lecroy 93XXC-OM-E22 电路图.pdf

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1、? $SSHQGL?3DUDPHWHU?0HDVXUHPHQW 3DUDPHWHUV?DQG?+RZ?7KH?:RUN In this Appendix, a general explanation of how the instruments standard parameters are computed (see below) is followed by a table listing, defining and describing those parameters (page D5). Proper determination of the top and base referen

2、ce lines is fundamental for ensuring correct parameter calculations. The analysis begins by computing a histogram of the waveform data over the time interval spanned by the left and right time cursors. For example, the histogram of a waveform transitioning in two states will contain two peaks (Fig.

3、D1). 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 base reference levels: the top line corresponds to the top and the base line to the

4、 bottom centroid. Figure D1 HWHUPLQLQJ?7RS?DQG %DVH?/LQHV 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) RadioFans.CN 收音机爱 好者资料库 ? $SSHQGL? HWHUPLQLQJ?7LPH 3DUDPHWHUV O

5、nce top and base are estimated, calculation of the rise and fall times is easily done (Fig.1). The 90 % and 10 % threshold levels are automatically determined by the oscilloscope, using the amplitude (ampl) parameter. Threshold levels for rise or fall time can also be selected using absolute or rela

6、tive settings (rlevel, flevel). 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 lines is subdivided in

7、to a percentile scale (base = 0 %, top = 100 %) to determine the vertical position of the crossing points. The time interval separating the points 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 occu

8、r within the observation window. Rising Edge Duration() = Mr i ii TrTr Mr 1 1090 1 Falling Edge Duration() = Mf i ii TfTf Mf 1 9010 1 Where Mr is the number of leading edges found, Mf the number of trailing edges found, x i Trthe time when rising edge i crosses the x % level, and x i Tf the time whe

9、n 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. D2), located halfway (50 %) between the top and base reference lines. Time-parameter estimation depends on the number of cycles include

10、d within the observation window. If the number of cycles is not an integer, parameter measurements such as rms or mean will be biased. HWHUPLQLQJ?5LVH?DQG )DOO?7LPHV RadioFans.CN 收音机爱 好者资料库 ? 3DUDPHWHU?0HDVXUHPHQW HWHUPLQLQJ?LIIHUHQWLDO 7LPH?0HDVXUHPHQWV Figure D2 To avoid these bias effects, the in

11、strument uses cyclic parameters, including crms and cmean, that restrict the calculation to an integer number of cycles. The oscilloscope enables accurate differential time measurements between two traces for example, propagation, setup and hold delays (Fig. D3). Parameters such as c2d require the t

12、ransition polarity of the clock and data signals to be specified. RIGHT CURSOR LEFT CURSOR TWO FULL PERIODS: = 2cycles first last 50 % delay PERIODPERIOD cmean, cmedian, crms, csdev computed on interval periods widthwidthwidth freqperiod = 1/duty width/period= area, points, data computed between cur

13、sors TRIGGER POINT (Mesial) RadioFans.CN 收音机爱 好者资料库 ? $SSHQGL? Figure D3 Moreover, 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 th

14、e clock (trigger) from the first negative transition of the data signal. Similarly, c2d+ (1, 2) measures the time interval between the trigger and the next transition of the data signal. RIGHT CURSORLEFT CURSOR TRIGGER POINT DATA (1) CLK (2) THRESHOLD CLOCK EDGE = Positive Transition DATA EDGE = Neg

15、ative Transition HYSTERESIS Noisy spikes ignored due to Hysteresis band c2d (1, 2) c2d+(1, 2) ? 3DUDPHWHU?0HDVXUHPHQW 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLWLRQ1RWHV amplAmplitude: Measures difference between upper and lower levels in two-level signals. Differs from pkpk in that noise, overshoot, undershoo

16、t, and ringing do NOT affect measurement. top - base (See Fig. D1) On signals NOT having two major levels (such as triangle or saw-tooth waves), returns same value as pkpk. areaIntegral of data: Computes area of waveform between cursors relative to zero level. Values greater than zero contribute pos

17、itively to the area; values less than zero negatively. Sum from first to last of data multiplied by horizontal time between points (See Fig. D2) baseLower of two most probable states (higher is top). Measures lower level in two-level signals. Differs from min in that noise, overshoot, undershoot, an

18、d ringing do NOT affect measurement. Value of most probable lower state (See Fig. D1) On signals NOT having two major levels (triangle or saw- tooth waves, for example), returns same value as min. cyclesDetermines number of cycles of a periodic waveform lying between cursors. First cycle begins at f

19、irst transition after the left cursor. Transition may be positive- or negative-going. Number of cycles of periodic waveform (See Fig. D2) cmeanCyclic mean: Computes the average of waveform data. Contrary to mean, computes average over an integral number of cycles, eliminating bias caused by fraction

20、al intervals. Average of data values of an integral number of periods cmedianCyclic median: Computes average of base and top values over an integral number of cycles, contrary to median, eliminating bias caused by fractional intervals. Data value for which 50 % of values are above and 50 % below crm

21、sCyclic root mean square: Computes square root of sum of squares of data values divided by number of points. Contrary to rms, calculation performed over integral number of cycles, eliminating bias caused by fractional intervals. 1 2 1 N vi i N () = Where: v i denotes measured sample values, and N =

22、number of data points within the periods found up to maximum of 100 periods. ? $SSHQGL? 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLWLRQ1RWHV csdevCyclic standard deviation: Standard deviation of data values from mean value over integral number of periods. Contrary to sdev, calculation performed over integral nu

23、mber of cycles, eliminating bias caused by fractional intervals. = N i i )meanv( N 1 2 1 Where: vi denotes measured sample values, and N = number of data points within the periods found up to maximum of 100 periods. dataReturns average of all data points.All data values in analyzed region (See Fig.

24、D2) Multi-value parameter especially valuable for histograms and trends. delayTime from trigger to transition: Measures time between trigger and first 50 % crossing after left cursor. Can measure propagation delay between two signals by triggering on one and determining delay of other. Time between

25、trigger and first 50 % crossing after left cursor (See Fig. D2) dlydelay: Computes time between 50 % level of two sources. Time between midpoint transition of two sources tlvt at level: Computes transition between selected levels or sources. Time between transition levels of two sources, or from tri

26、gger to transition level of a single source Reference levels and edge- transition polarity can be selected. Hysteresis argument used to discriminate levels from noise in data. c2dclock to data : Computes difference in time from clock threshold crossing to either the next (c2d+) or previous (c2d) dat

27、a threshold crossing. Time from clock threshold crossing to next or previous edge (See Fig. D3) 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 expect

28、ed peakto peak value of signal and twice expected peaktopeak value of noise. ? 3DUDPHWHU?0HDVXUHPHQW 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLWLRQ1RWHV durFor single sweep waveforms, dur is 0; for sequence waveforms: time from first to last segments trigger; for single segments of sequence waveforms: time fro

29、m previous segments to current segments trigger; for waveforms produced by a history function: time from first to last accumulated waveforms trigger. Time from first to last acquisition for average, histogram or sequence waveforms dutyDuty cycle: Width as percentage of period. width/period (See Fig.

30、 D2) f8020%Fall 8020 %: Duration of pulse waveforms falling transition from 80% to 20%, averaged for all falling transitions between the cursors. Average duration of falling 8020 % transition On signals NOT having two major levels (triangle or saw-tooth waves, for example), top and base can default

31、to maximum and minimum, giving, however, less predictable results. flevelFall at level: Duration of pulse waveforms falling edges between transition levels. Duration of falling edge between transition levels On signals NOT having two major levels (triangle or saw-tooth waves, for example), top and b

32、ase can default to maximum and minimum, giving, however, less predictable results. Fall time: Measures time between two specified values on falling edges of a waveform. Fall times for each edge are averaged to produce final result. Arguments Threshold RemoteLower Limit Upper Limit Default Lowerlow1

33、%45 %10 % Upperhigh55 %99 %90 % fall Threshold arguments specify two vertical values on each edge used to compute fall time. Formulas for upper and lower values: lower valuelower threshold=+ amp base 100 upper valueupper threshold=+ amp base 100 Time at lower threshold - Time at upper threshold aver

34、aged over each falling edge (See Fig. D1) On signals NOT having two major levels (triangle or saw- tooth waves, for example), top and base can default to maximum and minimum, giving, however, less predictable results. ? $SSHQGL? 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLWLRQ1RWHV firstIndicates value of horizo

35、ntal axis at left cursor. Horizontal axis value at left cursor (See Fig. D2) Indicates location of left cursor. Cursors are interchangeable: for example, the left cursor may be moved to the right of the right cursor and first will give the location of the cursor formerly on the right, now on left. f

36、reqFrequency: Period of cyclic signal measured as time between every other pair of 50 % crossings. Starting with first transition after left cursor, the period is measured for each transition pair. Values then averaged and reciprocal used to give frequency. 1/period (See Fig. D2) lastTime from trigg

37、er to last (rightmost) cursor. Time from trigger to last cursor (See Fig. D2) Indicates location of right cursor. Cursors are interchangeable: for example, the right cursor may be moved to the left of the left cursor and first will give the location of the cursor formerly on the left, now on right.

38、maximum Measures highest point in waveform. Unlike top, does NOT assume waveform has two levels. Highest value in waveform between cursors (See Fig. D1) Gives similar result when applied to time domain waveform or histogram of data of same waveform. But with histograms, result may include contributi

39、ons from more than one acquisition. Computes horizontal axis location of rightmost non-zero bin of histogram not to be confused with maxp. meanAverage of data for time domain waveform. Computed as centroid of distribution for a histogram. But when input is periodic time domain waveform, computed on

40、an integral number of periods. Average of data (See Fig. D2) Gives similar result when applied to time domain waveform or histogram of data of same waveform. But with histograms, result may include contributions from more than one acquisition. ? 3DUDPHWHU?0HDVXUHPHQW 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLW

41、LRQ1RWHV medianThe average of base and top values.Average of base and top (See Fig. D2) minimumMeasures the lowest point in a waveform. Unlike base, does NOT assume waveform has two levels. Lowest value in waveform between cursors (See Fig. D1) Gives similar result when applied to time domain wavefo

42、rm or histogram of data of same waveform. But with histograms, result may include contributions from more than one acquisition. overOvershoot negative: Amount of overshoot following a falling edge, as percentage of amplitude. baseminimum ampl 16 100 (See Fig. D2) Waveform must contain at least one f

43、alling edge. On signals NOT having two major levels (triangle or saw-tooth waves, for example), may NOT give predictable results. over+Overshoot positive: Amount of overshoot following a rising edge specified as percentage of amplitude. maximumtop ampl 16 100 (See Fig. D1) Waveform must contain at l

44、east one rising edge. On signals NOT having two major levels (triangle or saw-tooth waves, for example), may NOT give predictable results. periodPeriod of a cyclic signal measured as time between every other pair of 50 % crossings. Starting with first transition after left cursor, period is measured

45、 for each transition pair, with values averaged to give final result. () = Mr i ii TrTr Mr 1 5050 1 (See Fig. D2) Where: Mr is the number of leading edges found, Mf the number of trailing edges found, x i Trthe time when rising edge i crosses the x % level, and x i Tf the time when falling edge i cr

46、osses the x % level. pkpkPeaktopeak: Difference between highest and lowest points in waveform. Unlike ampl, does not assume the waveform has two levels. maximum - minimum (See Fig. D1) Gives a similar result when applied to time domain waveform or histogram of data of the same waveform. But with his

47、tograms, result may include contributions from more than one acquisition. phasePhase difference between signal analyzed and signal used as reference. Phase difference between signal and reference pointsNumber of points in the waveform between the cursors. Number of points between cursors (See Fig. D

48、2) ? $SSHQGL? 3DUDPHWHU?DQG?ZKDW?LW?GRHVHILQLWLRQ1RWHV r2080%Rise 20 % to 80 %: Duration of pulse waveforms rising transition from 20% to 80%, averaged for all rising transitions between the cursors. Average duration of rising 2080 % transition On signals NOT having two major levels (triangle or saw

49、- tooth waves, for example), top and base can default to maximum and minimum, giving, however, less predictable results. rlevelRise at level: Duration of pulse waveforms rising edges between transition levels. Duration of rising edges between transition levels On signals NOT having two major levels (triangle or saw- tooth waves, for example), top and base can default to maximum and minimum, giving, however, less predictable results. Rise time: Measures time between two specified values on waveforms rising edge (1090 %). Rise times for each edge averaged to