[SI-LIST] : Re: eye patterns

Mike Jenkins (jenkins@lsil.com)
Tue, 12 May 1998 14:34:04 -0700

Craig,

To view eye diagrams in SPICE, you can create a parameter that is
a "sawtooth" waveform with a period that is a multiple if the unit
interval ("UI"). For example:

.probe cyc=par('n*UI*((time/(n*UI)+Phase)-int(time/(n*UI)+Phase))')

Selecting cyc as the x-axis parameter in the plot displays the
y-axis data waveform as an eye diagram. Different values of "Phase"
between zero and one will time-shift the data eye. Using n=1 gives
a single eye, n=2 shows two eyes, etc..

The only other thing to look out for is to blank out the "flyback"
part of the sawtooth. That is, the waveform plots from left to
right, then wants to retrace to the left side. If you dont blank
this retrace, lots of straight lines cross your beautiful eye
diagram. In HSPICE's HSPLOT, setting the "m" setup parameter to
YES does this blanking. There's also a way in MWAVES, but I don't
recall the syntax.

Good luck,
Mike

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