Re: comments on BIRD 31.1

David, Hank, and IBIS Team:

Here are some comments on David's points. David, you have raised some
good questions, and some of my responses may be controversial.
However, I believe they are generally supportive and complimentary
to Hank's comments which I just received.

1. One of the underlying assumptions is that the IBIS mated model
captures the electrical contents of the connector without reference
to any external connections. I believe that the BIRD31.1 data can
be entered with that assumption. There are two further assumptions:

a. The contents of the BIRD31.1 structure can be reformatted into a
Spice Nodal Syntax.

b. It is up to the simulator companies to correctly identify the
rail connections (ground and power) and either do the analysis
correctly or to transform the model internally with that assumption.
Simulators vary in analysis capability and in purpose, so how this
is done may differ and may be more a function of the type of analysis
being done. Predefined rail connections may apply for certain classes
of mated models. But as mating components extent to thousand(s) of
contacts, this becomes impractical for the general case.

In the case of a Spice simulator, the rail connections can be applied
to the Spice connector model. To my knowledge, Spice Connector models
(which include coupling between pins) do not rely on predefined rail
connections. Therefore, for defining the IBIS data base for a mated
models, we should assume that the rail definition is external to the
mated model.

2. The mated model applies only to the "mated" configuration. So the
part of any finger that extends into the connector is included in the
mated model, and the part outside should be part of the circuit board
physical layout. I believe designer's assume that 1/2 of the finger
is inside the connector socket for optimal tolerance purposes. You
have raised a fundamental question regarding how the analysis program
should treat this situation and how any extending reference planes for
the fingers themselves would be accounted in the matrix mated model.
My presumption is that the mated model would be provided assuming
the suggested finger design configuration or separate models would
be provided for suggested variations.

3. I have some brief thoughts the measurement methodology question. I do
not believe any stated measurement defined extraction can be defined that
would work in all cases because an "ideal" test setup cannot be built.
Therefore, I would rather see crisp definitions of the parameters that
are needed which can be derived from any source - Spice equivalent structures,
field extractors, measurements, etc.

4. Field solver extraction is an expected option. Which one is used
may depend on the connector itself and what specification detail (such
as "edge rate") is required in the model.

For a closing comment, you have touched on some very difficult issues. With
respect to mated models one key concept is that the purpose is to provide
a MODEL that is suitable for the analysis that is being done. It will NOT
be a perfect replication of all aspects of performance - just as any
model is not a perfect representation of any particular device. So the
representation must reflect a reasonable compromise between complexity
and accuracy that makes it suitable for the intended purposes. The
questions you raise are useful to nail down the definition and scope of
the data contents of the mated model itself.

Bob Ross
Interconnectix, Inc.

> Subject: comments on BIRD 31.1
> To: ibis@vhdl.org
> Date: Thu, 11 Apr 1996 16:38:47 -0700 (PDT)
> From: "David Fogel" <dfogelx@ichips.intel.com>

> To: ibis@vhdl.org

> Subj.: Mated connector model, BIRD 31.1

> Regarding the proposed BIRD31.1 specs, I have the following questions/comments

> 1. Power and ground pins assignment will affect L,C values

> 1. Ground (and power) pins assignment will affect both the self LC values
> of a pin and the LC coupling matrix, based on the position of each pin
> relative to the ground pins.
> Consider the following three connector pins example:

> o o o
> ^ ^ ^
> | | |
> gnd 1 2(or gnd)

> The pins are 50 mils apart.

> When only the center pin is a signal and the other two are ground I get:

> SINGLE CONDUCTOR LC:
> ____________________

> i j Lij Cij Ze Zo Se So Fwdx Rvsx
> from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) (v/v)
> --------------------------------------------------------------------------
> 1 1 10.537 3.066 58.63 - 2.16 - - -
> ;

> and when only one side pin is a ground I get:

> DUAL CONDUCTOR LC:
> _________________

> i j Lij Cij Ze Zo Se So Fwdx Rvsx
> from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) (v/v)
> --------------------------------------------------------------------------
> 1 1 15.880 3.066 88.36 - 2.16 - - -
> 1 2 10.903 1.502 130.90 33.01 2.46 1.81 0.303 0.597
> 2 2 22.247 2.188 123.78 - 2.16 - - -
> ;

> Which clearly demonstrates the fact that you can not assign LC values to
> connector pins just by their physical location in the connector. You also
> need to know their position relative to the ground pins.

> This can be accomplished by depicting several most likely to be used signal-gnd
> configurations and providing the LC matrices to all of them. In a dual
> row connector you may end up with about 10 different combinations.
> This kind of information is precisely what's needed for high speed
> simulations and will make the modeling effort worthwhile from system
> engineering point of view.

> 2. Another level of complication in a mated model is the plug-in daughter
> card. The fingers themselves are part of a PC board. How long are those
> fingers in the mated model? is there any definition for it?
> The electrical characteristics can be affected by the presence (or absence)
> of a ground plane in between the daughter cards' top and bottom layers (the
> finger layers). How is this going to be reflected in the model?

> 3. Another issue is measurements and verifications of the model itself.
> Since we are talking about relatively small LC values, the test set-up
> can greatly affect the measured LC values.
> You may build a very elaborate test fixture at your facilities and obtain
> very precise figures. But can every vendor or user do the same?
> How do we decide which values are the right ones. I believe that we need a
> well defined measurement methodology to be included as part of the
> specs.

> 4. Another method for model development is to use the mechanical drawings and
> feed the physical dimension to a field solver. If precise mechanical dimensions,
> including the ER of the connector body, can be provided, then a field solver can
> be used to extract the LC matrices. This can be an alternative to the above methods.
> The issue here is which field solver to use? 2D? 3D? from which CAE vendor?
> etc.

> David Fogel
Received on Fri Apr 12 12:04:58 1996