RE: [IBIS] Question regarding V-t tables

Bob,

This is an interesting "response", because according to the
IBIS specification, a model like that is still perfectly legal...
So to cover this, do we need to write a BIRD that says we should
not make any models that way? Right now there is nothing that
would prohibit something like this.

Arpad
================================================================

-----Original Message-----
From: Bob Ross [mailto:bob@teraspeed.com]
Sent: Wednesday, September 08, 2004 5:30 PM
To: Muranyi, Arpad
Cc: ibis@eda.org
Subject: Re: [IBIS] Question regarding V-t tables

Arpad:

I would expect some EDA tools to reject V-T tables with the same
R_fixture/V_fixture values because of processing equation singularities.
To avoid some EDA tool dependencies (both positive and negative), the
best approach is to use [Model Selector] to set up different data
pattern situation of interest.

Bob

Muranyi, Arpad wrote:

> All,
>
> I just realized something regarding the V-t tables in IBIS that raises

> a question in my mind.
>
> The spec says that we can have up to 100 V-t tables. It doesn't say
> anything on how Vfixture and Rfixture should be selected for these to
> make a good model.
>
> Many simulators can only support the first four tables, but I am aware

> of some which can make use of all of them. As far as I know, the
> algorithms which make use of all of them assume that the additional
> tables generated with the various Rfixture and Vfixture values provide

> a better understanding for how the buffer reacts to various loading
> conditions.
>
> What I would like to find out is this: What would happen if an IBIS
> file had multiple V-t tables with repeated Rfixture and Vfixture
> parameters, but different waveform shapes? (This ***CAN*** happen
> nowadays with advanced buffers which exhibit data pattern dependent
> behaviors). Obviously, given the current spec, the tool wouldn't know

> when to use which table. Would this be a good reason to write another

> BIRD for some additional subparameters for the V-t tables?
>
> Arpad

--
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
121 North River Drive              13610 SW Harness Lane
Narragansett, RI 02882             Beaverton, OR 97008
503-750-6481                       503-430-1065
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bob@teraspeed.com
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