Re: new ibischk3 V3.2.6

I have another perspective. This problem is almost certainly caused
by diode models in the SPICE netlist that are "ideal" models; that
is, there is no series parasitic resistance (RS) specified.

And I think it's more than reasonable for the IBIS community to demand
that suppliers of SPICE or IBIS models do not use such ideal components
in the model. This is a well-known SPICE trouble spot, and anyone who
still perpetrates that sin appears to me to be a rank amateur. It causes
me to wonder what other inaccuracies exist in the models that exhibit this
problem.

Kim

"Dunbar, Tony" wrote:
>
> Aubrey,
>
> First of all, let me just set the scene. In this e-mail, I am ONLY referring
> to the situation of gross currents in the V-I tables.
>
> >From a purist stand-point, I agree with you. Unfortunately, in my experience
> the reality is that many, many IBIS models derived from SPICE exhibit these
> giga-amp characteristics. I think what Bob means is that the model is
> correct in that it reflects what the SPICE model has. A further reality is
> that the IBIS forum is not going to change the world; these decks and models
> are not going to change to satisfy this anomoly. Fortunately, they usually
> occur well away from the normal operating region and normal clamping region
> so, in actual operation, they don't give us a problem.
>
> Given that this is reality and it's not going to change, I think we (the
> IBIS forum) need to look at what, if anything, we are going to change to
> deal with it? Maybe we need to change things a little to be closer to this
> normal operation. One question is, 'what is the reasoning behind the
> (somewhat large) range of (2xVCC to -1xVCC) for the V-I tables?'; can this
> be truncated? Or, better (IMHO), check that the clamp currents are
> reasonable(?) within a tighter range; i.e. closer to the normal operating
> region and to a limit more aligned with an expected clamping event; e.g.
> VCC+1.0V and GND-1.0V.
>
> Yes, it sounds like capitulation, but I think it's the only practical
> course.
>
> -----Original Message-----
> From: Aubrey_Sparkman@Dell.com [mailto:Aubrey_Sparkman@Dell.com]
> Sent: Wednesday, January 10, 2001 11:01 AM
> To: bob_ross@mentorg.com; shuq@cisco.com
> Cc: ibis-users@eda.org
> Subject: RE: new ibischk3 V3.2.6
>
> Bob,
> I'm not sure I agree with your statement that a model with end point I-V
> currents that are "extremely large (such as 1e20)" "might actually be
> correct" even if those data points are produced from a valid spice deck.
> The purpose of a model is to reflect reality where possible and 1e20
> amps????
>
> Aubrey Sparkman
> Signal Integrity
> Aubrey_Sparkman@Dell.com
> (512) 723-3592
>
> > -----Original Message-----
> > From: Bob Ross [mailto:bob_ross@mentorg.com]
> > Sent: Tuesday, January 09, 2001 7:26 PM
> > To: Syed Huq
> > Cc: ibis-users@eda.org
> > Subject: Re: new ibischk3 V3.2.6
> >
> >
> > Syed:
> >
> > The new ibischk3 changed the Warning message to an Error
> > message when the mismatch exceeded 10%. In your example,
> > the mismatch between 0.41 and -0.71 exceeds the 10% value
> > of the range (.21v). There may exist a real problem that
> > needs to be examined. This change is documented as BUG47:
> >
> > http://www.eda.org/pub/ibis/bugs/ibischk/bug47
> >
> > However, the -0.71 value is suspicious. I have seen a
> > similar problem when some of the end point I-V currents are
> > extremely large (such as 1e20) and cause ibischk3 to
> > not properly converge to the correct DC endpoints. You
> > might check this and try smaller values if such large
> > values exist. Your model might actually be correct.
> >
> > Bob Ross
> > Mentor Graphics
> >
> >
> > Syed Huq wrote:
> > >
> > > I ran a model with the NEW ibischk3 ver3.2.6 and get this:
> > >
> > > new version:
> > > ERROR - Model XYZ_IO: The [Rising Waveform]
> > > with [R_fixture]=50 Ohms and [V_fixture]=2.5V
> > > has TYP column DC endpoints of 0.41V and 2.50v, but
> > > an equivalent load applied to the model's I-V tables yields
> > > different voltages (-0.70V and 2.50V),
> > >
> > > In the earlier version(V3.2.5),this would show up as a
> > WARNING. Since now
> > > it shows up as ERROR, the file fails.
> > >
> > > old version:
> > > WARNING - Model 'XYZ_IO': TYP AC Rising Endpoints ( 0.41V,
> > 2.50V) not within
> > > 0.042V (2%) of (-0.70V, 2.50V) on VI curves for
> > 50 Ohms to 2.5V
> > >
> > > Why was this changed to ERROR ?
> > >
> > > Syed
> >

-- 
Kim Helliwell
Senior CAE Engineer
Acuson Corporation
Phone: 650 694 5030  FAX: 650 943 7260