HP E1725C, Getting Started Manual

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Chapter 4 Demo Waveforms
Demo 2: Data-to-Clock
4-20 Getting Started Guide
4
These are the corresponding window margin results for the data-to-clock
histogram. Due to the incorrect delay from trigger value, the histogram
(shown above the window margin) has a number of measured intervals
that are set apart from the main distribution. You can see these on the left
side of the histogram on the panorama display.
So why does the right side of the window margin show poor performance
while the outliers are on the left side of the histogram? What happens
when deriving window margin data from data-to-clock histogram
intervals, is that the margin plot is reversed, with respect to the segment
center from the histogram. This reversal allows the margin data to
correctly indicate how the data is varying with respect to the segment
center. Of course, with a data-to-clock measurement, both data and clock
variations contribute to the end result. This reversal is why the late side
of the window margin graph shows poor performance, a consequence of
the “errant measurements” on the early side. Note that the extrapolated
late margin is
−
10.32%, indicating that the 10E
−
10 error rate on the late
side is beyond the decode window boundary.