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Chapter 4 Demo Waveforms
Demo 2: Data-to-Clock
Notice that the break-away in the late side window margin data (due to
the errant pulses in the histogram) is causing a poor curve fit for the late
portion of the plot. (The dashed line is the extrapolation). While the
margin extrapolation algorithm assumes that the distribution is purely
Gaussian, this is a case where it is clearly not. You may therefore wish to
experiment with fitting or weighting the extrapolation more towards the
"tails" of the distribution rather than the center of the distribution.
Conversely, you may wish to ignore certain outliers which may be due to
media defects, or other known abnormalities. The HP E1741A allows you
to modify the data range over which the extrapolation is fitted, as shown
next.
3
Click on the right marker, and while holding the left mouse button down,
drag the marker on the late portion of the window margin curve to where
the data portion of the curve starts to break away; about −3.5 (look at the
y-axis, right marker readout at the bottom of the display).
By modifying the default extrapolation values, you will be able to cause
the extrapolation to ignore this break-away in the curve.
4
Select Window Margin>Extrapolation levels.
5
Highlight the "−10" value for the extrapolation.
6
Enter "−3.5" and click the OK button.
This directs the software to use only error-rate data in the range of
−1.5
−3.5
10
to 10
when generating the extrapolation curve.
Getting Started Guide
4-21
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