RE: [IBIS] Question regarding V-t tables

Arpad,

I may be reading more into your statements than exist
but, it looks to me like the drivers are not identical
in some way. If they were identical the waveforms
should correlate. In the case you describe it seems
that it would be necessary to create separate models
for the P and N to obtain the necessary correlation.

David Lieby, Siemens Medical

--- "Muranyi, Arpad" <arpad.muranyi@intel.com> wrote:

> Thanks Chris, Bob, and Andy for your responses. Let
> me give a simple
> example for the reason I was asking this.
>
> I made an IBIS model for a differential buffer. Two
> V-t curves were
> generated for it, one rising and one falling
> waveform. One of them
> was saved from the non-inverting pad, and the other
> from the inverting
> pad. The input was stimulated with only one edge.
> The IBIS model
> correlates very well on every other transition, but
> not so well on
> the rest of the transitions, see:
>
>
http://www.eda.org/pub/ibis/summits/oct03/muranyi.pdf
> on page 34.
>
> I didn't verify this yet, but I suspect that if I
> would have generated
> two more waveform tables with a stimulus going the
> opposite way and used
> those waveforms for the transitions that don't match
> so well, I would
> have gotten all transitions match well.
>
> In this particular case I could probably do it with
> regular IBIS
> syntax if I made two ***different*** [Model]s with
> the two sets of
> waveforms
> (one for the "P" pad and the other for the "N" pad)
> and associated them
> with the normal [Diff Pin] keyword.
>
> However, there may be other, more complex situations
> when this may not
> be possible. In those cases I cold envision a *-AMS
> solution which
> still
> uses regular IBIS data, but adds a waveform selector
> logic that is based
> on a set of logic equations which can detect data
> patterns and select
> the
> corresponding V-t tables on the fly for a given
> transition or pattern
> from
> the otherwise normal IBIS [Model].
>
> This was the reason for my question. How could I
> put multiple waveform
> tables in a [Model] with the same Rfixture and
> Vfixture parameters, and
> tell the simulation engine which one to use
> depending on the input
> stimulus (rise or fall), or depending on the data
> pattern on the input
> (0101010, or 00001111, etc)? Please note that the
> I-V and V-t curve
> processing algorithm would be the same as before
> otherwise, i.e. basic
> IBIS algorithms would still work. This is just like
> a [Model Selector]
> like Bob suggested, except that it does it on the
> fly, and could be
> controlled by more complicated data pattern
> definitions.
>
> I know, this could be done completely in *-AMS
> without touching the
> legacy portions of the IBIS spec, so I am not
> pushing for this too hard.
> I just wanted to gather some opinions to see if it
> would be worth
> writing
> a BIRD on this, or forget it and do it strictly in
> *-AMS.
>
> Any (new) feedback would be appreciated.
>
> Thanks,
>
> Arpad
>

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Received on Thu Sep 9 08:31:33 2004