Subject: RE: [IBIS-Users] number of waveforms
From: Lynne Green (lgreen@cadence.com)
Date: Wed May 28 2003 - 10:55:00 PDT
Hi, Erik,
The Vref values should be the MIN and MAX signal swing range (Vcc and 0
for CMOS). Rref should be the standard load (50 Ohms for PECL).
The 4 tables (2 rising, 2 falling) are sufficient to define the
(time-dependent) fitting coefficients that are commonly used to
characterize transitions.
Different simulators might do different things with additional tables.
SPECCTRAQuest uses all available tables.
Best regards,
Lynne
-----Original Message-----
From: erik.van.der.ven@philips.com [mailto:erik.van.der.ven@philips.com]
Sent: Wednesday, May 28, 2003 1:15 AM
To: Lynne Green; ibis-users@eda.org
Subject: RE: [IBIS-Users] number of waveforms
Dear Lynne,
Thank you for your reply.
I am trying to model a PECL output buffer.
So the output is normally terminated with 50 Ohm to Vcc-2V.
I am wondering how accurate the simulations are with an IBIS simulator
if the load differs from the reference load.
Will the accuracy incease if I add a second waveform set with different
load, or to another termination voltage?
Will the simulator produce a more acurate behavior model if I provide a
second waveform set, or does it use the waveform table that is most
close to the load to be simulated?
With kind regards,
Ir. Erik van der Ven
Room DB1032
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
"Lynne Green" <lgreen@cadence.com>
05/27/03 06:33 PM
To: Erik van der Ven/NYM/SC/PHILIPS@EMEA2
cc:
Subject: RE: [IBIS-Users] number of waveforms
Classification:
Hi, Erik-
The typical recommendation is 4 waveforms tables at the same load
(rising to Vcc, rising to GND, falling to Vcc, falling to GND). That
captures how the pullup and pulldown transistors turn on and off, so
tables at additional loads are not needed.
Additional waveform tables are permitted (up to 100 according to the
IBIS spec). But the more tables you use, the slower a simulator will
run.
- Lynne
-----Original Message-----
From: erik.van.der.ven@philips.com [mailto:erik.van.der.ven@philips.com]
Sent: Tuesday, May 27, 2003 6:43 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] number of waveforms
Dear IBIS users,
It is possible to specify more than one waveform table, for instance
with different loads.
I have studied many IBIS models by semiconductor companies. All models I
have seen give only one waveform (both rising and falling).
What is the purpose of specifying more than one waveform? Does this
yield better results in the simulator if the load differs from the
standard load?
With kind regards,
Ir. Erik van der Ven
Room DB1032
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
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