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

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From: Paul Levin (levinpa@earthlink.net)
Date: Sun Apr 15 2001 - 07:46:47 PDT


Dear Michael,

The jitter resulting from this non-uniform delay is what the Fibre Channel
folks call "Deterministic Jitter." It is not due to any random events;
rather
it is due to the patterns of the data and the various frequency components
required for the particular data pattern. There would be no deterministic
jitter, for example, in a pure clock signal. The K28.5 pattern with
alternating disparity went something like 11111001010000011010 and then
repeat.
You can see very easily the contribution at 1/20th of the clock rate.

Even without any random jitter, the basic shape of the eye opening was
determined by how all of the harmonics propagated, both amplitude and
phase.

Paul Levin
Senior Principal Engineer
Logic Innovations, Inc.
A Xyratex Company
_______________________

"Degerstrom, Michael J." wrote:

> 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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