[SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines

THANK YOU!!!

A response absent of sarcasm and/or scorn, and with some useful
information.  A pleasant change from the recent postings on the forum.

Thanks Steve,

Jeff Loyer

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of steve weir
Sent: Wednesday, May 30, 2007 1:39 PM
To: voorhies@xxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IEEE1394/Ethernet Routing Guidelines

Randolph, I suggest any of the following four books would be helpful to
y=3D
ou:

Signal Integrity Simplified, Bogatin
High Speed Signal Propagation, Johnson and Graham
Digital Techniques for High Speed Design, Granberg
Right the First Time Vol II, Ritchey

Lee Ritchey self publishes so if you want Right the First Time  you will
=3D

need to go to www.speedingedge.com.  Your alternative is to rely on
PHY=3D20
manufacturer guidelines.

The basic guide that I can offer you is this:

* Loosely coupled pairs are easier to manage than tightly coupled=3D20
pairs.  If you don't specifically need tight coupling for density=3D20
reasons, you will be less likely to go wrong with loosely coupled pairs.
=3D


* The crude approximation for a loosely coupled pair is Zodd =3D3D
2*Zeven.=3D
 =3D20
Ie two loosely coupled 50 ohm traces will have about a 100ohm odd
mode=3D20
impedance.=3D20

* Maintaining a uniform impedance and matched electrical length will
do=3D20
much to get you were you need to go.  If you are a tiny bit sloppy,
it=3D20
shouldn't matter for a student project.  Your project doesn't have =
to=3D20
pass FCC part B, and it is unlikely that you have to support =
maximal=3D20
length links.

Eric Bogatin's book has some impedance nomographs.  However, there are a
=3D

number of free calculators around some better than others.  Google
for=3D20
impedance calculator and take your pick.=3D20

Good luck.

Steve.



Randolph Voorhies wrote:
> Hi Everyone,
>    I'm brand new not just to this list, but to the world of PCB
product=3D
ion in general.  I'm currently a masters student at USC in robotics and
h=3D
ave been producing some relatively simple PCBs for the past few months
us=3D
ing Eagle. I'm now working on a fairly complex project that involves
crea=3D
ting a custom baseboard for an XTX module (xtx-standard.org).  My formal
=3D
training is in digital electronics, computer architecture, and computer
s=3D
cience, so when it comes to signal integrity I'm pretty much at a loss.
=3D
Does anyone know where to find specific routing guidlines for
differentia=3D
l pair lines such as firewire and ethernet? I have read all sorts of
conf=3D
licting advice (differential impedence is crucial vs. differential
impede=3D
nce couldn't matter less, etc..), and have had a very difficult time
find=3D
ing exact numbers for trace spacing/individual trace impedence and so
on.=3D
 If anyone with experience has any advice that has worked for them it
wou=3D
ld be very very very much appreciated.
>
> Thanks so much,
>   Rand Voorhies
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