[IBIS-Users] RE: [SI-LIST] IBIS model for SSN/SSO?

Eric,

An excellent question, with a long history of discussion. This was one of
the origins of the quote "Kumar was right" that I've been known to use at
IBIS meetings.

As I understand it, an IBIS simulator doesn't really have enough information
to completely model the crowbar current (between power and ground) inside
the buffer during an output transition. The IBIS model tells us the voltage
and current at the output terminal, but we don't really know what crowbar
current is flowing inside the device. As Kumar put it (as far as I
remember) - there are a number of different solutions for internal current
that provide the same answer from the output perspective - and therefore,
the simulator is forced to pick one.

That was the basis for Kumar's contention that the V-T tables for I/O
behavior should actually be V-I-T tables - allowing the the simulator could
accurately model crowbar current, and by extension, SSO/SSN effects.

So ... as far as I understand the issue, you can't really count on an IBIS
model to accurately predict SSO/SSN, because part of the information it
needs is missing. If the assumption about internal currents the simulator
makes is correct, then yes, the answers may correlate well ... but there are
no guarantees.

If memory serves, others have presented studies on switching currents for
IBIS vs. SPICE models and reported good correlation. In any given instance,
I'd still recommend comparing the IBIS vs. SPICE results before undertaking
a lot of analysis work. In the case where the comparisons are favorable,
the advantage of doing the analysis with IBIS is obvious - speed and ease of
use.

Hope that helps,

Todd.

Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
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-----Original Message-----
From: Eric Hsu [mailto:owner-ibis-users@eda.org]On Behalf Of Eric Hsu
Sent: Wednesday, March 10, 2004 9:26 PM
To: Mirmak, Michael; Ibis-Users (E-mail); Si-List (E-mail)
Cc: Frank Dunlap
Subject: RE: [SI-LIST] IBIS model for SSN/SSO?

Hi Michael,

Thanks for your information. By checking IBIS model spec., I doubt whether
it can perform some information as spice netlist have, especial like short
circuit current from power to ground when buffer switching. That's why I
have the concern for SSN by IBIS model. Please correct me if I am wrong for
this point.

Best Regards,

Eric Hsu
Interface Technologies
NetLogic Microsystems, Inc.
450 National Ave.
Mountain View, CA 94043
650-961-6676 x198
This e-mail contains NetLogic Microsystems, Inc. Confidential information

-----Original Message-----
From: Mirmak, Michael [mailto:michael.mirmak@intel.com]
Sent: Wednesday, March 10, 2004 6:02 PM
To: Eric Hsu; Si-List (E-mail)
Cc: Frank Dunlap
Subject: RE: [SI-LIST] IBIS model for SSN/SSO?

Eric,

Thanks for your interest in IBIS. At the most recent US IBIS Summit
(February 2, in Santa Clara), Raymond Chen of Sigrity presented on SSO
issues, including the use of Cdie, and IBIS.

You can find all of the summit presentations at the following URL:

http://www.eda.org/pub/ibis/summits/feb04a/

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

-----Original Message-----
From: si-list-bounce@freelists.org [mailto:si-list-bounce@freelists.org]
On Behalf Of Eric Hsu
Sent: Wednesday, March 10, 2004 5:27 PM
To: Si-List (E-mail); Ibis-Users (E-mail)
Cc: Frank Dunlap
Subject: [SI-LIST] IBIS model for SSN/SSO?

Hi expert,

Is anyone have experienced to run SSN/SSO simulation by IBIS model? I am
=
curious about how much difference by using IBIS model vs. SPICE
model.=20

Best Regards,

Eric Hsu
Interface Technologies
NetLogic Microsystems, Inc.
450 National Ave.
Mountain View, CA 94043
650-961-6676 x198
This e-mail contains NetLogic Microsystems, Inc. Confidential =
information

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