-hold AmplifierThesample-and-holdamplifierhasananaloginput,ananalogoutput,andadigitalcontrolinput.Itconsistsbasicallyofanamplifier,aswitch,andacapacitor(Fig.4.2).InsamplemodeS,Vo=Vi.InholdmodeH,VoisdeterminedbytheholdingcapacitorCH.Thecontrolinputdetermineswhetherthedeviceisoperatinginsamplemodeorholdmode.Inthesamplemode,theswitchisclosedanditoperatesasatypicalamplifieroropamp.6161Intheholdmode,theswitchisopenandtheoutputisideallyconstant,independentoftheinput.Thisconstantvalueistheoutputvaluepresentwhenthemodewaslastswitchedfromsampletohold.6262Fig.4.2unity-gainsample-and-holdamplifier6363SeeFig.4.3foraschematicoftheanaloganddigitaldelaysthatoccurduringthesampletoholdtransition.Fig.4.4isoutputresponseofthesampleandholdamplifiertoanarbitrarywaveformasthelogiccontrolisexercised.Thesample-and-holdamplifierisusedtoprovideasteadyinputduringanalog-to-digitalconversion.Wenowdiscussthepropertiesofthisdeviceinthesamplemode,theholdmode,andwhenmakingthetransitionbetweenmodes.6464Fig.4.3analoganddigitaldelay6565Fig.4.4outputresponseofthesampleandholdamplifier6666Insamplemodeofoperation,thesample-and-holdamplifierhaspropertiessimilartothoseofanyamplifieroropamp:(1)TheoutputoffsetvoltageistheoutputvoltageVoforzeroinputvoltageVi.(2)ThelinearityerroristhedeviationbetweenthevoltagegainanditsaveragevalueoveraspecifiedrangeofVi.(3)Thesettlingtimeisthetimerequiredfortheoutputtoreachitsfinalvalue(withinaspecialaccuracy)afterafull-scaleanaloginputstep.6767(4)ThebandwidthisthehighestfrequencyatwhichGhasdroppedlessthan3dBfromitslow-frequencyaverage.(5)Theslewingrateisthemaximumrateofchangeafterananaloginputsteporafterahold-to-sampletransition.Inholdmode,theoutputshouldremainconstantandindependentoftheinput:(1)Droopisthedriftinoutputvoltageduetochargeleakagefromtheholdcapacitorthroughtheswitch,theamplifier,orthecapacitoritself.IftheleakagecurrentisI,.6868(2)Feedthroughisthefractionofinputsignalthatappearsattheoutput,causedprimarilybythecapacitanceoftheopenswitch.Whensamplingananalogwaveform,thesample-to-holdtransitionisusedtofreezetheinstantaneousvalueoftheinputwaveformattheoutputsothatthevaluecanbeconvertedintoadigitalform.Ideally,whenthesampletoholdedgeisreceived,theoutputshouldholdatitscurrentvaluewithoutdelayoramplitudeshift.6969Thetypesofdeviationbetweenthisidealbehaviorandtheactualbehavioraredescribedbelow(andillustratedinFig.4.3):(1)Thecontroldelaytcdisthetimebetweentheedgeofthesample-to-holdcommandandthetimewhentheswitchbeginstoopen.(2)Theaperturetimetaisthetimerequiredfortheswitchtoopenandcharacterizesonlytheresponsetimeoftheswitch.Thevaluethatisheldattheoutputisdeterminedbytheaverageinputvalueduringtheaperturetime.7070(3)theanalogdelaytadisthedelaybetweentheanaloginputandtheoutputinsamplemode.(4)Theaperturedelaytdisthetimebetweentheedgeofthesample-to-holdcommandandthetimewhentheinputwasequaltotheheldvalue.Becauseoftheanalogdelay,thisquantitycanbenegative:7171(5)Theaperturejittertdisthermsvariationinaperturedelaycausedbynoiseinthecontrolsignalandswitchingcircuit.ItmanifestsitselfasarandomvariationV0intheheldvalueanddependsontheslope：7272(6)Thechargetransfererroristheoffseterrorintheheldvaluecausedbychargedumpedontotheholdingcapacitorfromtheswitchingcircuit.Ideally,thisshouldbeafixedoffset,independentofinputvoltagelevel.ThiserrorcanbereducedbyincreasingthevalueoftheholdingcapacitorcCH.(7)Thesample-to-holdoffsetistheshiftinoutputlevelduringthetransitionfromthesamplemodetotheholdmodeafterthechargetransferhasbeenaccountedfor.Itmaydependonthecharacteristicsoftheinputsignalandisalsocalledtheoffsetnonli
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