IBIS - EIA IBIS Open Forum Activity: RE: [IBIS] Subtracting &quo

From: lgreen <lgreen22@mindspring.com>
Date: Wed Dec 22 2004 - 16:27:55 PST

Hello, David,

The intent is to have V-t table data that matches the actual delay of the
buffer under the specified load for the V-t table. In most cases, the delay
from the start of the SPICE output to the time when the toggle signal
reaches the buffer is the same for all tables. However, there is an
exception to the "subtract equal times" when the rising and falling tables
are generated using the same SPICE simulation.

One example: rising tables starting at 0.0nsec and falling tables starting
at 50.0nsec. In this case, 50.0nsec was subtracted from only the falling
table.

Happy Holidays!

- Lynne

"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@mindspring.com

-----Original Message-----
From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Tom
Dagostino
Sent: Wednesday, December 22, 2004 10:21 AM
To: David Mahashin; ibis@eda.org
Subject: RE: [IBIS] Subtracting "Lead-in" Offset from V-t curves

You have to strip the same amount of time from all waveforms. The purpose
of the multiple VT waveforms is to show how one device turns on and the
other device turns off. If you start moving the waveforms around then you
could have situations where both the pullup and pulldown device are on at
the same time or neither device is on during the transition. Some
simulators flag this kind of condition and generate errors for the model.
The IBIS parser does not check for this conditions

Tom Dagostino
Teraspeed Consulting Group LLC
503-430-1065
tom@teraspeed.com
www.teraspeed.com

-----Original Message-----
From: owner-ibis@eda.org [mailto:owner-ibis@eda.org]On Behalf Of David
Mahashin
Sent: Wednesday, December 22, 2004 9:36 AM
To: ibis@eda.org
Subject: [IBIS] Subtracting "Lead-in" Offset from V-t curves

Hi,

I have a question concerning the offset on V-t curves. I realize that most
simulators (e.g. Hyperlynx) have the option of automatically stripping the
"lead-in" offset.

However, if I do want to subtract the offset manually, is it necessary to
subtract the same offset amount to all of the rising/falling waveform
tables?

What is the effect of subtracting different offset amounts such that all the
waveforms rise/fall at the same point in time? Will this incorrectly model
the input to output delay of the buffer?

Thanks,

David

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