[SI-LIST] : limitations of spice for SI modelling

Christopher Albert (Christopher_Albert@notes.teradyne.com)
Tue, 9 Mar 1999 11:51:47 -0500

The pspice manual claims that the maximum fft size is 8192 points regardless of
the simulation parameters. This seems to imply a limit on time resolution
relative to length for lossy transmission lines. For example, a transmission
line that is 10nS long, neglecting loss would require an impulse response
somewhat longer than this. 8192 time points/10nS suggests a time resolution of
>1 ps. In practice, I believe that the problem is worse because the number of
points may be less than 8192 and the impulse response computed may be much
longer than necessary. Even so, it is probably a small source or error, but it
is disturbing because it seems to be independent of reltol and may grow fairly
large depending on the .tran parameters that are chosen.

Have I missed something in my analysis ? Does anyone have firsthand experience
with this ?

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