RE: [SI-LIST] : High Speed Design by Rules of Thumb vs. Simulation

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From: Abe Riazi (ariazi@anigma.com)
Date: Mon Feb 21 2000 - 11:03:07 PST


Scott:

Thank you for a very informative response.

I have inserted below comments regarding simulation efficiency, critical
length and scaling.

>>
>> By what means can efficiency of a SI simulation be optimized?
>>

>I'm not so sure what you mean here. If you mean analysis performance in
terms
>of accuracy and time to completion, then this is almost a non-issue these
days.

By efficiency I meant speed and accuracy, and believe that towards its
optimization it is important to develop a comprehensive model library,
simulation plan and script programs.

  A SI simulation can be at times slowed down due to requirement for
obtaining the necessary models and validating them. Model library
development should be aimed at minimizing such loss of time, without
sacrificing accuracy.

  Simulation plan should be designed to guide the simulation from start
to finish in a most time and cost efficient fashion.

  In a simulation there are often time consuming manual steps which can
be eliminated by means scripts.

>Critical length is not an issue. The only issue is desired accuracy, as is
the case
>in all engineering endeavours. Length is an artifact of what is truly
desired,
>a particular accuracy in terms of simulated voltages and times. Determine
>what is reasonable accuracy for a typical design and the tools, methods and
>simulation variables fall into place.

Critical length which has been previously discussed in this forum,
provides a valuable yard stick for distinguishing the lumped and
distributed circuit elements, and hence when transmission line effects
begin to occur. The rule that simulation is indicated when trace/stub
lengths exceed Lc is useful, although there are exception as noted in an
earlier post.

>Scaling ... hmmm ... I'm not sure how this applies. What would one scale?
>Simulators certainly scale fairly well in terms of performance.

To my knowledge, "scaling" is frequently used by microwave engineers and
scientists particularly in areas related to antenna theory. Perhaps,
frequency scaling is not so well known in the field of signal integrity,
but there is an article on this subject written by Dr. Howard Johnson
entitled "How Fast is Fast" available on his web site .

Regards

Abe
ariazi@anigma.com
ARIAZI@prodigy.net

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