RE: new ibischk3 V3.2.6

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
>

 
Received on Wed Jan 10 09:59:44 2001