Subject: RE: [IBIS-Users] Question about warning message
From: Flora, Matthew (matthew_flora@mentorg.com)
Date: Mon Nov 18 2002 - 13:30:47 PST
Dear Fred,
My apologies. I didn't remember the spec saying "must". I thought it said "should". My mistake.
Cheers,
Matthew Flora
> -----Original Message-----
> From: Fred Balistreri [mailto:fred@apsimtech.com]
> Sent: Monday, November 18, 2002 1:09 PM
> To: Flora, Matthew
> Cc: 'ibis-users@eda.org'
> Subject: Re: [IBIS-Users] Question about warning message
>
>
> The reason IBIS models go from -Vcc to 2Vcc is because that is what it
> says in the spec. The following is a direct quote from the spec,
> immediately
> following the section that describes the testing voltage range:
>
> "These voltage ranges must be spanned by the IBIS data. Data derived
> from
> lab measurements may not be able to span these ranges as such
> and so may
> need to be extrapolated to cover the full range. This data must not be
> left for the simulator to provide."
>
> If we don't want people to follow the spec then I would argue that the
> spec needs modification. More importantly because of the spec
> ibis tools
> all
> conform to the voltage testing as prescribed, included s2ibis which a
> lot
> of people use. So I don't think the statement about people blindly
> following
> the voltage requirement is true. It may be more of the case that
> historically
> this is what we have done, which can be traced back to where it all
> started,
> the specification itself.
>
> Best Regards,
>
> "Flora, Matthew" wrote:
> >
> > Hi All,
> >
> > The non-monotonic warnings are generated by the IBIS Golden
> Parser because it is
> > not summing the I-V table together before checking for
> monotonicity. I believe
> > there is a pending bug (71) fix to the IBIS Golden Parser
> which will sum the
> > tables before the monotonicity check.
> > http://www.vhdl.org/pub/ibis/bugs/ibischk/bug71
> >
> > It has been argued that the extreme currents are acceptable
> because a part
> > pushed to those extremes may actually give extreme current
> in the instant before
> > it melts. I believe this is because people are blindly
> following the -VCC to
> > 2VCC voltage range recommendation for I-V tables and so are
> trying to come up
> > with currents well outside of the normal operating region
> for some parts. I
> > don't know if the IBIS spec actually say it, but I believe
> the intention is that
> > the I-V tables should include all of the voltages where
> "interesting" things
> > happen. If the part was never designed to handle voltages
> out at -VCC or 2VCC,
> > then the tables need not include such voltages. I believe
> this was more common
> > when more people were doing bench measurements to make the
> tables and they
> > limited the voltage range to actual voltages that got close
> to melt down, but
> > not beyond.
> >
> > Just my two pence,
> > Matthew Flora
>
> --
> Fred Balistreri
> fred@apsimtech.com
>
> http://www.apsimtech.com
>
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