Subject: Connector spec swathing

From: "Chris Rokusek" <[email-masked]>
Date: Tue, 13 Jun 2000 10:39:29 -0700

Kellee & IBIS connector committee,

The DAC IBIS meeting was one of the best I've attended...well done!

I would like to request that the description of the "swath" matrix also
describe how to properly construct a fully-coupled matrix from the swath
matrix since there appears to be more than one "right" way to do it.

It would also be nice if the parser itself could perform this algorithm so
that a simulator may (if it so desires) just query the full matrix
regardless of how it was specified (swath, full, sparse, ...).

Best Regards,

Chris Rokusek
Innoveda

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From: chris <[email-masked]>
Date: Tue, 13 Jun 2000 13:29:00 -0700

Hello,

Chris is absolutely correct.  We need an unamiguous method of
building an arbitrary submatrix from the connector swath.  At
ICX we wrote a program that translates SPICE connector models
into full matrix models which our tool can use.  This is a
difficult process and needs significant input from the user.
There are many cases with ambiguities, sometimes without even
one clearly right answer let alone the case where there might
be more than one right answer.

The problem is best illustrated by considering what the SI
tool must accoomplish.  Given a particular situation to simulate
(which may include coupling to other nets) certain pins on each
component must be included in the simulation.  If any two (or
more) of these pins are situated such that using the swath for
both of them results in an overlapping set of pins (but not
coincident) then what is the coupling matrix that should be used?

Chris Reid

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From: Kellee Crisafulli <[email-masked]>
Date: Tue, 13 Jun 2000 14:03:52 -0700

Hi Chris, Chris,

I do like Chris Rokusek's idea of having the parser
create a full matrix.  This is not part of the specification
but rather would be part of the parser's specification.  It
would also create at least one unambiguous representation
of the matrix.

I do not agree that the method should be unambiguous however.
I do agree that the data must be unambiguous which I belive
it will be when we are finished.  Mostly likely this is really
your concern.
The swath method is an approximate method.
All the connector companies I know of already uses this
method with the existing SPICE models; they just require
a manual operation by the user.
The IBIS swath method refines this more and allows it
to be automated for the first time.  There are many methods possible
some that interpolate, some that compress, some that decompress,
and some that constrain to only the swath.  These all depend
on the end goal and need for a given situation.  So forcing
a particular type of conversation may lock out some uses of
the model.

best wishes
Kellee

> > regardless of how it was specified (swath, full, sparse, ...).

---------------------------------------------------------
Have a great day....
Kellee Crisafulli
HyperLynx, a division of Pads Software Inc.
SI,EMC,X-talk and IBIS tools
E-mail: <mailto:[email-masked]>
web:    <http://www.hyperlynx.com>
---------------------------------------------------------

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From: Mike LaBonte <[email-masked]>
Date: Wed, 14 Jun 2000 10:38:08 -0400

I would like to add an illustration of Chris Reid's point, as I see it.
Here is an ASCII picture of a connector. The pins marked as 'X'
are those carrying the signals that the simulation product has
determined MUST be characterized and simulated. The '0' pins are
the other pins of the connector:

0 0 0 0 0 X O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
 0 0 0 0 X 0 0 0 0 0 0 0 X 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 X 0 0 0 0 0 0

Assume that the connector model uses a 3x3 swath with 1 left edge
and 1 right edge (5x3 total matrix size). Here is one possible
pattern for using the swath, where 'M' represents matrix middle pins,
and 'E' represents pins in an edge column, which must be terminated
by Cn_Z. The '?' pins are those that could be either an edge or a
middle, depending on which nearby swath it is considered to be "in":

0 0 E M M X E 0 0 0 E M M ? ? M M E 0 0 0 0
 0 0 E M X M E 0 0 0 E M X ? ? M M E 0 0 0 
0 0 E M M M E 0 0 0 E M M ? ? X M E 0 0 0 0

There is no single swath that can contain the 2 pins on the right.
But 2 swaths, each centered around one pin, will overlap. Most likely
the simulator will have to make some choice that does not fulfill the
intent of the model developer. Even the 2 pins on the left have some
ambiguity; I chose the pin in the middle row as my center point, but
the choice is not always obvious.

On the subject of centering a swath around a pin, a swath with an even
number of columns has four possible locations, giving four possible
simulation results, depending on which is chosen. This is because the
swath has no pin at the center, but has 4 pins equally close to the center.

Since simulators have to handle a full matrix anyway, I would have to
join Chris Rokusek in hoping for a solution that turns a connector model
into a full matrix.

Mike LaBonte
Cadence