[SI-LIST] Re: Differential Impedance; Traces w/o Ref Plane
- From: "D G" <dgun@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 17 Dec 2002 03:29:57 +0800
Ege,
You are correct that accuracy (more probably simulation time) could be impaired
by using large problem spaces. It depends on the simulator.
You are also correct about modeling the 2 traces as a single transmission line.
However, some simulators force a reference plane. In that case, you can move
the reference plane far away (if your physical design warrants it).
- Daniel
From: Ege Engin <engin@xxxxxxxxxx>
> Bob,
>
> if there are only 2 conductors (i.e., no nearby reference conductors),
> then the differential impedance is actually not defined. I would model
> these 2 traces as a single transmission line. Daniel's idea is also very
> interesting. In this case, the accuracy of the simulator could decrease
> due to the big problem space.
>
> Ege
>
> D G schrieb:
> >
> > 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)
--
Daniel
ZZZ-dgun-ZZZ-@xxxxxxxxxxxxxxx
(remove the Z-'s to reply--they're what I do when I read spam)
--
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