**From:** Rede, James (*JRede@taqua.com*)

**Date:** Tue May 08 2001 - 14:18:10 PDT

**Next message:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Previous message:**Rich Hovey: "[SI-LIST] : Signal Integrity Engineer Opening"**Next in thread:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Reply:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"

To the SI Good Guys,

I have been asked to design an edge-coupled differential stripline with no

planes present

for FR-4. This design is necessary to pass a Hi-Pot requirement of 1500

volts.

The differential impedance is to be 100 ohms for T1 frequencies (1.544MHz).

Four layers are present but no layers are power or ground. Let the board

thickness

be 62 mils +/-10%. Use 1/2 oz copper and assume that Er = 4.1.

I cannot use my Hyperlynx field solver because THEY TOOK MY DONGLE.

When I use an impedance calculator found on the web and specify 5-7-6 mils

(Trace-Space-Trace, TST) and a plane-to-plane separation of 30 mils, the

differential

impedance is 100 ohms. If I then widen my plane-to-plane spacing to

30000000000 mils,

I get something like 255 ohms. By trial and error, I was able to find a TST

of 20-6-20

that would produce a 100 ohm differential impedance at the 30000000000 mil

plane-to-plane

separation.

Qs: Is this a reasonable way to approach this problem? Is there a better

way?

How should this problem be done, even a field solver will not give an answer

without ground planes present? What about accounting for the board thickness

then air?

J.J. Rede

Signal Integrity Engineer

Taqua Systems

Hyannis MA

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**Next message:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Previous message:**Rich Hovey: "[SI-LIST] : Signal Integrity Engineer Opening"**Next in thread:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Reply:**Jian X. Zheng: "RE: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"

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