[SI-LIST] AW: Impedence of Differential Pair Not Over Plane (Revised)

Hello Ray,

see Brian Wadell's Transmission Line Design Handbook chapter 3.4.6 "copla=
nar
strips" for the formula. My bet: 0.6 mm with a spacing of 0.2mm and epsr=3D=
4.5
. Yes, they are wide.

Thomas

-----Urspr=FCngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]Im Auftrag von Ray Gordon
Gesendet: Dienstag, 25. Juni 2002 11:46
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Impedence of Differential Pair Not Over Plane
(Revised)



Apologies for posting this twice. I made a fundamental mistake in the
original posting!
-------------------------------------------------------------------------=
---
----------

 Is there a formula for calculating differential impedence over an
(adjacent)
co-planar pair of tracks that are NOT routed over a plane layer?

 I am looking for 100 Ohms (PCB is 1.6mm FR4).

As a guess (based on a 2-wire transmission line in air)  I would estimate
that a track width to spacing ratio of approx  4 is required. If this is
correct then quite wide tracks will be required.

Can a reasonable transmission line be made in this manner?

 Thanks for your help.


Best Regards,

Ray Gordon                      ray@xxxxxxxxxxxxxxxxxx

Scene Double Ltd.            Tel:  +44 (0)20 8386 9001
Vision House                    Fax: +44 (0)20 8386 9002
Station Road
Borehamwood
Herts.  WD6 1DE
UK.


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