Subject: Re: accuracy BIRD

From: [email-masked]
Date: Mon, 15 Mar 1999 12:24:50 -0600

Stephen,

Thanks for the insight.  This clears up my question, and I believe Syed's,
too.  Actually, I went back and re-read section 3.2.2 of the Cookbook, and
you said it quite well there.  The simulator NEEDS the no-load VT tables to
generate a realistic stimulus, if you will.  The VT tables with a complex
load are icing on the cake and useful for verifying simulator results.

What the Accuracy Subcommittee is proposing is some new complex loads that
involve transmission lines.  (And we'll probably come up with more when we
start looking at more advanced drivers.)  We can use these extra loads to
validate both lab results AND simulator results against the "golden
waveforms" in the IBIS datasheet - a cool thing.  The real question is,
should we add some new keywords and/or subparameters to describe these new
loads, thereby facilitating automated simulation and correlation, or should
we count on comments to describe the load.  I like the automated approach
myself, but I agree with Bob Ross:  let's not make the IBIS Accuracy Spec
dependent on which of the two approaches we choose to use.  That way we can
proceed with getting it approved.

Thank you all for your input.

Greg Edlund
Advisory Engineer, Critical Net Analysis
IBM
3650 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
[email-masked]

---------------------- Forwarded by Gregory R Edlund/Rochester/IBM on
03/15/99 12:06 PM ---------------------------

Stephen Peters <[email-masked]> on 03/15/99 11:54:07 AM

To:   Syed Huq <[email-masked]>
cc:   [email-masked], Gregory R Edlund/Rochester/IBM
Subject:  Re: accuracy BIRD

Hello Syed, Greg:

  Sorry for the delayed response -- I was out of the office back week and
am just now getting back to my mail.  To elaborate:  I was trying to make
a distinction between at V/T table that is created by an output driving a
pure, non-reactive impedance, and a V/T table created with the output
driving
a more complex load.  The *former* V/T table contains the data the
simulator
needs/uses when building the output model.  Specifically, it describes how
the pullup and pulldown transistor turn on/off, and does not -- indeed,
should
not -- contain any extra time constants due to reactive elements.   In the
latter case (complex, reactive impedences) the inclusion of these waveforms
is a check.  Given the model that was build with the first V/T tables, the
question is can the simulator produce the waveform of the second case.

Hope this helps clarify things.

 Regards,
 Stephen Peters
 Intel Corp.

> Hi,
>
> Since the V/T tables allow keywords such as C_dut, R_dut, L_dut, doesn't
> that imply that it DOES use the package numbers. I am a bit confused
about
> Stephen's statement below regarding old VT tables..
>
> Syed.
> Cisco Systems, Inc
>
> >
> > On the question of "golden waveforms" vs. "regular old VT tables,"
Stephen
> > Peters mentioned that there is a difference between the two.  Golden
> > waveforms have the package while regular old VT tables do not.  Is
there
> > any syntactical construct within IBIS to differentiate between the two?
> > Care to embellish here, Stephen?
> >
> > Thanks all.
> >
> > Greg
> >
> >
> >

---

From: Fred Balistreri <[email-masked]>
Date: Mon, 15 Mar 1999 12:35:49 -0800

> > > Care to embellish here, Stephen?
Actually there is always a load on the IBIS models I have seen. The load
is typically 50 ohms to gnd or vcc. Because of this the simulation 
vendors must extrapolate the no load answer. The DC loads are presumably
put there to determine turn off and turn on currents. One other comment.
The load is always a complex impedance. This is because c_comp is
required. 

Best Regards,

-- 
Fred Balistreri
[email-masked]

http://www.apsimtech.com