[Fwd: RE: [SI-LIST] : Comments from your SI seminar]

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From: Ronda Faries (RFaries@mfi.com)
Date: Thu Oct 28 1999 - 14:45:58 PDT


I've been following this "thread" today and feel compelled to add that
Printed Circuit Design magazine began sponsoring the PCB Design
Conferences eight years ago precisely because our readers were faced
with many of the the same issues that still abound--e.g., the need for
more and better education, "disinformation" spread by so-called
"experts" who aren't, and rules of thumb that don't work for today's
high-speed designs. I wasn't around for those early conferences, but
during the last three years I've watched our conference classes improve
and change to meet today's high -peed, EMC and SI concerns and I'm very
pleased to have assisted Conference Chairman and PCD Publisher Pete
Waddell line up the speakers for PCB West 2000 (March 20-24 at the
Westin in Santa Clara).

I won't post the planned conference class list here and turn this into a
commercial, but I do urge everyone interested in additional education on
relevant topics such as high-speed design, EMC, SI, RF and microwave,
DFM, bypass and decoupling strategies, data busses, powerplane
structures, thermal analysis, PCB stack-up, and crosstalk to bookmark
www.pcbshows.com, and check back in a couple of weeks for the complete
PCB West 2000 course listing.

Regards,
Ronda Faries
Editor in Chief
Printed Circuit Design

-------- Original Message --------
Subject: RE: [SI-LIST] : Comments from your SI seminar (SendII)`
Date: Thu, 28 Oct 1999 13:23:29 -0700
From: Doug Brooks <doug@eskimo.com>
Reply-To: si-list@silab.eng.sun.com
To: si-list@silab.eng.sun.com

At 03:30 PM 10/28/99 -0400, you wrote:
> I have read an article recently that states that the use of
>specifying the differential impedance of two traces on a circuit board is
>unnecessary. The only thing you need to worry about is the individual trace
>impedance. If you need a differential impedance for two lines to be 100
>ohms, just use two 50 ohm lines rather than using two signals whose
>differential impedance is 100 ohms. Also when connecting a 110 ohm twisted
>pair to PCB you should just connect it to two 55 ohm traces to achieve the
>110 ohm differential impedance. I have done enough research to draw my own
>conclusions, but I would like to get the reaction from people in this forum
>regarding this issue.
>
>Thank you,
>
>Paul Denomme
>Viasystems Inc.
>

You might be interested in my column "Impedance Terminatios" in the June
99
issue of the magazine, reprinted on our web site. It shows that we
ALWAYS
must consider adjacent trace coupling (the bad news) but that most of
the
time the degreee of coupling turns out to be negligible (the good news)

---
unless there is close differential or common-mode coupling.

Doug Brooks . **************************************************** Doug Brooks, President doug@eskimo.com UltraCAD Design, Inc. http://www.ultracad.com

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