LeCroy DDA 7 Zi series, Operator'S Manual

Page: 408 / 544

WavePro 7Zi
407
WP700Zi-OM-E-RevA
TIE Histogram
A TIE histogram is often useful to display the raw measured histogram of the measured jitter values because it
can give clues as to the sources of deterministic jitter and it also gives a good indication of whether the
extrapolated total jitter value is likely to be accurate. The bins in the histogram at the extreme tails (the last 5 to 10
bins on each side) are used to determine the best-fit curve (see the Theory section for more details). Generally, if
the histogram is smooth between the two tails, that is, there are no deep troughs in the shape, the curve fitting
and extrapolation will give an accurate and stable Tj value.
There are some cases where very large amounts of ISI or periodic jitter cause deep troughs in the shape of the
histogram. In these cases, a very large population is required in the histogram to ensure a sufficient population in
the tail regions to achieve a reliable fit. Generally 1.5 to 2 million measurements in the histogram are sufficient to
resolve the tails, but more data is always helpful. A histogram that appears smooth is a good indicator that the
total jitter will be accurate.
The TIE histogram shows the measured jitter distribution that is the source for the bathtub curve and total jitter
parameter.
1. Touch the Jitter Histogram button. The histogram will be displayed in the center of the bathtub curve.
2. Touch the Bathtub button to toggle the histogram display off.
DDJ (Synchronous N-Cycle Plot)
The DDj (data dependent jitter) is measured on the data stream when the Conventional jitter breakdown method
is selected. The DDj is measured by finding the average crossing time for each edge in the data pattern and
comparing this to the nominal crossing time, based on the expected bit rate of the signal under test. This
measurement requires a repeating data pattern to operate. If the data pattern in the signal does not repeat at
least once in the acquired data record, the DDj parameter will indicate zero even though this type of jitter is
present. A graphical display of the DDj can be viewed by clicking the
ISI button in the Jitter menu. This display
shows the position error of the average crossing point for each edge in the pattern.