lecroy 15_LTXXX-OM-E_Ch11 电路图.pdf

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1、144ISSUED: January2002LTXXX-OM-E Rev B CH A P T E REL E V E N:AnalyzewithParameters Part One introduced WaverunnerMeasure Tools. Nowuse theiradvanced aspects to troubleshoot and analyze yourwaveform. Inthis chapter, see how Tocustomize parameters ToperformPass/Failtests Parameters work Eachparameter

2、plays a specialrole inmeasurement RadioFans.CN 收音机爱 好者资料库 LTXXX-OM-E Rev BISSUED: January2002145 CH A P T E REL E V E NAnalyze withParameters UseCustomParameters 1.Press MEASURE TOOLS todisplaytheMEASURE menus. SeePart One, Chapter 4, “Choose a Measure Tool.” 2.Press thebuttontoselect Parameters, an

3、dthebuttonfor Custominthemodemenu. Usestatistics if desired, andset thestartingandendpoint for theparameter measurements usingthefrom andtomenus. 3.Then press thebuttontoselectandaccess theCHANGE PARAM menus. 4.Usethem tochangeyour parameters. Toselect aline, andtheparameter allocatedtoit, for modif

4、ication. Five lines withfiveuniqueparameters canbedisplayedandmodified. Toselect theparameter category. Todeleteall fiveassignedparameters from thelines. Toplaceanewparameter for measurement onthelineselectedabove. When “-” is selected, that lineis not used. Toselect thechannel or traceonwhichthepar

5、ameter will bemeasured. RadioFans.CN 收音机爱 好者资料库 PA R TTW O:L O O K I N GD E E P E R 146ISSUED: January2002LTXXX-OM-E Rev B CUSTOMIZE A PARAMETER Youcancustomizecertainparameters tomeet special needs: 1.Take, for example, timeat level, aparameter that computes thetransitionbetweendifferent levels of

6、a waveform, or betweendifferent sources. 2.Press thebuttontoselect theAllcategory, andthebuttontochoose t lvfrom themeasuremenu. 3.Turntheupper knob toset thenumber of sweeps: 4.Press thebuttontoselect channel or memoryTurntheknobfor fromandto. 5.Then press thebuttontoselect From theSETUP of tlv men

7、us thendisplayed: 6.Press thebuttontoset levels ineither absoluteor peak-to-peakpercent signal values: 7.Press thebuttontoset thehysteresis indivisions. This is avoltagebandthat extends equidistantlyabove andbelowtheselectedlevel. Inorder for thesignal to beconsideredvalid, andnot as noise, thesigna

8、l must exceed, or cross, theupper or lower limits of this bandbyhalf thehysteresis divisionsetting. 8.Turntheknobtoset thevoltageor amplitudepercent level inthe“from” menu. This determines whereonthewaveform Waverunner will start thetimingmeasurement. 9.Press thebuttontomakethemeasurement onapositiv

9、e(rising)or negative(falling)edge. Or, withFirst, tomakeit oneither edge. 10. Finally, turntheknob toset thevoltageor amplitudepercentageinthe“to” menu. This determines thelevel onthewaveform at whichthetimingis toend. 11. Press thebuttontoendthemeasurement onapositive(rising)or negative(falling)edg

10、e. Or, withFirst, to endit oneither edge. RadioFans.CN 收音机爱 好者资料库 CH A P T E REL E V E N:AnalyzewithParameters LTXXX-OM-E Rev BISSUED: January2002147 TestforPassandFail Youcanalsouseparameters tocarryout Pass/Fail tests. Theserequireacombinationof measurements within chosenlimits. TheWaverunner invo

11、kes anactionwhenthetest passes or fails dependingonwhat you specify. Youcanalsotest signals against atolerancemask. As withcustom parameters, youcanuseas manyas fiveparameters at thesametime. Whether thetests pass or fail, anyor all of thefollowingactions canbe invoked: Stopcapturingfurther signals

12、Dumpthescreenimagetoahardcopyunit Storeselectedtraces tointernal memory, toanoptional deviceinthePC Cardslot, or tofloppydisk Soundthebuzzer Emit apulsethroughtherear BNC connector Thedisplaywill showyoutheresults onthecurrent waveforms, thenumber of passingevents, thetotal number of sweeps treated,

13、 andtheactions for youtotake. SET UP A PASS/ FAIL TEST 1.Set upfor parameters intheMEASURE menuas showninChapter 4 andontheprecedingpages. 2.Press thebuttontoselect Pass or Failinthemodemenu. Usestatistics if desired, andset thestartingand endpoints for theparameter measurements usingthe“from” and“t

14、o” menus. 3.Then press thebuttontoselect From theCHANGE TEST menus displayed: 4.Pressthebuttontoset oneor moreof thefiveparameter lines. 5.Press thebuttontoselect Paramfrom theTest onmenufor testingusingthat parameter; “-” for notest. 6.Andpress thebutton toselect Paramfrom thechoosemenu. 7.Set theo

15、ther menus displayedas desired, accordingtothedescription on page145. 8.Thenif youwishtochangethePass/Fail test limit ontheparameter, press thebuttontoselect Limit from thechoosemenu. 9.Press thebuttontoselect theadequaterelation smaller or greater than from: PA R TTW O:L O O K I N GD E E P E R 148I

16、SSUED: January2002LTXXX-OM-E Rev B 10. Then press thebuttontoselect fromoneof threepossiblemodificationstothelimit. Thesearethelimits mantissa, exponent, andthenumber of digits to berepresentedinits mantissa. 11. Turntheknobtoset thevaluefor these. 12. Finally, press thebottom button to set thelimit

17、 tothelatest measuredvalue astartingvaluefor thefinal adjustment. PASS/ FAIL TEST ON A MASK 1.FollowtheCHANGE TEST Steps 1 to5 describedabove. 2.Press thebuttontoselect Maskfrom the“Test on” menufor testingusingthat parameter; “-” for no test. 3.Press thebuttontoselect themasktest conditionfrom 4.Pr

18、ess thebuttontoselect themasktest conditionfrom 5.Press thebuttontoselect thechannel or tracefor testingfrom theof menu, andthebuttonfor thetrace onwhichthemaskis tobeplacedfrom themaskmenu. N NO OT TE E: : Pass/Failtesting against a maskis affected byhorizontaland verticalzooming of the mask trace.

19、 The test willbe made inside the area bordered bythe parametercursors. Timebases of the mask and the trace undertest should be identical. Forvisualmasktesting, usea single grid whenperforming a masktest ona single trace; dual-grid displayfortesting ontwotraces. CH A P T E REL E V E N:AnalyzewithPara

20、meters LTXXX-OM-E Rev BISSUED: January2002149 MAKE A WAVEFORM MASK 1.Press thebuttontoselectfrom themaskCHANGE TEST menus describedabove. 2.Usethesemenus togenerateamaskfrom your waveform. Select Wformtogeneratethemaskfrom your displayedwaveform; Card todisplaymenus for recallingamaskstoredtoanoptio

21、nal deviceinthe PC Cardslot; Floppytorecall astoredmaskfrom floppydisk. Toselect D=M4if themaskis tobeautomaticallydisplayedonthe screen. Otherwiseselect M1, M2, M3, or M4. Usethe“RECALL WFORM” menus torecall anddisplayamemoryonatrace. Togenerateaninvertedmask. Toselect thewaveform tobeusedas theref

22、erence. Waverunner will generatethemaskaroundthis. Tomakethemask. Toselect thetoleranceinamplitudewiththeknob. Toselect thetoleranceintimewiththeknob. CHANGE A TEST ACTION 1.From theCHANGE TEST menus press thebuttonto select ActionintheOnline. 2.Press thebuttontodetermineif theactionwill betakenonPa

23、ss or Fail: 3.Press thebuttontoselect theactionin the“Then” menu. Andpress thebuttontoactivate(Yes)or disable (No)this actioninthefinal menu, nownamedfor theactionchosen. This yes or nois inturnshownin “Then.” PA R TTW O:L O O K I N GD E E P E R 150ISSUED: January2002LTXXX-OM-E Rev B HOWWAVE RUN N E

24、 RPARAME T E RSWORK Proper determination of the top and base reference lines is fundamental for ensuring correct parameter calculations. The analysis begins with Waverunner computing a histogram of the waveform data over the time interval spanned by the left and right time cursors. For example, the

25、histogram of a waveform transitioning in two states will contain two peaks (Fig. 1). The analysis will attempt to identify the two clusters that contain the largest data density. Then the most probable state (centroids) associated with these two clusters will be computed to determine the top and bas

26、e reference levels: the top line corresponds to the top and the base line to the bottom centroid. Once top and base are estimated, Waverunner easily calculates the rise and fall times. The oscilloscope automatically determines the 90% and 10% threshold levels, using the amplitude (ampl) parameter. (

27、Histograms are part of the WaveA nalyzer option.) RIGHT CURSORLEFT CURSOR risefall ampl pkpk width maximum top 50% (Mesial) HISTOGRAM* minimum base *not to scale Upper Threshold (90 % Amplitude) Lower Threshold (10 % Amplitude) Figure 1. Threshold levels for rise or fall time can also be selected us

28、ing absolute or relative settings (r level, f level). If absolute settings are chosen, the rise or fall time is measured as the time interval separating the two crossing points on a rising or falling edge. But when relative settings are chosen, the vertical interval spanned between the base and top

29、lines is subdivided into a percentile scale (base = 0%, top = 100%) to determine the vertical position of the crossing points. CH A P T E REL E V E N:AnalyzewithParameters LTXXX-OM-E Rev BISSUED: January2002151 Rising E dge Duration () = Mr i ii TrTr Mr 1 1090 1 The time interval separating the poin

30、ts on the rising or falling edges is then estimated to yield the rise or fall time. These results are averaged over the number of transition edges that occur within the observation window. Falling E dge Duration () = Mf i ii TfTf Mf 1 9010 1 Where Mr is the number of rising edges found, Mf the numbe

31、r of falling edges found, x i Trthe time when rising edge i crosses the x% level, and x i Tfthe time when falling edge i crosses the x% level. Time parameter measurements such as width, period and delay are carried out with respect to the mesial reference level (Fig. 2), located halfway (50%) betwee

32、n the top and base reference lines. Time parameter estimation depends on the number of cycles included within the observation window. If the number of cycles is not an integer, parameter measurements such as rms or mean will be biased. RIGHT CURSOR LEFT CURSOR TWO FULL PERIODS: cycles = 2 firstlast

33、50% delay PERIODPERIOD cmean, cmedian, crms, csdev computedon integral periods widthwidthwidth freq= 1/periodduty= width/period area, points, data computedbetween cursors TRIGGER POINT (Mesial) Figure 2. PA R TTW O:L O O K I N GD E E P E R 152ISSUED: January2002LTXXX-OM-E Rev B To avoid these bias e

34、ffects, the instrument uses cyclic parameters, including crms and cmean, that restrict the calculation to an integer number of cycles. The Waverunner enables accurate differential time measurements between two traces for example, propagation, setup and hold delays (Fig. 3). Parameters such asc2drequ

35、ire the transition polarity of the clock and data signals to be specified. RIGHT CURSORLEFT CURSOR TRIGGER POINT DATA (1) CLK(2) THRESHOLD CLOCK EDGE = PositiveTransition DATA EDGE = NegativeTransition HYSTERESIS Band Noisyspikes ignoreddue to Hysteresis band c2d-(1, 2) c2d+(1, 2) Figure 3. Moreover

36、, a hysteresis range may be specified to ignore any spurious transition that does not exceed the boundaries of the hysteresis interval. In Figure 3,c2d(1, 2) measures the time interval separating the rising edge of the clock (trigger) from the first negative transition of the data signal. Similarly,

37、c2d+(1, 2) measures the time interval between the trigger and the next transition of the data signal. CH A P T E REL E V E N:AnalyzewithParameters LTXXX-OM-E Rev BISSUED: January2002153 ChooseaParameter Thefollowingtablelists, describes anddefines Waverunner parameters. Thoseindicatedbythesymbol are

38、intheExtendedMathandWaveAnalyzer options (seeChapter 5, “Use a Math Tool”). All theother parameters listedherearestandardonWaverunner. PARAMETERDE SCRIPT IONDE FIN IT IONNOT E S amplAmplitude: Measures differencebetween upper and lower levels in two-level signals. Differs from pkpk inthat noise, ove

39、rshoot, undershoot, andringingdoNOTaffect measurement. topbase (SeeFig. 1) On signalsN OThaving two major levels (such as triangle or saw-tooth waves), returns same value as pkpk. areaIntegral of data: Computes areaof waveform between cursors relativetozero level. Values greater than zerocontribute

40、positivelytothearea; values less thanzero negatively. Sum from first to last of datamultiplied byhorizontal time betweenpoints (SeeFig. 2) baseLower of twomost probablestates (higher is top). Measures lower level intwo-level signals. Differs from minin that noise, overshoot, undershoot, andringingdo

41、NOT affect measurement. Valueof most probablelower state (SeeFig. 1) On signalsN OThaving two major levels (triangle or saw- tooth waves, for example), returns same value as min. cyclesDetermines number of cycles of aperiodic waveform lyingbetween cursors. First cycle begins at first transitionafter

42、 theleft cursor. Transitionmaybepositive- or negative- going. Number of cycles of periodic waveform (SeeFig. 2) cmeanCyclic mean: Computes theaverageof waveform data. Contrarytomean, computes averageover an integral number of cycles, eliminatingbias causedby fractional intervals. Averageof data valu

43、es of anintegral number of periods cmedianCyclic median: Computes averageof base andtopvalues over anintegral number of cycles, contraryto median, eliminatingbias causedbyfractional intervals. Datavaluefor which 50 % of values are aboveand 50 % below PA R TTW O:L O O K I N GD E E P E R 154ISSUED: Ja

44、nuary2002LTXXX-OM-E Rev B PARAMETERDE SCRIPT IONDE FIN IT IONNOT E S crmsCyclic root mean square: Computes square root of sum of squares of datavalues divided bynumber of points. Contraryto rms, calculation is performed over an integral number of cycles, eliminatingbias causedbyfractional intervals.

45、 1 2 1 N vi i N () = Where: videnotes measured sample values, andN =number of data points within the periods found up to maximum of 100 periods. csdevCyclic standarddeviation: Standard deviationof datavalues from meanvalue over integral number of periods. Contrary tosdev, calculation is performed ov

46、er an integral number of cycles, eliminatingbias causedbyfractional intervals. = N i i )meanv( N 1 2 1 Where: videnotes measured sample values, andN =number of data points within the periods found up to maximum of 100 periods. delayTimefrom trigger totransition: Measures timebetweentrigger andfirst

47、50% crossing after left cursor. Canmeasurepropagation delaybetweentwosignals bytriggeringon oneanddeterminingdelayof other. Timebetweentrigger andfirst 50% crossing after left cursor (SeeFig. 2) dlydelay: Computes timebetween 50% level of twosources. Timebetween midpoint transition of twosources t l

48、vt at level: Computes transition between selected levels or sources. Timebetween transitionlevels of twosources, or from trigger totransition level of asingle source Reference levels and edge- transition polarity can be selected. Hysteresis argument used to discriminate levels from noise in data. c2

49、d clockto data: Computes differencein timefrom clockthresholdcrossingto either thenext (c2d+)or previous (c2d)data thresholdcrossing. Timefrom clock threshold crossingto next or previous edge (SeeFig. 3) Threshold levels of clock and data signals, and edge transition polarity can be selected. Hysteresis argument used to differentiate peaks from noise in data, with good hysteresis value between half expected peak-to- peak value of signal and twice expected peak-to-peak value of noise. CH A P T E REL E V E N:AnalyzewithParameters LTXXX-OM-E Rev BISSUED: Jan