Subject: 3. [Begin_Cn_Model]... and other issues...

From: [email-masked]
Date: Thu, 13 Jan 2000 07:16:34 -0600

As stated....
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3. [Begin_Cn_Model]
   Does the optional SNR need to be restricted to SLM?  Could the format
   be generalized to "a:b" such as for 5:2.  Are the numbers restricted
   to integers?  Is there a need for a limit (e.g. 100:1.)

   I would prefer a syntax of the form:

     "[Begin_Cn_Model] ModelName"

   and then have the other entries as subparameters.  We already have
   a conflict with having the "required" ModelPinMap and ModelPhyMap
   entries that would not be used if [Begin_Cn_Auto_Map] is used.  Also,
   the single name argument is more consistent with all the IBIS keywords
   for named sections (e.g., [Component], [Model], [Define Package Model],
   [Begin Board Description], [Submodel]).
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SNR...  Do you mean SGR?  Assuming yes...
No, it doesn't need to be limited to SLMs.....  but,  from a technical
standpoint...  why worry about pin to pin coupling when the return path effects
have been removed?  I am sure that people do this all the time....  but I am
also sure that it will lead to incorrect system analysis.  I would really prefer
if this spec draws the line between models that represent return path effects
and models that do not in the SLM / MLM differentiation.  I really believe that
not doing this will result in greater end user confusion in the long run.  

[SoapBox_on]

For signal Integrity issues, we need to have a point where return path effects
are KNOWN accounted for in a simulation.  I propose that this be done in the
differentiation between SLM and MLM

I guess this assumes that the simulator (unknown to the user) or user does not
put perfect ground nodes on both sides of the connector)

[SoapBox_off]

Line Parameters / sub parameters... To me this is a formatting issue...  So what
ever 

I do not believe there is really a conflict with the mapping...

"Automap" is required for swath....  but although a model can be swathed ... it
isn't required for it to be used as a swath...   As such, a model that is
supplied could have both "fixed mapping" and automapping.

Fixed mapping is required for all models... while automapping is ONLY to be used
as an optional enhancement to the "fixed map" model.

Also, swathing is option for the following reasons
*  Model makers may not be comfortable with the concept.  Therefore, the model
maker would not want to include the option
* Some models CAN NOT be swathed

Reasons to REQUIRE a fixed map...
* All the above plus...
* Maybe a simulator vendor will not want to support the swath for technical
implementation reasons.
* A fixed map is a "Least Common Denominator?

_gus
[email-masked]
630-527-4617