Re: Drive-on-demand

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
 
Received on Thu Sep 7 11:08:00 2000