[SI-LIST] Re: Differential Impedance; Traces w/o Ref Plane
- From: "D G" <dgun@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 12 Dec 2002 02:11:09 +0800
Bob,
In practice, you will always have some influence from nearby ground/power
planes. If nothing else, the chassis or nearby metal in the area will
influence the trace. So instead of trying to eliminate the reference plane,
just move it far away from the signal traces. About 20 times the pcb trace
seperation should be adequate, but if you really want to be safe, you can move
it as far as the simulator will let you.
- Daniel
From: btarasew@xxxxxxxxxxx
> I am trying to calculate the differential impedance of two pcb
> traces (ie a balanced pair) when they are routed in the area of a pcb with
> NO power/gnd plane to use as a reference. The available tools that I have
> access to only treat the cases that include a reference plane; ie
> microstrip, stripline, edge-coupled traces over a plane, etc. I also
> tried digging into a few of my old ElectoMagnetics textbooks, but those
> formulas for parallel-plate transmission lines make assumptions that
> handle only the case in which the plate width >> separation distance. I
> am having trouble finding a transmission line model that reflects pcb
> trace geometries.
>
> Any helpful information, formulas, links to websites, etc., would
> be greatly appreciated.
>
> Thanks in Advance,
>
> Bob Tarasewicz
> Westell, Inc.
> ph 630-375-4461
> btara@xxxxxxxxxxx
--
Daniel
ZZZ-dgun-ZZZ-@xxxxxxxxxxxxxxx
(remove the Z-'s to reply--they're what I do when I read spam)
--
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