Thanks Bill, but PCB Jack asked the question.
I liked it as well. I've seen many things tried on a PCB before and some
work and some don't. (You gotta try it sometimes if you have the time and
money.) I think it's very important to really look at the design
parameters, the board material, and the manufacturing allowances to see if what you
want to accomplish can really be done.
I can say from experience that creating a "twisted pair" in a PCB really
does not work the same as in a wire cable - not at all. ;-) But creating a
"transmission line" can be calculated. I don't know of any calculator that
doesn't have a return or reference plane either.
Cherie Litson, IPC-CID+/CMIT
Litson1 Consulting
PCB Design Solutions & Training
206-619-8844_ [log in to unmask] (mailto:[log in to unmask])
In a message dated 9/1/2015 1:10:26 P.M. Pacific Daylight Time,
[log in to unmask] writes:
Cherie asked, "Has anyone ever heard of routing differential pairs with no
reference plane? (on purpose?)"
I love questions like that... :) They make you think...
'Twin Lead' antenna wire is much like a 'differential pair' with an
impedance of 300 ohms without a 'reference plane'... the wires reference the
signal to each other. It's been used on televisions antennas for many, many
years... very low signal loss but higher susceptibility to noise than coax.
Another way to refer to a DIFF pair might be simply a 'transmission line'.
The next step would be a twisted pair... and then above that would be a
coaxial cable... The difference being in the shape of the return path conductor.
They still reference to each other through whatever dielectric that is
present... including air.
I don't know if anyone offers a calculator for that type of transmission
line...
:)
References:
https://en.wikipedia.org/wiki/Twin-lead
https://en.wikipedia.org/wiki/Transmission_line
William Brooks, CID+
Printed Circuit Designer
2747 Loker Ave West
Carlsbad, CA 92010-6603
760-930-7212
Fax: 760.918.8332
Mobile: 760.216.0170
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