[SI-LIST] Re: Q on Trace Width and Jitter for Diff Pairs
- From: "Cuchulain" <jlipsius@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 6 Jul 2005 10:34:07 -0700
Charles,
Well, dang, it's just that dispersion thing. For any bit sequence, a spectrum
of frequencies is
present.
So, you have ISI due to freq. dependent loss. ISI will change at different
positions in the
pattern, and will be different for each pattern. There is even a small
freq.-dependence
of velocity on a single layer, since Dk has some freq dependence. The result
is DJ, the
jitter of edges due to data pattern-dependent loss.
A wider trace will reduce the skin effect's contribution, but the dielectric
loss portion is
still there. Changes in layer, microstrip to stripline, also contribute due to
the velocity
difference between the two and the vias, which introduce reflection, insertion
loss and
- at some point - resonance. More DJ.
The "contradiction" isn't real, but imaginary --- now lose that loss tangent.
:-0
-John
----- Original Message -----
From: "Robert Sefton" <rsefton@xxxxxxxxxxxxx>
To: <Charles.Grasso@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Tuesday, July 05, 2005 3:22 PM
Subject: [SI-LIST] Re: Q on Trace Width and Jitter for Diff Pairs
> Hi Charles -
>
> Nobody has really addressed the jitter question. It doesn't seem to me that
> jitter is directly related to signal loss, regardless of whether the loss
> comes from skin effect or the dielectric. But DJ is directly affected by
> reflections caused by impedance variations, correct? Widening traces
> decreases the impedance variation caused by imperfect etching, which could
> decrease DJ. That's my best guess anyway.
>
> Regards,
> Bob Sefton
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Grasso, Charles
> Sent: Tuesday, July 05, 2005 11:39 AM
> To: 'si-list@xxxxxxxxxxxxx'
> Subject: [SI-LIST] Q on Trace Width and Jitter for Diff Pairs
>
> Greetings!
>
> I am stuck on understanding a contradiction - perhaps someone could
> "unstick" me?
> It is understood that (at high frequencies) the dielectric losses in a pwb
> dominates the losses of a transmission line. However, I have read in various
> publications that increasing the trace widths improves the jitter
> performance of a high speed serial link.
> I would have thought that as a trace width increases the effects of the
> dielectrics would be exacerbated.
>
> How does increasing the width of a trace improve the DJ of the link?
>
> Best Regards
> Charles Grasso
> Senior Compliance Engineer
> Echostar Communications Corp.
> Tel: 303-706-5467
> Fax: 303-799-6222
> Cell: 303-204-2974
> Pager/Short Message: 3032042974@xxxxxxxx <mailto:3032042974@xxxxxxxx>
> Email: charles.grasso@xxxxxxxxxxxx; <mailto:charles.grasso@xxxxxxxxxxxx; >
> Email Alternate: chasgrasso@xxxxxxxx <mailto:chasgrasso@xxxxxxxx>
>
>
>
>
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