Re: Ver. 3.2 and Ver. 2.1 Models

Stephen,

We have done some real system correlation work which we are not
at liberty to share. However, when we do, we perform TDR measurements
of board parameters and use this to calibrate both our field solver
results and in-circuit measurements of driver strength and edge-rate.

We then crank these into our modeling efforts. Our results have been
very good with up to 1.5 Gbit/second data streams.

In most cases, however, we have neither the time, nor the allocated
funds to perform such a rigorous correlation. Instead we make the
assumption that our customers are supplying validated Spice models,
which we use in further extraction and correlation work. In many cases
we work with semiconductor vendors who do correlate their Spice
decks to real silicon. Thus, an IBIS correlation to Spice is quite
valid.

The intent of the accuracy spec is that IBIS models be correlated
to actually measurement. In reality, this is not always possible. We
think that correlation to the Spice is the second best alternative
in most cases.

regards,

scott

Stephen Nolan wrote:

> Thanks, Scott.
>
> More questions:
> It looks like the IBIS Accuracy Handbook simply advises that the user determine
> the transmission-line parameters of the standard test board by doing lab-tests
> (TDR measurements). I'm curious if anyone has done so and would be willing to
> share those numbers. And/or has anyone used a 2D field solver on the board
> design file to get the RLGC parameters for the "50 ohm microstrip transmission
> line which is 8 inches long".
>
> Thanks.
> --
> Regards,
> Stephen M. Nolan
>
> Scott McMorrow wrote:
> >
> > Stephen,
> >
> > Stephen Nolan wrote:
> > >What is "the IBIS Accuracy Trailer"?
> >
> > Here is the directory for it on the IBIS website.
> >
> > http://www.vhdl.org/pub/ibis/accuracy/
> >
> > The Trailer is a bunch of comment lines at the end of
> > a model which are intended to document the correlation
> > of an IBIS model to actual measurements. It was developed
> > by a number of IBIS users, along with the accuracy spec and
> > handbook, because of their frustration with poor model
> > quality.
> >
> > We use the correlation metric which is defined by the
> > specification to compare IBIS simulations with SPICE
> > simulations and document these in the models we produce
> > with the Accuracy Trailer.
> >
> > In our case, the standard test circuit we use is a driver
> > driving a 50 ohm microstrip transmission line which
> > is 8 inches long into a 5pF capacitive load. This gives
> > us loads of information on the quality of IBIS simulations
> > into a fairly complex reflected wave environment. Typically
> > our correlations are within 98 to 99% of the original
> > Spice waveform, according to the metric.
> >
> > We now deliver all models with correlation data to the
> > orignal source. Additionally, we provide reports with
> > pictures of the comparision waveforms to our end customers,
> > which are usually semiconductor manufacturers.
> >
> > best regards,
> >
> > scott
> >
> > Scott McMorrow
> > Principal Engineer
> > SiQual, Signal Quality Engineering
> > 18735 SW Boones Ferry Road
> > Tualatin, OR 97062-3090
> > (503) 885-1231
> > http://www.siqual.com

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com