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Cross section tool and impedance calculations

TH Designs

I ran into something the other day and have been working with tech support on, but thought I might get some answers here.

Four layer board, two inner layers set to planes (and shield) FR4 material.

In the Setup - cross section tool, when I try to calculate the trace width based on a given impedance and stack up, the impedance is always 60 ohms. For example, I open the cross section tool and select Show Single Impedance.  The default impedance shows as 60 ohms. If I try to change it to 50 ohms by manually editing the cell, it resets to 60 as soon as I click out of the cell.

If I try to change it by using the drop down boxes at the bottom of the window; Layer Type - Conductor; Material 1oz cu; Field set to - Impedance; Value Set to - 50; then select "Update Fields", nothing happens.

We tried multiple things yesterday. I even sent the board file to tech support and it works just fine for them (figures.....)

I tried it on a different computer at my home office and the impedance is displayed in exponential format, not in ohms.

A couple of screen shots:

  • oldmouldy
    Which exact version are you running Help>About in PCB Editor? I don't think that you are going to see the values update if you don't have any conductor layers that match, also the default materials.dat has 0 for some of the conductor thicknesses. When the "Update Fields" runs, you should see the "Field Solver bem2d" messages in the Command Window. It seems OK when I try this....
  • budnoel

    Hi TH - For whatever it's worth, I'm running 16.5 and here's a screen shot of my results.

  • TH Designs

    I'm at the latest ISR. Just spent some time on the phone with tech support. We tried many things, he is going to forward it to Cadence. Stumped..........

    I do not see anything run in the command window when I hit update fields.

  • TH Designs

    Bud,  

    Your results are exactly what I would expect to see and what they see at tech support. I wonder if something went amiss with my install..........

    Tom

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