RE: [SI-LIST] : Attenuation and Delay on a PCB Trance

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From: Degerstrom, Michael J. (degerstrom.michael@mayo.edu)
Date: Fri Apr 13 2001 - 06:30:37 PDT


Paul,

I've noticed that w-element eye-diagram simulations show
very minimal jitter whereas your statements below suggest
to me that there should be jitter due to the internal inductance
effect. I haven't used the HSPICE w-element model for
a year or so but I have a technique to extract RLCG as
a function of frequency and the inductance was flat. I haven't
tried this yet for the new HSPICE w-element model with tabulated
RLCG vs. frequency.

I haven't directly looked into the lossy line equations but
in working with someone who has my impression was that the 1+j
factor was needed to provide a causal response. Also I thought
that the HSPICE w-element lossy line algorithm used the
1+j but it somehow does not affect the inductance versus frequency.

Mike

_______________________________________________________________
Mike Degerstrom Email: degerstrom.michael@mayo.edu
Mayo Clinic; 200 1st Street SW ; Rochester, MN 55905
Phone: (507) 538-5462 FAX: (507) 284-9171
WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html
_______________________________________________________________

> -----Original Message-----
> From: Paul Levin [mailto:levinpa@earthlink.net]
> Sent: Thursday, April 12, 2001 6:32 PM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : Attenuation and Delay on a PCB Trance
>
>
> To all concerned,
>
> Besides the attenuation effects on PCB traces, don't forget that the
> propagation
> delay is a function of frequency EVEN IF EPSILON-R IS CONSTANT.
>
> Few people realize that skin effect resistance is only a
> portion of the
> skin effect
> impedance. The Rs figure must really be multiplied by (1+j). This
> inductive
> reactance means that there is a bit more inductance
> (diminishing as the
> frequency
> increases.) Because of this, lower frequencies propagate more slowly
> than
> higher frequencies.
>
> This effect has nearly disappeared by the time one gets to 1
> GHz, but 1
> and 2
> Gbps data signals have frequency components much lower than a GHz.
> Consider
> Fibre Channel's "alternating disparity K28.5 pattern." This 20 bit
> pattern has
> quite a bit of energy at 1/20th of the data rate. Some others
> have told
> me that
> they have been able to create some (admittedly pathological) data
> patterns
> that resulted in even lower frequency content.
>
> Some years ago I computed the Fourier transform of the entire pattern
> and
> ran the harmonics through both the attenuation and phase
> characteristics
> of
> microstrip. It surprised people how well I could simulate the
> asymmetrical
> eye pattern. The analysis worked for shielded, twisted pair, too.
>
> Paul Levin
> Senior Principal Engineer
> Logic Innovations, Inc.
> A Xyratex Company
>
>
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