Re: Drive-on-demand

Hi Bob, Frabrizio,

I don't see what the problem is.
Shouldn't multiple VT tables provide
enough data to modeling this softening effect?

Kellee

At 11:05 AM 9/7/00 -0700, Bob Ross wrote:
>Fabrizio:
>
>Initially I thought that the [Submodel] Bus_hold could be
>configured to create the model. However, what is needed
>is a trigger that turns off a submodel driver, rather than
>turns it on.
>
>DC suggested creating a "negative" impedance driver to
>accomplish the same effect. The driver would be
>switched in, and the negative impedance in parallel
>with the existing driver impedance would create the
>effect of a higher impedance driver. I cannot think
>of a good way to do this without causing some other
>bad interactions.
>
>Bob Ross
>Mentor Graphics
>
>
>"zanella, fabrizio" wrote:
> >
> > Bob, DC, are you referring to the double drive devices like AVC logic,
> which
> > has fast drive in the 20-80% region and then softens the drive at the
> > corners? This is a technology we've wanted to evaluate for some time, but
> > the IBIS standard does not support it yet.
> > Regards,
> > Fabrizio Zanella
> > EMC corporation
> > fzanella@emc.com
> >
> > -----Original Message-----
> > From: Bob Ross [mailto:bob_ross@mentorg.com]
> > Sent: Thursday, August 31, 2000 9:24 PM
> > To: ibis@lumbercartel.com
> > Cc: ibis-users@eda.org
> > Subject: Re: Drive-on-demand
> >
> > D.C.:
> >
> > Based on your description, I do not believe Bus_hold will work
> > directly. I do not believe simulators will work with
> > "negative" currents in the tables - meaning doing the
> > opposite of what is expected or creating a negative
> > impedance buffer that acts opposite of a conventional buffer.
> >
> > Opposite polarity I-V tables will probably be flagged
> > as an error by the ibischk3 parser. Therefore it would
> > not be legal.
> >
> > I cannot think of any clever alternative with IBIS
> > Version 3.2.
> >
> > However, I believe the new macro language under discussion by
> > the IBIS Futures Working Group will be able to handle this
> > situation (this would be a good test case).
> >
> > Bob Ross
> > Mentor Graphics
> >
> > "D.C. Sessions" wrote:
> > >
> > > Need to double-check this. It seems that there are standard
> > > logic components which, on output, sense the output voltage
> > > and adjust drive current in response.
> > >
> > > No, I don't mean bus hold. These parts drive LOW hard when
> > > the output voltage is above a certain threshold and cut the
> > > drive when the output is below that threshold. Rising-edge
> > > drive is similar.
> > >
> > > Yes, I know that this is of dubious stability. Nobody asked
> > > me if they should do it this way, but the manufacturers want
> > > to make this a JEDEC standard and I'm trying to help them
> > > put together an IBIS model. Which, as far as I can tell, is
> > > possible using
> > >
> > > Submodel_type Bus_hold
> > >
> > > and having negative currents in the [Pulldown] and [Pullup]
> > > tables.
> > >
> > > 1) Have I missed a better way to do this?
> > > 2) Will this be legal?
> > > 3) Will this break EDA tools?
> > >
> > > --
> > > D. C. Sessions
> > > ibis@lumbercartel.com

---------------------------------------------------------
Have a great day....
Kellee Crisafulli
Innovative tools for SI,EMC,X-talk and IBIS tools
E-mail: <mailto:kellee@hyperlynx.com>
web: <http://www.hyperlynx.com>
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Received on Thu Sep 7 11:47:50 2000