IBIS-USERS - EIA IBIS Open Forum Users Activity: RE: [IBIS-Users

From: Tom Dagostino <tom@teraspeed.com>
Date: Tue Oct 12 2004 - 21:02:54 PDT

Well, not really true.

Say for instance you have a buffer that has a 1 nsec rise and fall and the
delay in the buffer is 20 nsec before the edge occurs (I've seen worse in
real models). Now lets try to make this toggle. Apply a 100 MHz input
frequency to the buffer. It will try to make a positive transition. But it
will have to wait 20 nsec before this can happen. But at 10 nsec the input
has decided that now it wants to go negative. In this example the buffer
will never toggle.

In a properly constructed output model the delay is minimal and the delay is
proper for both the rising and falling waveforms. The min, typ and max VT
curves will likely have different delays with the max the least amount of
delay.

Many simulators now have features that will strip out common delay in the
rising and falling VT curves but this may have the affect of removing any
asymmetry the buffer may impose on a 50% duty cycle stimulus.

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

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Aubrey_Sparkman@dell.com
Sent: Tuesday, October 12, 2004 6:54 PM
To: nitin.bhagwath@hp.com; rlecona@siu.buap.mx; ibis-info@eda.org;
ibis-users@eda.org
Subject: RE: [IBIS-Users] V-t curves offset

Nitin,
I think you are correct; the delay of an IBIS buffer isn't relevant.

Ramiro,
If you are testing the IBIS buffer in HSPICE, try adjusting the delay of
the input stimulus to get the output waveforms aligned.

Aubrey Sparkman
Enterprise Engineering Signal Integrity Team
Dell, Inc.
Aubrey_Sparkman@Dell.com
(512) 723-3592

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Bhagwath, Nitin
Sent: Tuesday, October 12, 2004 8:22 PM
To: RODRIGUEZ_LECONA_RAMIRO; ibis-info@eda.org; ibis-users@eda.org
Subject: RE: [IBIS-Users] V-t curves offset

Hi Ramiro,

Ibis models are one port models, and so do not have a concept of
input-to-output delays. So you can't really compare a transition time
from a two port Spice model with a one port Ibis model which might use a
stimulus to generate its output waveform.

If this has changed, or is being planned to change, I would be most
interested in finding out (and using!).

Regards
-Nitin

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of RODRIGUEZ_LECONA_RAMIRO
Sent: Tuesday, October 12, 2004 5:36 PM
To: ibis-info@eda.org; ibis-users@eda.org
Subject: [IBIS-Users] V-t curves offset

Hi all,

I'm working with IBIS models validation and I have a problem
correlating the IBIS model with transistor level buffer in HSPICE. I
simulate both buffers with the same conditions (same load, temperature,
voltage supply) and the rising/falling edges of the outputs are equal
but there is a delay between IBIS model output waveform and transistor
level

buffer output waveform. I shift the V-t Tables in the IBIS model to
compensate the delay and the output waveforms are matched but this
occurs when the input signal has rising/falling times equal to the
rising/falling times used to extract the IBIS model, if I use a input
signal with rising/falling times lower than the rising/falling times
used to extract the V-t curves then the buffer implemented with the IBIS
model has again a delay.
   What happens?
   How can I understand this? How can I avoid this delay?
   Or this phenomenom is normal because the important thing is the edge
waveform (buffer switching behavior) and the delay obtained is not
relevant?
   Or the V-t curves obtained with specyfic rise/fall times are only
valid to simulate buffers with input signals with the same rise/fall
times ?

Thanks.

Regards.

|------------------------------------------------------------------
|For help or to subscribe/unsubscribe, email majordomo@eda.org with just

|the appropriate command message(s) in the body:
|
| help
| subscribe ibis <optional e-mail address, if different>
| subscribe ibis-users <optional e-mail address, if different>
| unsubscribe ibis <optional e-mail address, if different>
| unsubscribe ibis-users <optional e-mail address, if different>
|
|or email a written request to ibis-request@eda.org.
|
|IBIS reflector archives exist under:
|
| http://www.eda.org/pub/ibis/email_archive/ Recent
| http://www.eda.org/pub/ibis/users_archive/ Recent
| http://www.eda.org/pub/ibis/email/ E-mail since 1993

|------------------------------------------------------------------
|For help or to subscribe/unsubscribe, email majordomo@eda.org with just

|------------------------------------------------------------------
|For help or to subscribe/unsubscribe, email majordomo@eda.org
|with just the appropriate command message(s) in the body:
|
| help
| subscribe ibis <optional e-mail address, if different>
| subscribe ibis-users <optional e-mail address, if different>
| unsubscribe ibis <optional e-mail address, if different>
| unsubscribe ibis-users <optional e-mail address, if different>
|
|or email a written request to ibis-request@eda.org.
|
|IBIS reflector archives exist under:
|
| http://www.eda.org/pub/ibis/email_archive/ Recent
| http://www.eda.org/pub/ibis/users_archive/ Recent
| http://www.eda.org/pub/ibis/email/ E-mail since 1993

This archive was generated by hypermail 2.1.8 : Tue Oct 12 2004 - 21:05:51 PDT