Subject: Frequency Dependent and Lossy

From: [email-masked]
Date: Wed, 24 Nov 1999 06:47:09 +0000

First, 

To the entire group...  I am sorry that I missed the last meeting.  I was fully
planning on being there...  had an unfortunate incident that came up that need
my immediate attention...

I will plan on being at the next meeting.

However, in the spirit of helping...  I would like to address a few of the
comments from the meeting notes:

This email topic:

"Stephen Peters and Arpad Muranyi asked several clarifying questions on
whether the (frequency dependent) conductance matrix was included, and Kellee 
responded that it was not.  Furthermore he stated that the decision to 
postpone losses was made after consulting with a number of internal technical 
experts."

In my mind there are two issues built into this statement:

1. Frequency dependence:  At this time a "FREQUENCY DEPENDENT COMPONENT" is not
built into the specification...  However...  CASCADED MATRICES are built in to
the specification.  The cascaded matrix allows the model to represent
asymetrical or symetrical filtering effects that are typically found in
interconnect structures with multiple discontinuities (i.e. allows you to
represent a pole/zero as they actually occur as the energy passes through the
length of the interconnect).  Thus representing each discontinuity on it's own..
in a series and/or stub configurations. As such, it is quite reasonable to
expect that by using a cascaded model, it is possible to extend the operation
point of a model to the limits of the performance limits of the interconnect
being modeled.

With BERKELEY SPICE models (no vendor specifi SPICE extensions required) , using
a cascaded modeling approach...  today, a 6GHz 3dB bandwidth is a typical
modeling requirement (9GHz. is also possible).  Yes this can be confirmed to
both frequency domain and time domain lab measurements.  

Further, I would also suggest that a frequency dependent component is really
something more than just a swept series resistance that varies as a function of
frequncy in a single lumped model.  As such, to do a true frequency dependent
model, something more like a behavioral model (s-parameters anyone?) would be
the most appropriate method of representation.

2.  Conductance matrix:  At this time a conductance matrix as such is not built
in to the specification.  I think that when this effect comes into play  (I do
not have supporting data, but my guess that conductance becomes significant at
frequencies greater 8 GHz.  ....at least in devices as short as connectors) that
the "s-parameter" solution would be the best solution to correctly implement
dielectric loss effects.

So why noy implement s- parameters now
*  Model complexity....  the connector matrix models that are setup in the
proposed connector specification can be in the 100's to 1000's of lines.  I've
seen (and created) mulitport s-parameter models that are 100x the size.  Of
course, this depends on the frequncy step size and frequncy range of the model.
*  We really  wanted to incorporate an unlimited pin size connector using a
"swath" as proposed in the specification.  As the s-parameter matrix is not a
"single value per coupling / self node" (like , for instance an inductance
matrix would be)...  I had no idea on how to handle the complexity of a swathed
s-parameter.  
* Many simulators that use IBIS models are time domain based...  the complexity
of adding s-parameters may be too difficult.
*  The proverbial , We approached the proposed specification with a "Walk before
you run philosophy".
*  We also wanted to focus on the connector models that are primarily available
today...  and be able to implement those as soon as possible into a new format.

_gus: 630-969-4617
[email-masked]

---

From: Ted Creedon <[email-masked]>
Date: Wed, 24 Nov 1999 09:06:09 -0800

You are right on.

Just a 400 mhz connector can cause problems due to inaccurate modeling therefore
inaccurate specification by the customer therefore lack of process control by the
vendor. And this is in addition to the Z0 change at the connector.

Two things will happen 1. the designers will get smarter and stop using high speed
connectors thus avoiding the problem and 2. Ibis will eventually figure out how to
model frequency dependent devices.

Sets of S parameters for N ports are the only comprehensive solution now because the
only accurate information available is from instruments or 3D field solvers. However
the condensation of the information into something useable (the S parameter sets can
be viewed as a (N-1)*ntables  dimensioned surface where N=# of ports, ntables=no of
frequency points for each Nport set of S parameters).  We're running into this
already for via modeling.

The problem of characterizing e' + je'' which vary with frequency is a area of
active interest. Particularly since many designers choose  to create this problem by
using FR4 rather than a good dielectric like Duroid or Kapton. Which is worse
because for FR4 boards e' and je'' are anisotropic - it varies with the fiberglass
mat orientation in XY and and may also vary in the Z direction. Don't forget you're
trying to control the electrical length to less than 100ps and keep the rise time
out of the quadratic range (RC line rather than LC).

As an example a large digital system could be flip chipped on a MCM - no PCI busses,
AGP busses, ISA busses or memory connectors with a microwave launch to the
keyboard/mouse and display. And satellite or fiber.
If one stops and thinks of the advantages in miniaturizing, lowering manufacturing
cost and simplifying simulation we might design ourselves out of a job.

ted