[SI-LIST] Re: Spice
- From: Ivor Bowden <ivor@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 04 Feb 2005 10:17:10 -0800
Hi Si Experts,
Yesterday I posted a request for Spice help. I would like to thank all
those who replied, some multiple times, with information and ideas.
The problem I was having was I was trying to simulate a pulse driven
down a cable. I used a lossless transmission line with matching
terminations on each end. My output waveform was not as expected, there
was over/under shoot and excessive rise / fall time. I was using the
SIMetrix Intro v5.0f program ( http://www.catena.uk.com/index.html ).
My first error was in specifying a input voltage with 0 rise time:
V1 V1_P 0 PWL 0 0 500n 0 500n 1 1.5u 1 1.5u 0
this was causing the over/under shoots.
The second problem of excessive rise/fall times was due to a too large
maximum step:
.TRAN 100p 2u (defaulted to 40n)
I find that specifying a smaller maximum step results in smaller
risetimes, for example with a 1nS input rise time a 100pS TMAX resulted
in identical input & output waveforms.
Once again, Thanks!
Ivor
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