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calculate single-sided PCB transmission line impedance?

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

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  1. Joop

    Joop Guest

    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

    Download the milmega RF calculator, it has a line calculator.
     
  3. Hello Joop,

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

    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 Larkin

    John Larkin Guest

    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. Joop

    Joop Guest

    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
     
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