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

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From: Degerstrom, Michael J. (degerstrom.michael@mayo.edu)
Date: Mon Apr 16 2001 - 09:13:35 PDT


Paul,

Yes I understand your comments regarding jitter. The point
that I was making was that simulations made with the w-element
show very little DJ. If the DJ is caused mostly by
the non-uniform delay then the w-element model is not
doing its job correctly. Or perhaps I never modeled a
scenario such that the data rate, bit pattern, and
cable parameters taken collectively were sensitive to
DJ. One possibility - I usually model short lossy
pcb paths instead of longer cables and the longer paths
would probably be more susceptable to non-uniform delay effects.

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: Sunday, April 15, 2001 9:47 AM
> To: Degerstrom, Michael J.
> Cc: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Attenuation and Delay on a PCB Trance
>
>
> 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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