RE: new ibischk3 V3.2.6

Thanks, Todd. :-)

Perhaps I should phrased my request differently to ask for other COMMON
causes including ideal models. I'm not interested in what would happen if
the models used **Superconductors** for traces.....

Aubrey Sparkman
Signal Integrity
Aubrey_Sparkman@Dell.com
(512) 723-3592

> -----Original Message-----
> From: Todd Westerhoff [mailto:twester@hhnetwk.com]
> Sent: Wednesday, January 10, 2001 3:59 PM
> To: Aubrey_Sparkman@exchange.dell.com; khelliwe@acuson.com;
> tony_dunbar@mentorg.com
> Cc: ibis-users@eda.org
> Subject: RE: new ibischk3 V3.2.6
>
>
> I believe that if you connect your circuit to metal plates on
> opposite sides
> of a black hole, you could see such currents.
>
> There are two problems, however:
>
> a) finding conductors that can handle the current, and
> b) keeping the whole thing from getting pulled into the black
> hole in the
> first place
>
> Sorry. Couldn't resist!
>
> Todd ;-)
>
> -----Original Message-----
> From: Aubrey_Sparkman@Dell.com [mailto:Aubrey_Sparkman@Dell.com]
> Sent: Wednesday, January 10, 2001 2:47 PM
> To: khelliwe@acuson.com; tony_dunbar@mentorg.com
> Cc: ibis-users@eda.org
> Subject: RE: new ibischk3 V3.2.6
>
>
> Thank you Tony, I was hoping for a discussion of what the
> IBIS community
> could do about this problem.
>
> And Thank you Kim, for pointing out one of the reasons I
> might receive IBIS
> data with unrealistic currents. Can anyone out there
> describe a realistic
> scenerio (not caused by ideal models) that might cause "giga-amp
> characteristics"?
>
> Thanks!
>
> Aubrey Sparkman
> Signal Integrity
> Aubrey_Sparkman@Dell.com
> (512) 723-3592
>
>
> > -----Original Message-----
> > From: Kim Helliwell [mailto:khelliwe@acuson.com]
> > Sent: Wednesday, January 10, 2001 1:06 PM
> > To: Dunbar, Tony
> > Cc: 'ibis-users@eda.org'
> > Subject: 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
> >
>
>
>