RE: [SI-LIST] : Clamp diodes in models

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From: Abe Riazi (ariazi@anigma.com)
Date: Sun Jan 09 2000 - 23:54:29 PST


>"Ingraham, Andrew" Wrote:
>
>I also have been given simulation models that lacked overshoot clamp
>characteristics. When queried, the IC vendor said that the signals at his
>chip's pins should *never* go even a bit below ground nor above Vdd, so it
>shouldn't matter to our simulations. Right!
>
>Many of us have also seen models with incredibly steep clamp diode curves.
>I don't know which is worse.

A model with missing or weaker clamp curve (as compared to actual
device), can result in simulation waveforms showing greater level of
overshoot than real situation.

On the other hand, a model having steeper clamping ( relative to the
real device) can mask real overshoot or ringing.

Probably, the latter case is more dangerous as it provides a false sense
of security. But, I would like to stress that both of the above types
of model clamping defects can have undesirable drawbacks.

Regards,

Abe
>ariazi@anigma.com

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