RE: [SI-LIST] : Skin effect Modeling and Verification

Mellitz, Richard ([email protected])
Sun, 7 Sep 1997 20:53:10 -0400

Agreed, W models do well. The trick is to determine good values for the
Maxwell matrix. For example, traces less than 1/2 oz and less than 4
mils wide (i.e. PWB not cables) have significantly greater Rac than you
calculate from using a simple quadrangle geometry. What this does is
make ringing dampen are rate very similar to measurements.

I use W models when I get spice decks for I/O ring electronics from chip
mfgs to determine SSO effects. I don't like using lumped models for SSO
analysis which many vendors default to. We've got good agreement with
lab measurement here to.

Richard Mellitz, NCR

>From: Dr. Edward P. Sayre[SMTP:[email protected]]
>Sent: Saturday, September 06, 1997 11:47 AM
>To: Ray Anderson; [email protected]
>Cc: [email protected]; Edward Sayre; [email protected]; [email protected];
>[email protected]; Elco, Richard ; [email protected];
>[email protected]; [email protected]
>Subject: [SI-LIST] : Skin effect Modeling and Verification
>Dear SI/IBIS colleagues:
>As some of you may know, I and my colleagues Mike Baxter, Jinhua Chen, Tom
>Savarino and one of our client researchers, Dick Elco have been addressing
>the questions that Chris Simon posed in his recent message.
>The issue of time domain skin effects is at once one of the oldest questions
>in signal transfer going back to signalling in Morse code across the
>Atlantic, leading directly to the use of inductive loading coils and the
>theory of the distortionless line. At the same time, it is one of the
>newest and most important due to the clear emergence of differential
>signalling and Gigabit transfers desired in the HIPPI-64 and copper Fibre
>Channel contexts.
>Over the past year, we have been asking ourselves exactly how does one
>address the problems of skin effects in the time domain with arbitrary
>risetimes and non-linear sources and receivers. The frequency domain
>expanations for finite lines are not easily analytically specified from
>first principles, and a variety of conformal mapping and numerical methods
>have been applied successfully. The most readily studied is the round wire
>where anlaytic solutions are possible. Many authors, this one included, have
>developed concentric ring analogs for skin effects. We at NESA have
>extended these to finite elements for transmission line segmentation.
>(Design SuperCon'97)
>Recently, in investigations involving cabling and 1.0625 Gbps Fibre Channel
>signalling, we have had the opportunity to compare the .W model in
>Avanti/HSPICE to the NESA segmented model in both the time and frequency
>domain for long cables. To date, calculations have been made for both the
>NESA and .W model. Both the .W model and NESA models have proven to allow
>excellent modeling of real cable attenuation vs. frequency response (defined
>in the frequency domain from measurements). The issue for time domain
>simulations is the phase response, for it is the phase vs. frequency
>response which determines the dispersive characteristics of the transmission
>system. We have performed numerous time domain (.TRAN) simulations using
>both matched lab generators and realistic semiconductors, ECL and CMOS,
>driving these cable models. Variations in wire gauge are being considered
>as well as dielectric losses. As soon as we have experimental verifications
>of the simulation models, we will be publishing the results. Suffice to say
>so far that to date, the .W model seems to be holding up pretty well. [We
>refer the readers to Dr. Kuznetzov's notes on the .W model, avaliable from
>Avanti, for more details concerning the frequency modeling of Rs and G]. The
>trick is learning to relate the .W parameters to the actual interconnect you
>are working with. For best use of the .W model, (that to avoid a SWAG), you
>have to have frequenxy domain results for a sample of the interconnect.
>(The NESA model comes from first principles, but is limited in shunt loss
>Lastly, I wish to note that NESA has no affiliation with any simulation tool
>company and respects all trademarks, and other proprietary marking for
>product manes and features. We will keep the community informed as results
>Ed Sayre
>PS: If you are planning to come to the IBIS meeting we aresponsoring on
>September 18th, please let us know ASAP by e-mail so we can plan properly.
>| ------------------------------------- |
>| "High Performance Engineering & Design" |
>| Dr. Ed Sayre e-mail: [email protected] |
>| NESA, Inc. |
>| 636 Great Road Tel +1.508.897-8787 |
>| Stow, MA 01775 USA Fax +1.508.897-5359 |