RE: [SI-LIST] : Z Odd-mode, edge-coupled, 50ohms?

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From: cadpro2k@dacafe.com
Date: Wed Jan 17 2001 - 10:43:27 PST


Hi all,

Then... Could someone please tell me (any guidance is appreciated) in
layman's terms how I "might" route the differential traces, #1 using
microstrip; and #2 doing it stripline. I'm working a board with GETEK
material, it has a couple .1mm BGAs and many, many, many differential
pairs. I've done some preliminary calcs (using Polar Instr. CITS
software), and come up with .008" lines with .008 spacing and .024"
spacing between the pairs, routing on the microstrip layers. I'd like to
go smaller, and possibly decrease the dielectric to the plane layer, but
I've heard there "might be" crosstalk problems. Anyone?

I'm especially interested in routing these on stripline layers, but I've
heard that's not a good practice either. Help?

"This is just the beginning..."

Thanks for all your help.

Mitch
Sr PCB Designer
San Diego, CA

(P.S. I've got most all the articles I need, from Lee Ritchey's to
Mentor's App note, to Eric Bogatin's stuff to UltraCad's stuff, etc.
etc., but I need something in PCB layout terms. Thanks)

---------Included Message----------
> Date: Wed, 17 Jan 2001 09:58:42 -0800
> From: "Neffody Kraskoff" <Neffody.Kraskoff@Plexus.com>
> Reply-To: "Neffody Kraskoff" <Neffody.Kraskoff@Plexus.com>
> To: "'cadpro2k@dacafe.com'" <cadpro2k@dacafe.com>
> Subject: RE: [SI-LIST] : Z Odd-mode, edge-coupled, 50ohms?
>
> Hi Mitch,
>
> What type of driver technology are you using, is it LVDS? If so
then LVDS
> traces are 100ohm differential.
>
> If the 100ohm terminating resistor connects to the pos and neg
signals of
> your differential pair like so:
>
> -------------DIFF_sigP---------.---load pin (device)
> |
> /
> \ 100ohm R
> /
> |
> -------------DIFF_sigN---------.---load pin (device)
>
> Then your required trace impedence must be 100ohms differential
(matches the
> resistor value).
>
> Its extremely unusual to have 50ohm single-ended lines on the
same trace
> layer with 50ohm differential. Usually, its 100ohm differential
and 50 ohm
> single ended.
(snip)
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