# calculate single-sided PCB transmission line impedance?

Discussion in 'Electronic Design' started by Joop, May 28, 2007.

1. ### JoopGuest

I wondered if trace on a single sided PCB could be optimised to
resemble a 50 ohm transmission line. It will be enclosed largely
between ground areas.

But looking around on the web I have so far only found dual layer
calculators for microstrip or striplines with ground planes.

Does anybody know some calculator, reading material or an simply
example?

Cheers,

Joop

2. ### Guest

Hello,
What you want is a co-planar waveguide.
http://www.maxim-ic.com/appnotes.cfm/an_pk/2093

3. ### Helmut SennewaldGuest

Hello Joop,

The program TXLINE can calculate the impedance for a CPW with
or without a ground plane.

I just tried the TXLINE-program for CPW with FR4(Er=4.5).
Z=50 Ohm, no ground plane
W=2mm, gap=0.25mm
Z=50 Ohm, no ground plane
W=3mm, gap=0.35mm

Best regards,
Helmut

CPW=Coplanar Waveguide

4. ### John LarkinGuest

Appcad will also do cpw, with and without flip-side ground plane.

Increasing the gap eventually produces the single trace, single-sided
board case. In older versions of Appcad, as the gap increased the
impedance started going back *down*, but they've fixed that.

Lots of formulas and many programs produce goofy numbers when the
situation deviates from their sweet spot. Negative impedances are a
dead giveaway that something isn't right.

John

5. ### JoopGuest

Thanks, at least I know the right terminology now.
Always nice to be buzzword compliant ;-)

While trying TXLINE I quickly get an error that the substrate height H
should be > 2(w+2g).
Your values only can be reached with super thick PCB material (6mm or
so). What did you specify to get to these numbers? Perhaps I am not
operating the program right.

Joop