From: Rede, James (JRede@taqua.com)
Date: Tue May 08 2001 - 14:18:10 PDT
To the SI Good Guys,
I have been asked to design an edge-coupled differential stripline with no
for FR-4. This design is necessary to pass a Hi-Pot requirement of 1500
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
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
impedance is 100 ohms. If I then widen my plane-to-plane spacing to
I get something like 255 ohms. By trial and error, I was able to find a TST
that would produce a 100 ohm differential impedance at the 30000000000 mil
Qs: Is this a reasonable way to approach this problem? Is there a better
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
Signal Integrity Engineer
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