FreeLists / si-list / [SI-LIST] Re: Spice

[Ivor Bowden <ivor@xxxxxxxxxxx>]

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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