Re: [SI-LIST] : Traces Impedance without plane

Aubrey Keith Sparkman (
Thu, 07 Jan 1999 09:36:06 -0600

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Although microstrip design is more common for controlled impedance boards they do require at least two layers. You may be able to do controlled impedance design in one layer if the wiring density is low enough. Investigate
co-planar wave guide design techniques.

Another technique to investigate is a balanced transmission line design such as flat twin lead. These designs result in higher impedances and do not require ground planes. However, one should take care when interfacing grounded
and ungrounded systems.

The best design method would depend not only on frequency, but also whether you had a digital, analog, or mixed signal design.

Good luck,

Michel Bazinet wrote:

> I would like to know how to calculate somes impedance between two traces if I don't have a plane on the board. One layer is enough to route this project.
> The impedance between the two traces should be 100 ohms and I do not have any ground on the board or from the cable.
> So, what can I do to have this impedance? Can I do this with a one layer board? Two layer board?
> Michel.

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