From: Ron Miller ([email protected])
Date: Fri May 19 2000 - 13:03:51 PDT
lee
If you are referring to other signal pairs "spreading these
signals makes sense". If you are referring to the two wires
within a differential pair you are in trouble.
Ron Miller
Ritchey Lee wrote:
> When the data rate gets very fast, ala 2.5 GB/s, this "crosstalk coupling" has
> an errosive effect on edge rate and jitter. In such cases we spread the signals
> out so there is little or no coupling. It probably has some errosive effect at
> slower data rates as well, but there is more timng margin, so less worry.
>
> Lee
>
> Doug Brooks wrote:
>
> > Differential signals are a special case of crosstalk coupling where the
> > correlation between the signals is (a) known and (b) perfectly correlated
> > with each other with (c) a correlation coefficient of -1. In this special
> > case, you WANT the crosstalk coupling --- it works in your favor. So you
> > want the traces to be as close as possible (practical).
> >
> > To see some of the mathematics of why, see the article "Impedance
> > Terminations, What's the Value" on our web site at
> > http://www.ultracad.com
> >
> > Doug Brooks
> >
> > At 09:37 AM 5/15/00 -0700, you wrote:
> > >Hi everyone,
> > >
> > >I have a simple question about trace layout design for a differential clock
> > >signal pair of high-speed CMOS memory packages. I have two design
> > >guidelines for that as follows:
> > >
> > >1. SPACING between a differential clock signal trace pair must be
> > > MINIMIZED as well as matched in length in order to reduce noise.
> > >
> > >2. Differential clock signal trace pair must be matched in length in order
> > > to achieve matched electrical characteristics, but SPACING between
> > > them must be MAXIMIZED in order to reduce crosstalk noise.
> > >
> > >Which do you prefer?
> > >
> > >Thanks and regards,
> > >
> > >Brian
> >
> > .
> > ************************************************************
> > Doug Brooks' book "Electrical Engineering for the Non-Degreed
> > Engineer" is now available. See our web site for details.
> > .
> > Doug Brooks, President [email protected]
> > UltraCAD Design, Inc. http://www.ultracad.com
> >
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--
Ronald B. Miller _\\|//_ Signal Integrity Engineer
(408)487-8017 (' 0-0 ') fax(408)487-8017
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