67基于LabVIEW的虚拟双踪示波器的设计外文翻译

1外文文献ADAQcardbasedmixedsignalvirtualoscmoscopeAbstractComplexsignalsfindmanyapplicationsinSONAR,RADAR，EchoLocationSystemsandforstudyingtheresonantfrequencies.DigitalStorageOscilloscopcs(DSO)isusedthesedaysforacquisitionanddisplayofroutinesignals.Thisinstrument,foundineverymeasurementlaboratory,thoughpotentindisplayingsimpleperiodicwaveformslikesinusoidsfailswhenfrequency-varyingtimesignalsareapplied,Thisproblemsurfacesbecausetheunderlyingtechniqueofoscilloscopeusedtotriggerthewaveformdoesnotacquiescewithcomplexsignalslikechirp.Readysolutiontothisproblemisthemixedsignaloscilloscope.Thisisacostlysolutionandsmalllaboratoriescannotaffordtohavethecostlyinstruments.Inthispaper,acosteffectiveDAQcardbasedmixedsignalvirtual0scilloscopeisproposedtostudythecomplexsignals.Anintelligenttechnique,WeightedHammingDistance(WHD)algorithmwasusedtoaccuratelytriggerthecomplexwaveforms.Alsoforfrequencydomainanalysis,JointTimeFrequencyAnalysis(JTFA)techniqueswereused.ALabVlEW'TMbasedvirtualinstrumentwasdesignedanddevelopedwithacapabilitytoacquire,displayandanalyzethetriggeredsignal.TheintegratedprogramminglanguageLabVIEWTMwaschosenasitoffersmanysimplereadytousefunctions.Inawaytheproposaloffersacosteffective,fastandflexiblesolutiontotreatthecomplexsignals.Theneedtocreatesuchsolutionsistheconsequenceofcostlyhardwaresystems.Thedeficiencyofconventionalhardware.Schemeforthevirtualoscilloscopeforcomplexsignalswithsomerealtimeexperimentalresultsarepresentedinthiswork.Kevywords:Virtualinstrumentation,Chirpsignal,Dataacquisition,Triggering,Complexsignals,JTFA1.IntroductionForthelasttwodecadestherehasbeenatremendousprogressincomputertechnology.Measurementdomainisnolongerleftunaffected.Thewaymeasurementsarebeingdoneistotallyrevolutionized.Computerbasedmeasurementorsayvirtualinstrumentationisgraduallyreplacingthecostlybench2topinstrumentationasitoffersflexible,fastandcosteffectivesolutions.VariousclassicalinstrumentationsystemsnamelyOscilloscope,MultimetersandSpectrumanalyzersect.arealmostphasedoutbytheircounterpartvirtualinstrumentation.Ourresearchextendsthetrendanddemonstratesthedevelopmenofthecomputerbasedmixedsignaldigitaloscilloscope.Conventionalsignalssuchasthesinusoidshaveaconstantfrequencyandtheamplitedeonlyvarieswithtimethroughoutthesignaldefinition.Ontheotherhand,complexsignalscanbedefinedinthiscontextassignalsinwhichalltheparametersvary.Fig.1showsatypicalcomplexsignali.e.LinearChirp.Variationofamplitudeandfrequencywithtimecaneasilybeunderstoodbyhavingalookatthesignal.Thisrequiresavisuallystabledisplayofsignal.Thecomplexsignalofferschallengesf'oracquisition,displayananalysis.EventheconventionalmodernageDSOisnotcapableofdisplayingandanalyzingcomplexsignalsbecausetheseinstrumentsemploysimpletriggeringtechniquelikeleveltrigger.TheconventionaltechnniqueofvoltagetriggerapparentlyfailswhencomplexsignalslikechirpareanalyzedonDSO.Thisisduetotheveryfactthattheseinstrumentsconsiderchirpasaconventionalsinewaveandtriggerforeachcycleofthesinewaveinsteadoftriggeringforthecompletechirpcycle.ThisanalysisofthechirpsignalasseveralsinewaveformsofdifferentfrequenciesleadstheDSOtodisplaythemassinusoidsinquicksuccession.Asthisrapidchangeoccuesataveryhighrateandbecauseofhumaneyenotregisteringeventsoccurringfasterthan1/20thofasecondthedisplayappearsasseveraloverlappedsinewaves.Intherecentwork[1],anewtriggeringtechniquewasproposedforthecomplexsignalsbasedonWHD.Subsequentsectionspresentthesolutiontotheproblem.ForanalysisofthecomplexsignalsinfrequencydomainJFFAtechniqueisutilizedandimplemented[2-6].DSOusestheleveltriggertodisplaythewaveformappliedtoit.Thisleadstotriggerintervalandthenumberofsamplesforthistriggerintervaliscomputedandthesenumbersofsamplesaredisplay.TheDSOconsiderstheintervalasthefundamentaltimeperiodofthewholewaveformandthustakestbatmuchsamplesfromitsbufferandstartsdisplayingitinquicksuccession.Withsimplewaveformlikeasinewave,leveltriggercanachievestabledisplaybecausetriggerintervalcontainssamenumberofcycles.ThisisshowninFig.2a.34NowforthecomplexsignalasshowninFig.2b,leveltriggeringproducesatriggerintervalhavingvariablenumberofcyclesforthesamenumberofsamples/timeresultinginavisuallyunstabledisplay.TheactualtriggerintervalshouldbeonecompletecycleforachirpsignalasindicatedinFig.2c.Havingdonethistherepeatedchirpsignalforthistimedurationwillbedisplayedwithoutanyoverlappingcomponentsaslongastheentiretimeperiodisdisplayed.ToobservetheshortcomingsexperimentallyindisplayofcomplexsignalsontheoscilloscopeTektronixdualchannelsignalgeneratorAFG-3022(250MS/s,25MHz)wasusedtogenerateachirpsignalbychoosingthesweepmodetosinewaveformwithitsfrequencyvaryinglinearlywithrespecttotime.ThissignalwasfedtoTektronixTDS-2022(2GS/s,200MHz)dual-channelDSO.TheoverlappingdisplayasshowninFig.3wasobserved.2.IntelligentmethodoftriggeringAccuratetriggeringliessolelyoncorrectidentificationofthetimeperiodofwaveformunderconsideration.Forthispurpose,patternrecognitionschemewasimplementedtoidentifythepatterninthesignal[1]andthusobtainthetimeperiodofonecompletecycleofthechirp.First,a