Teledyne LeCroy WavePro Automation Command - Manual (Page 299)

Automation Command and Query Reference Manual - Control Reference
JitterModel Enum
Most jitter measurements are extrapolated to probability 10e-12, as if we had seen at least one trillion
UI. In order to extrapolate, jitter must be decomposed into DJ, which does not grow as more UI are
observed, and RJ, which does. How much of the jitter is attributed to Rj therefore affects the value of
Tj. In most cases, the Jitter Model choice is not significant. Our default is Spectral. But in some
cases NQ Scale might be preferred.
There is a discussion of NQ Scale in the description of
app.SDA2.JitterMeasure.Histogram.ShowNQScaleFit.
Q scale is a coordinate transformation of the CDF (see ShowLogCDF) such that for a Gaussian
distribution, the Q scale lines should be straight, with a slope of 1/sigma (note: sigma is Rj), and
intercept with Q = 0 (the top of the grid) at the mean of the Gaussian. If there is only one Guassian
(no DJ) then the left and right sides include the entire populiation, that is, they sum to a total probability
of 1.
NQScale is Normalized Q Scale; it is normalized to allow the left and right side tails to have arbitrary
total probability. If more than one Gaussian is present (that is, if DJ is not zero) then the NQScale fit
lines on the left and right will intersect Q=0 with a distance between them that equals DJ, because
they intersect Q=0 at the means of the right and left Gaussians.
The default jitter decomposition technique used by SDA2 is Spectral, due to its wide acceptance in the
industry. In general, Spectral decomposition and NQ Scale decomposition will agree well. In the
presense of broad band cross talk (or other broad band bounded, uncorrelated jitter) Spectral can be
fooled into counting that as RJ. NQ Scale is not fooled by that. If Spectral decomp reads much
higher RJ(sp) than NQ Scale's sigma, it probably indicates the presence of broad band bounded
uncorrelated jitter. That is one reason compare NQScale decomposition to Spectral - Rj(nq) should
be close to Rj(sp), if Rj(sp) is higher then the signal was probably affected by cross talk or some form
of broad band, bounded uncorrelated jitter.
Note that both jitter models have "Dual-Dirac" in their names. This is because, once Rj and Dj are
separated, they are combined to yield a Tj number according to the Dual Dirac model, that is TJ = DJ
+ n*RJ, where n is a factor determined by the probability of error specified (see BERPow10, above).
Description
Values
DDSpec
NQS
ShowBitrate Bool
Causes the BitRate (as shown in the ClockRecovery dialog) to be displayed.
Description
ShowDCD Bool
Causes Duty Cycle Distortion to be displayed as a parameter in the SDA Jitter parameter table.
Description
ShowDDj Bool
Causes Data Dependent Jitter (ISI + DCD) to be displayed as a parameter in the SDA Jitter parameter
table.
Description
ShowISI Bool
Causes Inter-Symbol Interference to be displayed as a parameter in the SDA Jitter parameter table.
Description
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