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

Eric:

I agree with Todd's response and add for reference that this issue
was considered years ago in a BIRD42.3 proposal.

   http://eda.org/pub/ibis/birds/index.html

The proposal documented additional I-T tables. However, there were
concerns ranging from technical robustness to model provider and EDA
vendor support.

Bob

Todd Westerhoff wrote:

> 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
> ============================================

> -----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
>
>
>

-- 
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Consulting Group LLC
2926 SE Yamhill St.                Device Modeling Division
Portland, OR 97214                 13610 SW Harness Lane
503-239-5536                       Beaverton, OR 97008
http://www.teraspeed.com           503-430-1065
bob@teraspeed.com                  503-246-8048 Direct
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