Re: [SI-LIST] : Does IBIS describe output transition which both MOS turned on?

Chris Rokusek (crokusek@viewlogic.com)
Wed, 13 May 1998 20:39:35 -0700

Okay, can't resist here's my two cents...

Fred Balistreri wrote:
> Id is not crowbar. So you still have to go back to the I/V data and dig
> it out as I already mentioned. V/t curves were originally intended to
> model the ac or switching characteristics which IBIS was (is?) lacking.
> Sure the information is there so is ground bounce to some degree.
> Remember the 4 v/t curve information only got added recently, but the
> single v/t curve has been in IBIS for quite some time. Chances are the
> users haven't seen a 4 v/t model yet.

Since IBIS V2.1 (circa 1995) there has been a limit of 100 waveform
tables per model allowing many "arbitrary" loading conditions. One of
the reasons multiple waveforms were allowed right from the start was to
support a mechanism for estimating VCC, GND & the dreaded Crowbar
currents.

I've seen many 4 v/t models for quite a while but I also still see many
1 v/t models or multiple X v/t waveforms to useless loads.

***
*** MODEL BUILDERS PLEASE READ ON...
***

More recently an IBIS model building cookbook that details recommended
loading conditions was posted for public download:

http://www.eia.org/eig/ibis/tools.htm

Click "IBIS Cookbook for V2.1 (Oct 13th '97)"

Best Regards,

Chris Rokusek
Viewlogic Systems