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

From: Tom Dagostino <tom@teraspeed.com>
Date: Mon Feb 14 2005 - 14:48:45 PST

A series resistor model works well for terminations and it avoids having to
put it into the clamp characteristics. This also is the only way to do a
differential termination. One end of the resistor is tied to the I/O pin of
interest and the other end it tied to the ground, supply or diff pair pin.
Also, it makes playing with the termination value very easy.

Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
http://www.teraspeed.com
tom@teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Mirmak, Michael
Sent: Monday, February 14, 2005 2:33 PM
To: RODRIGUEZ_LECONA_RAMIRO; ibis-users@eda.org; ibis-info@eda.org
Subject: [IBIS-Users] RE: on-die termination

Ramiro,

Thanks for your message and for your interest in IBIS. The standard
approach I have seen is to add the on-die termination's effects into the
clamp curves, as you mention. You should, of course, take steps to
avoid "double-counting" of any single termination; in other words,
ensure that the effects of any single terminating device are not present
in both the [POWER Clamp] or [GND Clamp] keyword table data for the same
voltage points.

There is no requirement, per se, for all clamp curves to "reach the zero
value" as you state. For example, I may include a pullup resistor's
effects in the I-V table data for a model of type input. In this case,
if the termination resistor and the power clamp diode(s) are both
referenced to the same VCC supply, my IBIS model's [POWER Clamp] I-V
curves will likely pass through the origin, VCC-referenced. The [GND
Clamp] I-V curves will not cross through the origin (I will see a
negative current at 0 V, ground-referenced, due to the current flow
"out" of the pad), but there is nothing illegal in this. You would not
be required to use terminators, Rpower or Rgnd in this case.

I hope this helps!

- Michael Mirmak
Intel Corp.
Chair, EIA IBIS Open Forum

-----Original Message-----
From: owner-ibis-info@eda.org [mailto:owner-ibis-info@eda.org] On Behalf
Of RODRIGUEZ_LECONA_RAMIRO
Sent: Monday, February 14, 2005 2:12 PM
To: ibis-users@eda.org; ibis-info@eda.org
Subject: on-die termination

Hi all,

How can I include on-die termination for an input structure in an
IBIS
model?

Some people say that one way to include on-die termination is to
use
superposition and add the termination currents to the diode currents in
the
clamp sections. However this action is going to avoid that the clamp
curves
reach the zero value so the IBIS parser will report a error message.

Do I have to use the keywords Rgnd and/or Rpower?
When can I use "terminator" as my [model type]?

Thanks.
Ramiro

|------------------------------------------------------------------
|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 : Mon Feb 14 2005 - 14:51:16 PST

RE: [IBIS-Users] RE: on-die termination