chapter8.ppt

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1、Chapter8Discrete(Sampling)System8.1Introduction8.2Z-transform8.3Mathematicaldescribingofthesamplingsystems8.4Time-domainanalysisofthesamplingsystems8.5Therootlocusofthesamplingcontrolsystems8.6Thefrequencyresponseofthesamplingcontrolsystems8.7Thedesignofthe“least-clap”samplingsystem

2、sChapter8Discrete(Sampling)SystemMakeaanalogsignaltobeadiscretesignalshownasinFig.8.1.tx(t)0t1t2t3t4t5t6Fig.8.1signalsamplingx(t)x*(t)x(t)—analogsignal.x*(t)—discretesignal.8.1.2Idealsamplingswitch—samplerSampler—thedevicewhichfulfillthesampling.Anothername—thesamplingswitch—whichwo

3、rkslikeaswitchshownasinFig.8.2.Ttx*(t)0tx(t)0Fig.8.2samplingswitch8.1.3Someterms1.SamplingperiodT—thetimeintervalofthesignalsampling:T=ti+1－ti.8.1Introduction8.1.1Sampling8.1.3Someterms2.Samplingfrequencyωs—ωs=2πfs=2π/T.3.PeriodicSampling—thesamplingperiodTs=constant.4.Variableperio

4、dsampling—thesamplingperiodTs≠constant.5.Synchronoussampling—notonlyonesamplingswitchinasystem,butallworkSynchronously.6.Multi-ratesampling.7.Opportunity(Random)sampling.Wemainlydiscusstheperiodicandsynchronoussamplinginchapter8.8.1.4Sampling(ordiscrete)controlsystemThereareoneormor

5、ediscretesignalsinacontrolsystem—thesampling(ordiscrete)controlsystem.Forexamplethedigitalcomputercontrolsystem:A/DD/Acomputerprocessmeasurer(t)c(t)e(t)－e*(t)u*(t)u(t)Fig.8.3computercontrolsystem8.1.5SamplinganalysisExpressionofthesamplingsignal:8.1IntroductionItcanberegardedasFig.8

6、.4:0tx*(t)tx(t)0TtδT(t)0×＝modulatingpulse(carrier)modulatedwaveModulationsignalFig.8.4samplingprocessx(t)x*(t)8.1.5SamplinganalysisWehave:Thismeans:forthefrequencyspectrumofx(t)showninFig.8.5,thefrequencyspectrumofx*(t)islikeasFig.8.6.Fig.8.5Fig.8.6FilterOnly:couldbereproduced8.1.5S

7、amplinganalysisIftheanalogsignalcouldbewholerestitutedfromthesamplingsignal,thesamplingfrequencymustbesatisfied:8.1.7zero-orderholdUsuallythecontrolledprocessrequiretheanalogsignals,soweneedadiscrete-to-analogconvertershowninFig.8.5.discrete-to-analogconverterx*(t)xh(t)Fig.8.7D/Acon

8、vertSowehave:8.1.6S