lecroy 09_LTXXX-OM-E_Ch5 电路图.pdf

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1、54ISSUED: January2002LTXXX-OM-E Rev B CH A P T E RFI V E:UseMathTools Inthis chapter, see how Toset upformath Todomultiplication ToperformanFFT Todosummed averaging Tostore and recallwaveforms Toobtaina waveformormemorystatus report RadioFans.CN 收音机爱 好者资料库 LTXXX-OM-E Rev BISSUED: January200255 CH A

2、P T E RFI V EUseMathTools MakeMathEasy WithWaverunner mathtools youcanperform mathematical functions onawaveform displayedonany channel, or recalledfrom anyof thefour referencememories M1, M2, M3, or M4. Todocomputations in sequence, youcanalsoset upanytraceof A, B, C, or D for math. For example: yo

3、ucouldset upTraceA as thedifferencebetweenChannels 1 and2, TraceB as theaverageof A, andTraceC as theintegral of B. Youcouldthendisplaytheintegral of theaverageddifferencebetween Channels 1 and2. Anytraceandfunctioncan bechainedtoanother traceandfunction. For example, youcould makeTraceA anaverageof

4、 Channel 1, TraceB anFFT of A, andTraceC azoom of B. Waverunner mathtools areavailableinthesestandardandoptional packages: ArithmeticSum (add), Difference(subtract), Product (multiply), Ratio(divide) AveragingSummed(linear)Averageof upto1000 sweeps Extrema (envelope) FFTFast Fourier Transform to50 0

5、00 points; Power Spectrum, Phase, Magnitude; All FFT Windows FunctionsIdentity, Negation, (Sinx)/x Resample (deskew) Rescale ST AN DARD MAT H Included with all Waverunner oscilloscopes Enhanced Resolution(ERES) Functions AbsoluteValue, Derivative, Exp(basee), Exp(base10), Integral, Log(basee), Log(b

6、ase10), Ratio, Reciprocal, Square, SquareRoot EXT E N DE D MAT H AN D ME ASURE ME N T OPT ION(E MM) A ll tools in Standard Math plus: Trending AveragingSummed, or linear, Averageof uptoonemillionwaveforms; Continuous Average FFT+Fast Fourier Transform to onemillion points; FFT Average; Power Averagi

7、ng, Power Density, Real, Real + Imaginary WAVEAN AL YZE R OPT ION (WAVA) A ll tools in E xtended Math plus: HistogramsHistograms, Histogram Parameters RadioFans.CN 收音机爱 好者资料库 PA R TON E:G E T T I N GS T A R T E D 56ISSUED: January2002LTXXX-OM-E Rev B SET UP TO DO WAVEFORM MATHEMATICS After connectin

8、gyour signal toaWaverunner channel (Channel 1 in this example), dothefollowing: 1.Press 1 toselect CHANNEL 1 anddisplayWaverunners basic menus. 2.Pressto 3.Press A tomakeTraceA azoom of Channel 1. 4.Press thebuttonfor 5.Press thebuttontoselectanddisplaytheSETUP OF A menus, shown next page. TOSE TUP

9、FORMAT HAN OT H E RWAY First.Press MATH TOOLS to display the ZOOM + MA TH menus. Second.Selector one of the other traces. Third.Press thebuttonto select Fourth.Follow the first three steps in the procedure above. N NO OT TE E: : A waveform processing title foreach displayed trace willbeshown inits t

10、race label. If the title is missing, the mathfunction cannot be done and the contents of the trace will remainunchanged. RadioFans.CN 收音机爱 好者资料库 CH A P T E RFI V E:UseMathTools LTXXX-OM-E Rev BISSUED: January200257 USE A MATH TOOL Usethesemenus tochooseandset upanymathtool. As anexample, select thea

11、rithmetic tool Product to multiplyChannel 1 byChannel 2. Toenablemath. 6.Press toselect Arithmetic. 7.Press toselect Product. 8.Press toselect Channel 1 as thesourcetrace. When usingArithmetic, this sets oneof thetwo operand sources. Usingother mathtypes, this menumaybeina different positionandmayse

12、t thesignal offset, number of sweeps, or compensatefor anyDC offset inthe signal. 9.Press toselect thetracebywhichthesourcetrace Channel 1 will bemultiplied. Nowgoontoset upyour traceas anFFT (Fast Fourier Transform)function(next page). PA R TON E:G E T T I N GS T A R T E D 58ISSUED: January2002LTXX

13、X-OM-E Rev B PERFORM AN FFT OPERATION Continuingfrom theprecedingsteps, set upChannel 1 for FFT. Fast Fourier Transform will convert your time domainwaveform intoafrequencydomainspectrum similar tothat of anRF spectrum analyzer display. But unliketheanalyzer, whichhas controls for spanandresolutionb

14、andwidth, withWaverunner youdeterminethe FFT spanusingthescopes samplingrate(seeChapter 10, “Use Advanced Math Tools”). 10. Pressthebuttontoselect FFT fromtheMathTypemenu. Spectrawill beshownwithalinear frequencyaxis runningfrom zero to theNyquist frequency. Thefrequencyscalefactors (Hz/div)areina 1

15、25 sequence. Theprocessingequationis displayedat thebottom of thescreen, together withthethreekeyparameters that characterizean FFT spectrum: T TI IP P: : During FFT computation, the FFT signis shownbelow the grid. The computationcan take a while onlong time- domainrecords, but you can stopit at any

16、time bypressing anyfront panelbutton. Transform sizeN (number of input points) Nyquist frequency(= samplerate) Frequencyincrement, f, betweentwosuccessivepoints of thespectrum. Theseparameters arerelatedas: Nyquist frequency= f N/2, wheref = 1/T, andT is thedurationof theinput waveform record(10 tim

17、e/div). Thenumber of output points is equal toN/2. 11. Press thebuttontoselect Power Spectrum from themenu PowerSpectrumis thesignal power, or magnitude, representedonalogarithmic vertical scale: 0 dBm corresponds tothevoltage(0.316 V peak), whichis equivalent to1 mW into50 . Power Spectrum is suita

18、blefor characterizingspectrathat containisolatedpeaks (dBm). Other FFT functions availablein this menudependontheWaverunner mathoptions installedinyour scope (seepage55). CH A P T E RFI V E:UseMathTools LTXXX-OM-E Rev BISSUED: January200259 Phase is measuredwithrespect toacosinewhosemaximum occurs a

19、t theleft-handedgeof thescreen, at which point it has 0. Similarly, apositive-goingsinewavestartingat theleft-handedgeof thescreenhas a 90 phase. Phaseis displayedindegrees. PowerDensity: Signal power normalizedtothebandwidthof theequivalent filter associatedwiththeFFT calculation. Suitablefor chara

20、cterizingbroadbandnoise. Power Densityis displayedonalogarithmic vertical axis calibratedindBm. It is availableonlywiththeWaveAnalyzer optionfor theWaverunner. Magnitude: Thepeaksignal amplitudeis representedonalinear scale, inthesameunits as theinput signal. Real, Real+ Imaginary, Imaginary: Comple

21、xresult of theFFT processinginthesameunits as theinput signal. TheseareonlyavailablewiththeWaveAnalyzer option. 12. Nowturntheknobtoselect VonHannandpress thebuttonto select AC. AC forces theDC component of theinput signal to zerobeforeFFT processing, andimproves theamplitude resolution. This is esp

22、eciallyuseful whenyour input has alargeDC component. FFT windows definethebandwidthandshapeof theFFT filter. (SeeChapter 10, “Use Advanced Math Tools,” for thewindows filter parameters.) VonHann(Hanning)windows reduceleakageandimproveamplitudeaccuracy. But theyalsoreduce frequencyresolution. Rectang

23、ularwindows shouldbeusedwhen thesignal is transient (completelycontainedinthetime-domain window)or youknowit to haveafundamental frequencycomponent that is aninteger multipleof the fundamental frequencyof thewindow . Other signal types will showvaryingamounts of spectral leakageand scalloploss wheny

24、ouuseaRectangular window . Tocorrect this, useanother windowtype. Hamming reduces leakageandimproves amplitudeaccuracy, but alsoreduces frequencyresolution. Flat Topprovides excellent amplitudeaccuracywithmoderateleakagereduction, but alsoreduces frequency resolution. BlackmanHarris windows reducele

25、akagetoaminimum, but reducefrequencyresolution. 13. Inthefinal FFT step, press thebuttontoselect thesourcetrace. The“before” and“after” of your FFT computationis shownonthenext page. PA R TON E:G E T T I N GS T A R T E D 60ISSUED: January2002LTXXX-OM-E Rev B FFT Power Spectrum: The top grid shows th

26、e waveform in the time domain, while the bottom one shows it in the frequency domain, after FFT Power Spectrum has been applied. With the cursor measure tool (positioned here on the left-most peak of the FFT trace) you can read either the time or frequency of your waveform. Trace As label indicates

27、2 MHz per division in the frequency domain. The memory status field beneath the grids gives other FFT information. CH A P T E RFI V E:UseMathTools LTXXX-OM-E Rev BISSUED: January200261 DO SUMMED AVERAGING NowmakeaSummedAverageof your waveform again, goingonfrom theprevious steps. Averagingis normall

28、yusedtoeliminatenoise. 14. Pressthebuttontoselect AveragefromtheMathTypemenu. 15. Press thebuttontoselect Waverunner starts thecalculationimmediately. 16. Turntheupper knob toset thenumber of sweeps(up to4000) This is countedinthetracelabel, as shownhere, at right: If theoptional Continuous Averagei

29、s selected, the“for” menubecomes “withweighting”. Useit todefinetheweight. (SeeChapter 10, “Use Advanced Math Tools,” for thedifferencebetween summedandcontinuous averaging.) 17. Finally, press thebutton toselect thesourcetrace: Thetypeof result youcanexpect isillustratedonthenext page. PA R TON E:G

30、 E T T I N GS T A R T E D 62ISSUED: January2002LTXXX-OM-E Rev B Summed A verage: N oise evident in the signal shown in the top trace has been eliminated from the averaged waveform on the lower grid. The calculation was stopped after 206 sweeps. The number of points used in the calculation is shown i

31、n the information field at the bottom of the screen. The same number of points means that all points were used in the calculation. CH A P T E RFI V E:UseMathTools LTXXX-OM-E Rev BISSUED: January200263 SaveandRecallWaveforms Saveyour waveforms tointernal referencememory M1, M2, M3 or M4 or tofloppydi

32、skor theoptional PC Cardslot (Memorycardor HDD). Recall them later for further analysis. Youcouldzoom them or perform moremath. 1.Press WAVE STORAGE andthenthebuttonfor N NO OT TE E: : Foreachunit of record lengthperchannel, orperzoom and mathtrace, a point canbe stored inthe waveformreference memor

33、ies M1, M2, M3, orM4. 2.Usethesemenus tostoreyour displayedwaveform. Tostorethewaveform, whichyoufirst select from themenubelow , to thememoryor floppydisk(also selectedbelow). Toselect thechannel or tracewhosewaveform youwishto store. Toselect theinternal referencememory, floppy, or optional storag

34、edevicethewaveform is tobesavedto. SeeChapter 12, “Use Waverunner with PC,” for how tosavewaveforms inASCII format. RETURN 3.Press togobacktothe“WFORM” menus in order torecall the waveform youhavestored. PA R TON E:G E T T I N GS T A R T E D 64ISSUED: January2002LTXXX-OM-E Rev B 4.Pressthebuttonfor

35、5.Thesemenus will bedisplayed. Usethem torecall your waveform. Torecallthewaveformfrommemoryor portablestoragedevice. Torecall theselectedwaveform totheselectedtrace(seemenus below). Toselect thememoryinwhichthewaveform youwishto displayis stored. Toselect thetraceonwhichtherecalledwaveform is to be

36、 displayed. T TI IP P: : Transferwaveformdata toPC and use the data forcalculations withspreadsheet ormath software. Todothis, save yourwaveforms tofloppyoranoptionalstorage device inthe ASCII format. WaverunnercansavetofloppyinASCII traces of upto50000points. You should rememberthat waveforms store

37、d inASCII cannot be called backintothe oscilloscope. See Chapter12, “Use WaverunnerwithPC.” CH A P T E RFI V E:UseMathTools LTXXX-OM-E Rev BISSUED: January200265 OBTAIN A WAVEFORM OR MEMORY STATUS REPORT Displayasummaryof thestatus of your channels, zoom andmathfunctions, waveform memories, and disp

38、layedtraces. Viewthesettings onyour vertical andhorizontal controls. Checkonhowmuchmemoryyour Waverunner scopeis usingfor storageof records. Clear andfreeupmemory. 1.Press SCOPE STATUS toshowtheSTATUS menus. 2.Press thebuttontoselect Waveformandthebuttonfor thewaveform status summaryof choice. 3.Press thebuttontoselect MemoryUsed toobtainasimilar report on what youhavestoredandhow muchmemoryis available. Memories occupiedbywaveforms will beboxed, andemptyones indicatedas such. Youcanalsoclear occupiedmemories bypressingthecorrespondingmenubuttons.