Subject: Re: Avoiding Double Counting

From: Jon Powell <[email-masked]>
Date: Thu, 21 Nov 1996 08:58:20 -0800

I you do not specify the appropriate VI curves for the clamps then the
device cannot be tri-stated in the simulation.

There are also devices that drive the clamps to different rails (3v
devices do this at times).

There is also the possibility of the high or low clamp being driven when
the device is in the opposite state (low or high). Though unusual, it
could happen.

If none of these things are a concern then you can combine the clamps.

ps: At Quad design, we do not explicitly combine the curves unless the
data is non-monotonic. We do not believe that this is always appropriate
and that is why I was always against the non-monotonic data in the
un-combined waveforms. (though I "gracefully" bowed to public opinion).

Jon

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From: Kellee Crisafulli <[email-masked]>
Date: Thu, 21 Nov 1996 11:35:45 -0800

At 05:30 PM 11/20/96 PST, you wrote:
>
>It seems that we go thru too much data crunching and Simulators
>simply connect the two tables anyway.
>
>Possible I am missing something very important here. Pls comment.
>

If as a model developer you can separate the diode characteristics from
the output characteristics than you should create two separate tables.
If you cannot separate them than only a single table is needed.  The reason
there are two tables is so the simulators can treat the clamp diodes more
accurately and have data on the clamp diode.

So... it may be that your method of creating IBIS models does not allow you
to separate the clamp diode from the output buffer and that is ok.  The
simulators can do a slightly better job modeling if clamp diode information
is separate and truly represents the clamp diode.

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Have a great day...Kellee Crisafulli, HyperLynx Inc.
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