lecroy 17_LTXXX-OM-E_Ch13 电路图.pdf

LTXXX-OM-E Rev BISSUED: January2002175 P P A AR RT T T T HHR RE E E E WWA AV V E E A AN N A AL L Y YZ Z E E R R ( (WWA AV V A A OO P PT T I I OO N N ) ) RadioFans.CN 收音机爱 好者资料库 176ISSUED: January2002LTXXX-OM-E Rev B CH A P T E RT H I R T E E N:Parameters Inthis chapter, see how Toset upforhistograms RadioFans.CN 收音机爱 好者资料库 LTXXX-OM-E Rev BISSUED: January2002177 CH A P T E RTH I R T E E NParameters AValuableToolforWaveformAnalysis TheWaveAnalyzer optionaddedtoyour Waverunner oscilloscopeprovides avaluabletool for dataanalysis and theinterpretation of measurement results: thehistogram. With WAVA, histograms of waveform parameter measurements canbecreated, statistical parameters determined, andgraphic features quantifiedfor analysis. Statistical parameters suchas mean, standarddeviationandmedianareextremelyuseful, but aloneare usuallyinsufficient for determining whether measureddatadistributionis as expected(seeChapters 4 and 11). Histograms expandtheuseof parameters toenhanceyour understandingbyofferingvisual assessment of this distributionandrevealing: distributiontype, suchas normal or non-normal, helpful for determiningwhether thesignal behaves as expected; distributiontails and extreme values, which canbeobserved, andwhichmayberelatedtonoiseor other infrequent andnon-repetitivesources; and multiple modes, observableandpossiblyindicativeof multiplefrequencies or amplitudes, whichcanbe usedtodifferentiatefrom other sources suchas jitter andnoise. SET UP FOR HISTOGRAMS Histograms arebasedon settings that includebinwidthandnumber of parameter events. TheWaverunner scopewith WAVA uses special parameters for determininghistogram characteristics suchas mean, median, standarddeviation, number of peaks andmost populatedbin. But beforeyoucancreateahistogram, youmust first set uptheparameters youhavechosen: 4.Press MEASURE TOOLS todisplaytheMEASURE menus. 5.Press thebuttontoselect Parameters, andthebuttonfor Useif desired. 6.Set start andendpoints for themeasurements withand RadioFans.CN 收音机爱 好者资料库 PA R TI I I:WA V EAN A L Y Z E R 178ISSUED: January2002LTXXX-OM-E Rev B Parameters areusedtoperform waveform measurements for thesectionof awaveform lyingbetweenthe parameter cursors (Fig. 1.1, item ). Thepositionof theparameter cursors is set usingthefromandtomenus, andcontrolledbytheassociatedmenuknobs. Thetoptraceinthefigurebelowshows asinewaveon whicha freq parameter measurement ()is beingperformed, withavalueof 202.442 kHz as theaveragefrequency. Thebottom traceshows ahistogram of this parameter andavalueof 201.89 kHz () theaverage frequencyof thedatacontainedwithintheparameter cursors. 1 2 3 Figure1.1 4.Press thebuttontoselectandaccess theCHANGE PARAM menus. CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002179 As showninFigure1.2, uptofiveparameters cannowbeselected, eachdisplayedonits ownlinebelowthe grid. Categories areprovidedfor relatedgroups of parameter measurements. Thefreqmeasureparameter from the“Cyclic” categoryfor Trace1, previouslyselected, is displayedonLine1 as freq(1) (Item ). Theavg measureparameter from the“Statistics” categoryfor TraceA is displayedonLine2. This categoryprovides histogram parameters, whileavgoffers themeanvalueof theunderlyingmeasurements for theTraceA histogram section withintheparameter cursors (), shownas “avg(A)” in. Additional parameter measurements canbeselectedfrom “Category” and“measure”. Noparameters havebeenselectedfor Lines 3 to5 5.After selectingacategory, chooseaparameter from the“measure” menu. Thenselect theparameter displaylinefrom the“Online” menu. 1 3 2 Figure1.2 If aparameter has additional settings that youmust supplyinorder toperform measurements, theMORE xxxx SETUP menuappears. But if noadditional settings arerequiredtheDELETE ALL PARAMETERS menuappears, as shownhere: pressingtheassociatedmenubuttonclears theresults inall fivelines of parameters. PA R TI I I:WA V EAN A L Y Z E R 180ISSUED: January2002LTXXX-OM-E Rev B PARAME T E R-VAL UECAL CUL AT ION AN DDISPL AY Whenyouarenot usingpersistence,thedisplayforinput channelsshowsthecapturedw aveformof asingle sweep.Fornon-segm entedw aveform s,thedisplayisidentical toasingleacquisition.But withsegm ented w aveform s,theresult of asingleacquisitionforall segm entsisdisplayed. Thevaluedisplayedforachosenparam eterdependsonw hether“statistics” isonoroff.Andonw hetherthew aveformis segm ented.Thesetwofactorsinadditiontotheparam eterchosendeterm inew hetherresultsareprovidedforasingleacquisition (trigger)orm ultipleacquisitions.Ineithercase, onlythew aveformsectionbetweentheparam etercursorsisused. If thew aveformsourceisam em ory(M1,M2,M3, orM4)thenloadinganeww aveformintom em oryactsasatriggerand sweep. Thisalsoappliesw henthew aveformsourceisazoomof aninput channel,andw henanewsegm ent orthe“All Segm ents” m enuisselected. With“statistics” off,theparam eterresultsforthelast acquisitionaredisplayed. Thiscorrespondstoresultsforthelast segm ent for segm entedw aveform swithall segm entsdisplayed.Forzoomtracesof segm entedw aveform s,selectionof anindividual segm ent gives theparam etervalueforthedisplayedportionof thesegm ent betweentheparam etercursors.Selectionof “All Segm ents” provides theparam eterresultsfromthelast segm ent inthetrace. With“statistics” on,andw heretheparam eterdoesnot usetwow aveform sincalculatingaresult (dly,t lv),resultsareshown forall acquisitionssincetheCLEAR SWEEPS buttonw aslast pressed.If theparam eterusestwow aveform s,theresult of com paringonlythelast segm ent persweepforeachw aveformcontributestothestatistics. Thestatisticsfortheselectedsegm ent aredisplayedforzoomtracesof segm entedw aveform s.Selectionof anewsegm ent or“All Segm ents” actsasanewsweepandtheparam etercalculationsforthenewsegm ent(s)contributetothestatistics. Dependingontheparam eter,singleorm ultiplecalculationscanbeperform edforeachacquisition.Forexam ple,theperiod param etercalculatesaperiodvalueforeachof uptothefirst 50cyclesinanacquisition. Whenm ultiplecalculationsare perform ed,with“Statistics”Offtheparam eterresult showstheaveragevalueof thesecalculations. WhereasOndisplaysthe average,low ,high,andsigm avaluesof all thecalculations. CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002181 InFigure1.3,below ,theuppertraceshowsthepersistencedisplayof asignal. Theinitial suggestionisof frequencydrift inthe signal source.Thelowertraceshowsahistogramof thefrequencyasm easuredbytheoscilloscope. Figure1.3 Thishistogramindicatestwofrequencydistributionswithdom inant frequenciesseparatedby4000Hz.Therearetwodistinct and norm al lookingdistributions,without widevariation, withineachof thetwo.Wecanconcludethat therearetwodom inant frequencies.If theproblemwererelatedtofrequencydrift,thedistributionwouldhaveatendencytobebroader,non-norm al in appearance,andnorm allytherewouldnot betwodistinct distributions. Afterabrief visual analysis,them easurem ent cursorsandstatistical param eterscanbeusedtodeterm ineadditional characteristics of distribution,includingthem ost com m onfrequencyineachdistributionandthespreadof eachdistribution. PA R TI I I:WA V EAN A L Y Z E R 182ISSUED: January2002LTXXX-OM-E Rev B Figure1.4,below ,showstheuseof them easurem ent cursor(Item),todeterm inethefrequencyrepresentedbyonebinof the distribution. Thevalueof thebin,insidetheDisplayedTraceFieldisindicatedby. 12 Figure1.4 CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002183 Figure1.5,below ,showstheuseof theparam etercursors(Item sand)indeterm iningtheaveragefrequencyof the distributionlocatedbetweenthecursors. Theaveragevalueof them easurem entsintheright-handdistributionisindicatedby. 1 3 2 Figure1.5 PA R TI I I:WA V EAN A L Y Z E R 184ISSUED: January2002LTXXX-OM-E Rev B Finally,Figure1.6showstheuseof them easurem ent cursors(Item sand)indeterm iningthedifferenceinfrequencybetween abininthecenterof eachdistribution.ThevalueinkHz,intheDisplayedTraceField,isindicatedby. 1 3 2 Figure1.6 CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002185 ParameterMath LeCroys WaveAnalyzer optionalsogives youtheabilityto perform arithmetic operations (addition, subtraction, multiplication, division)ontheresults of twoparameter measurements. Bycustomizingparameters inthis way, youcaneffectivelyextendtherangeof parameter measurements basedonyour particular needs. For example, supposeyouneedtomeasurethecrest factor of awaveform. Traditionally, youwouldselect the peak-to-peakandrms parameters, thenmanuallycomputetheratio of peak-to-peaktorms. Figure1.7, on the other hand, shows howparameter math was usedtoconfigurecrest factor as acalculatedparameter. Thelist of custom parameters comprises 5 calculatedparameters labeledcalc1throughcalc5. Figure1.7.Calculatedparam etersallowthecreationof customparam eters.Herecalc1isset uptom easurecrest factor(peak-to- peak/ rm s). Selectingthecalculatedparameter calc1from themeasure parameter menuallows youtoset it up, as shown inFigure1.8. Heretheparameters, sourcewaveforms, andarithmetic operator canbeselected. Thecalc1 parameter has beenset uptodisplaytheratioof peak-to-peaktorms for channel 2. This is showninthe calc1 summaryboxunder thegrid. PA R TI I I:WA V EAN A L Y Z E R 186ISSUED: January2002LTXXX-OM-E Rev B Figure1.8.DefiningCalc1toReadtheCrest Factorof Channel 2 Thefivecalculatedparameters computenewparameters basedonanytwoparameters operatingonany combinationof theacquisitionchannels or math/zoom traces. Thesourceparameters donot haveto be displayed. Figure1.9 is anexampleof settingupadirect measurement of themodulationindexof anFM signal. Phase modulationhas beenperformedusingtheJitterTrack of timeinterval error (TIE)of theinput signal from channel 2. Differentiationandrescalingconvert theTIE functionintothedemodulatedFM signal. TheTIE functionis multipliedbythecarrier frequencyof 400 MHz. This results inadisplayof frequencydeviation versus time. Becausetheratio of 1/2thepeak-to-peakfrequencydeviationis requiredfor theFM modulation index, TIE must alsobedividedby2. All this is doneinTraceD, usingtherescalefunctiontomultiplyby2*E8 (400 MHz/2). Ingeneral, all additiveor multiplicativeconstant operations inthecalculatedparameters require therescalefunction. (Inthis exampletherescaleoperationwas requiredanyway.) Figure1.10 shows thesetupof calculatedparameter calc5toreadtheFM modulationindexbytaking1/2the peak-to-peakfrequencydeviationdividedbythemodulationfrequency. Both parameters arederivedfrom traceD. CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002187 Figure1.9.UsingRescalingtoConvert TIE toaDisplayof FrequencyDeviation Figure1.10.SettingCalc5toMeasureFM ModulationIndex PA R TI I I:WA V EAN A L Y Z E R 188ISSUED: January2002LTXXX-OM-E Rev B LOGARITHMIC PARAMETERS TheParameter Mathoption prevents multiplicationanddivision of parameters that returnlogarithmic values. Theseparameters areas follows: auto-correlationsignal-to-noiseratio(ACSN) narrow-bandpower (NBPW) mediasignal-to-noiseratio(MSNR) residual signal-to-noiseratio(RSNR) top-to-baseratio whentheunits areindB (TBR) EXCLUDED PARAMETERS Parameters that arealreadytheresult of parameter mathoperations areexcluded, andwill not appear inthe parameter menu. If theyareincludedinaremotecontrol setupcommand, anerror messageis generatedand thesetupcanceled. Excludedparameters areas follows: beginningedgeshift (BES) beginningedgeshift list (BES) beginningedgeshift sigma(BESS) beginningedgeshift sigma list (BESS) deltaclock-to-datanear (DC2D) deltaclock-to-datanext (DC2DPOS) deltaclock-to-dataprevious (DC2DNEG) deltadelay(DDLY) deltapit-to-clock(DP2C) deltapit-to-clock list (DP2C) deltapit-to-clocksigma(DP2CS) deltapit-to-clocksigma list (DP2CS) deltatimeat level (DTLEV) endedgeshift (EES) endedgeshift list (EES) endedgeshift sigma(EESS) endedgeshift sigma list (EESS) phase(PHASE) resolution(RES) apparent power (APWR) mTnTmT shift (BEES) mTnTmT shift sigma(BEESS) mTnTmT shift sigma list (BEESS) power factor (PF) real power (RPWR) CH A P T E RTH I R T E E N:Parameters LTXXX-OM-E Rev BISSUED: January2002189 TO SET UP PARAMETER MATH 1.Press MEASURETOOLS. 2.Press thebuttonfor Parameters. TheMEASURE menupanel appears. 3.From themode menu, select Custom. 4.Press thebuttonfor ChangeParameters. TheCHANGE PARAM menupanel appears. 5.From theOnline menu, select theline(1through5)belowthegridonwhichyouwant to showthe calculationresult. 6.From theCategory menu, select All. 7.From themeasure menuselect, calcx (calc1throughcalc5). 8.Press thebuttonfor MoreCalcx Setup. TheSETUP CALCx menupanel appears. 9.If thecurrent calc parameter is alreadydefinedandyouwant toredefineit, press thebuttonfor CLEAR THIS PARAMETER. 10. From theOperation menu, select anarithmetic operator (+, ,*, /). 11. Toset thefirst parameter intheequation, select Param1from theSelect menu. Thenchoosea parameter from theParameter menu. 12. Set thesecondparameter intheequationbyselectingParm2from theSelect menu. Thenchoosea parameter from theParameter menu. PA R TI I I:WA V EAN A L Y Z E R 190ISSUED: January2002LTXXX-OM-E Rev B BLANK PAGE