lecroy 20_LTXXX-OM-E_Ch16 电路图.pdf

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1、LTXXX-OM-E Rev BISSUED: January2002211 CH A P T E RSI X T E E NHistogramParameters avgAverage Definition:Averageor meanvalueof datainahistogram. Description:Theaverageis calculatedbytheformula: Avg= = n 1i n 1 iiicount)(bin)(bin valuecount)(bin/ i , wherenis thenumber of bins in thehistogram, bincou

2、nt is thecount or height of a bin, andbinvalueis thecenter valueof therangeof parameter values abincan represent. Example: Value (volts) Count# 4.14.04.24.34.4 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Theaveragevalueof this histogram is: (4.1 * 2 + 4.3 * 3 + 4.4 * 1)/ 6 = 4.25. RadioFans.CN 收音机爱 好者资料库 H I S T

3、O G R A M S 212ISSUED: January2002LTXXX-OM-E Rev B fwhmFullWidthat HalfMaximum Definition:Determines thewidthof thelargest areapeak, measuredbetweenbins oneither side of thehighest bininthepeakthat haveapopulation of half thehighests population. If several peaks haveanareaequal tothemaximum populati

4、on, theleftmost peakis usedinthecomputation. Description:First, thehighest population peakis identifiedandtheheight of its highest bin (population)determined(for adiscussiononhowpeaks aredeterminedseethepks parameter Description:). Next, thepopulations of bins to theright andleft are found, until ab

5、inoneachsideis foundto haveapopulationof less than50% of that of thehighest bins. A lineis calculatedoneachside, from thecenter point of the first bin belowthe50% populationtothat of theadjacent bin, towards thehighest bin. Theintersection points of theselines withthe50% height valueis then determin

6、ed. Thelength of alineconnectingtheintersectionpoints is thevaluefor fwhm. Example: maximum 50% maximum fwhm 12 3 1 2 4 6 8 10 7 5 3 RadioFans.CN 收音机爱 好者资料库 CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002213 fwxxFullWidthat xx% Maximum Definition:Determines thewidth

7、of thelargest areapeak, measuredbetweenbins oneither side of thehighest bininthepeakthat haveapopulation of xx% of thehighests population. If several peaks haveanareaequal tothemaximum population, the leftmost peakis usedinthecomputation. Description:First, thehighest population peakis identifiedand

8、theheight of its highest bin (population)determined(seethepks Description:). Next, thebinpopulations tothe right andleft arefounduntil abin oneachsideis foundtohaveapopulation of less thanxx% of that of thehighest bin. A lineis calculatedoneachside, from thecenter point of thefirst binbelowthe50% po

9、pulationtothat of theadjacent bin, towards thehighest bin. Theintersection points of theselines withthexx% height valueis thendetermined. Thelengthof alineconnectingtheintersectionpoints is thevalue for fwxx. ParameterSettings:Selectionof thefwxxparameter inthe“CHANGE PARAM” menugroupcauses the“MORE

10、 fwxxSETUP” menutoappear. Pressingthecorrespondingmenu buttondisplays athresholdsettingmenuthat enables youtoset thexx valueto between0 and100% of thepeak. Example:fwxxwiththresholdset to35%: maximum 35% maximum fwhm 12 3 1 2 4 6 8 10 7 5 3 RadioFans.CN 收音机爱 好者资料库 H I S T O G R A M S 214ISSUED: Janu

11、ary2002LTXXX-OM-E Rev B hamplHistogramAmplitude Definition:Thedifferenceinvalueof thetwomost populatedpeaks inahistogram. This parameter is useful for waveforms withtwoprimaryparameter values, suchas TTL voltages, wherehamplwouldindicatethedifferencebetweenthebinary1 and0 voltagevalues. Description:

12、Thevalues at thecenter (linedividingthepopulationof peakinhalf)of thetwo highest peaks aredetermined(seepks parameter description:). Thevalueof the leftmost of thetwo peaks is thehistogram base(seehbase). Whilethat of the rightmost is thehistogram top(seehtop). Theparameter is thencalculatedas: hamp

13、l = htop hbase Example: peak #1 peak #2 hampl base top 152150 Inthis histogram, hamplis 152 mV 150 mV = 2 mV. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002215 HbaseHistogramBase Definition:Thevalueof theleftmost of thetwomost populatedpeaks inahistogram. This para

14、meter is primarilyuseful for waveforms withtwoprimaryparameter values such as TTL voltages wherehbase wouldindicatethebinary0 voltagevalue. Description:Thetwohighest histogram peaks aredetermined. If several peaks areof equal height theleftmost peakamongtheseis used(seepks). Then theleftmost of thet

15、wo identifiedpeaks is selected. This peaks center value(thelinethat divides the populationof thepeakinhalf)is thehbase. Example: hbase peak #1 peak #2 150 H I S T O G R A M S 216ISSUED: January2002LTXXX-OM-E Rev B highHigh Definition:Thevalueof therightmost populatedbininahistogram. Description:Ther

16、ightmost of all populatedhistogram bins is determined: highis its center value, thehighest parameter valueshowninthehistogram. Example: mV count 152 high Inthis histogram highis 152 mV. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002217 hmedianHistogramMedian Defini

17、tion:Thevalueof thex axis of ahistogram, dividingthehistogram populationintotwo equal halves. Description:Thetotal populationof thehistogram is determined. Scanningfrom left toright, the populationof eachbinis summeduntil abinthat causes thesum toequal or exceed half thepopulationvalueis encountered

18、. Theproportion of thepopulationof the binneededfor asum of half thetotal populationis thendetermined. Usingthis proportion, thehorizontal valueof thebinat thesameproportionof its rangeis found, andreturnedas hmedian. Example:Thetotal populationof ahistogram is 100 andthehistogram rangeis dividedint

19、o20 bins. Thepopulationsum, from left toright, is 48 at theeighthbin. Thepopulation of theninthbinis 8 andits sub-rangeis from 6.1 to6.5 V. Theratioof counts neededfor half- tototal-binpopulationis: 2 counts needed/ 8 counts = .25 Thevaluefor hmedianis: 6.1 volts + .25 * (6.5 6.1)volts = 6.2 volts H

20、 I S T O G R A M S 218ISSUED: January2002LTXXX-OM-E Rev B hrmsHistogramRoot MeanSquare Definition:Therms valueof thevalues inahistogram. Description:Thecenter valueof eachpopulatedbinis squaredandmultipliedbythepopulation (height)of thebin. All results aresummedandthetotal is dividedbythepopulation

21、of all thebins. Thesquareroot of theresult is returnedas hrms. Example:Usingthehistogram shownhere, thevaluefor hrms is: hrms = 4)/6*2.5+2*(3.5 22 = 2.87 value ount 2.53.5 1 2 3 4 CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002219 htopHistogramTop Definition:Thevalu

22、eof therightmost of thetwomost populatedpeaks inahistogram. This parameter is useful for waveforms withtwoprimaryparameter values, suchas TTL voltages, wherehtopwouldindicatethebinary1 voltagevalue. Description:Thetwohighest histogram peaks aredetermined. Therightmost of thetwo identifiedpeaks is th

23、en selected. Thecenter of that peakis htop(center is the horizontal point wherethepopulationtotheleft is equal totheareatotheright). Example: peak #1 peak #2 htop mV152 H I S T O G R A M S 220ISSUED: January2002LTXXX-OM-E Rev B lowLow Definition:Thevalueof theleftmost populatedbininahistogram popula

24、tion. It indicates the lowest parameter valueinahistograms population. Description:Theleftmost of all populatedhistogram bins is determined. Thecenter valueof that binis low. Example: mV count 150152140 Low Inthis histogram lowis 140 mV. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev B

25、ISSUED: January2002221 maxpMaximumPopulation Definition:Thecount (vertical value)of thehighest population bininahistogram. Description:Eachbinbetweentheparameter cursors is examinedfor its count. Thehighest count is returnedas maxp. Example: maxp Here, maxpis 14. H I S T O G R A M S 222ISSUED: Janua

26、ry2002LTXXX-OM-E Rev B modeMode Definition:Thevalueof thehighest populationbininahistogram. Description:Eachbinbetweentheparameter cursors is examinedfor its populationcount. The leftmost bin withthehighest count foundis selected. Its center valueis returnedas mode. Example: mV count 150 mode Here,

27、mode is 150 mV. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002223 pctlPercentile Definition:Computes thehorizontal datavaluethat separates thedatainahistogram suchthat thepopulationontheleft is aspecifiedpercentagexx of thetotal population. When thethresholdis set

28、to50%, pctlis thesameas hmedian. Description:Thetotal populationof thehistogram is determined. Scanningfrom left toright, the populationof eachbinis summeduntil abinthat causes thesum toequal or exceed xx% of thepopulationvalueis encountered. A ratioof thenumber of counts neededfor xx% population/to

29、tal binpopulationis thendeterminedfor thebin. Thehorizontal valueof thebinat that ratio point of its rangeis found, andreturned as pctl. Example:Thetotal populationof ahistogram is 100. Thehistogram rangeis dividedinto20 bins andxx is set to25%. Thepopulationsum at thesixthbinfrom theleft is 22. The

30、populationof theseventhis 9 andits sub-rangeis 6.1 to6.4 V. Theratioof counts neededfor 25% populationtototal binpopulationis: 3 counts needed/ 9 counts = 1/3. Thevaluefor pctlis: 6.1 volts + .33 * (6.4 6.1)volts = 6.2 volts. ParameterSettings:Selectionof thepctlparameter inthe“CHANGE PARAM” menugro

31、upcauses the “MORE pctl SETUP” menutoappear. Pressingthecorrespondingmenubutton displays athresholdsettingmenu. Withtheassociatedknobyoucanset the percentagevaluetobetween1% and100% of thetotal population. H I S T O G R A M S 224ISSUED: January2002LTXXX-OM-E Rev B pksPeaks Definition:Thenumber of pe

32、aks inahistogram. Description:Theinstrument analyzes histogram datatoidentifypeaks from backgroundnoise andhistogram binningartifacts suchas small gaps. Peakidentificationis a3-stepprocess: 1.Themeanheight of thehistogram is calculatedfor all populatedbins. A threshold(T1)is calculatedfrom this mean

33、where: T1= mean+ 2 sqrt (mean). 2.A secondthresholdis determinedbasedonall populatedbins under T1 in height, where: T2 = mean+ 2 * sigma, andwheresigmais thestandarddeviationof all populatedbins under T1. 3.OnceT2 is defined, thehistogram distributionis scannedfrom left toright. Any binthat crosses

34、aboveT2 signifies theexistenceof apeak. Scanningcontinues totheright until onebin or morecrosses belowT2. However, if thebin(s)cross belowT2 for less thanahundredthof thehistogram range, theyareignored, andscanningcontinues insearchof apeak(s)that crosses under T2 for more thanahundredthof thehistog

35、ram range. Scanninggoes onover theremainder of therangetoidentifyadditional peaks. Additional peaks withinafiftiethof therangeof thepopulatedpart of abinfrom aprevious peakareignored. NOTE: If the numberof bins is set toohigha histogrammayhave many smallgaps. This increases sigma and therebyT2, and

36、inextreme cases can prevent determinationof a peak, evenif one appears tobe present tothe eye. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002225 Example:Herethetwopeaks havebeenidentified. Thepeakwiththehighest populationis peak#1. T2 peak #1peak #2 H I S T O G R A

37、 M S 226ISSUED: January2002LTXXX-OM-E Rev B rangeRange Definition:Computes thedifferencebetweenthevalueof therightmost andthat of theleftmost populatedbin. Description:Therightmost andleftmost populatedbins areidentified. Thedifferenceinvalue betweenthetwois returnedas therange. Example: mV count 15

38、0 152 range Inthis example: range is 2 mV CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002227 sigmaSigma Definition:Thestandarddeviationof thedatainahistogram. Description:sigma is calculatedbytheformulas: mean=)/( n 1i n 1i iiicountbinbin value*countbin = ; sigma= )

39、/(1countbinmean)(bin value*countbin n 1i n 1i i 2 ii = , wherenis thenumber of bins in thehistogram, bincount is thecount or height of a bin, andbinvalueis thecenter valueof therangeof parameter values abincan represent. Example:For thehistogram: Value (volts) Count# 4.14.04.24.34.4 0 0.5 1.0 1.5 2.

40、0 2.5 3.0 3.5 mean= (2 * 4.1 + 3* 4.3 + 1 * 4.4)/ 6 = 4.25 sigma=(2*(4.1 - 4.25)+ 3*(4.3 - 4.25)+ 1*(4.4 - 4.25) ) / (6-1) 222 = 0.1225 H I S T O G R A M S 228ISSUED: January2002LTXXX-OM-E Rev B totpTotalPopulation Definition:Calculates thetotal populationof ahistogram betweentheparameter cursors. D

41、escription:Thecount for all populatedbins betweentheparameter cursors is summed. Example: Count 1 2 3 4 5 Thetotal population of this histogram is 9. CH A P T E RSI X T E E N:Histogram Parameters LTXXX-OM-E Rev BISSUED: January2002229 xapkX Coordinate ofxxthPeak Definition:Returns thevalueof thexxth

42、 peakthat is thelargest byareainahistogram. Description:First thepeaks inahistogram aredeterminedandrankedinorder of total area(for a discussionon howpeaks areidentifiedseetheDescription: for thepks parameter). Thecenter of thenthrankedpeak(thepoint wheretheareatotheleft is equal to theareatotherigh

43、t), wherenis selectedbyyou, is thenreturnedas xapk. Example:Therightmost peakis thelargest, andis thus rankedfirst inarea(1). Theleftmost peak, although higher, is rankedsecondinarea(2). Thelowest peakis alsothe smallest inarea(3). Largest-area peak 1 2 3 H I S T O G R A M S 230ISSUED: January2002LTXXX-OM-E Rev B BLANK PAGE