Re: accuracy BIRD

Greg,

Golden Waveforms are a great idea!

>1) Is it necessary to describe the test loads in a machine-readable
>fashion, similar to the distributed package model and EBD options already
>present in IBIS? Or should we opt for the more simple approach of adding a
>waveform with comments describing the test load?

A "machine readable" format is prefered in order to facilitate automated
validation.

You mention using SPICE as the waveform creator so are transmission lines
and package info really needed?

If you're going to standardize the golden waveform loads, I suggest:

  1) No Transmission lines (we're not testing the accuracy of T-Line
modeling or
     T-line extraction parameters are we?).

  2) No package parasitics (or they are spelled out explicity within the
waveform).

  3) A Shunt R to the Positive Rail, the Negative Rail and halfway in
between. R should be
     near the impedence of the Transmission line the driver expects to see.

  4) A Shunt C=50pF may prove informative also.

>2) How does one distinguish between a golden waveform (w/ package) and a
>regular old VT table (w/o package) in IBIS?

I claim that a regular old VT table **IS** a golden waveform.

It doesn't seem appropriate to place waveforms that use a particular package
"within the [Model] block" using IBIS since a particular [Model] block may
be used in with different packages. The [Model] block is meant to represent
the output stage w/o (independent of) the package parasitics.

If waveforms with particular package parameters are generated then they
would have to be spelled out in some parseable format at the location of the
waveform. Otherwise, there is the danger that someone will edit the package
information at the top of the .ibs file and not re-generate the waveforms.

Regards,

Chris Rokusek
Viewlogic Systems
Received on Thu Mar 11 18:49:14 1999