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Although there are plenty of free impedance calculators out there, I'm struggling to find one that can solve impedances for a differential pair using coplanar waveguide. Anyone know of any free software that can do that? The only one I was able to find was Si9000 and Si8000m by Polar instruments, but they aren't free.

Reason I'm interested is because I'm trying to route USB 2.0 HS signals on a 2 layer 1.6mm FR4 board and want to see if using coplanar waveguide will make it more practical (i.e. thinner traces).

Amr

Amr Bekhit
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  • What calculators have you tried (to save a thousand pointless suggestions)? – Andy aka Jul 07 '14 at 09:06
  • [atlc](http://atlc.sourceforge.net/) was mentioned in a recent [question](http://electronics.stackexchange.com/questions/117214/impedance-of-an-edge-coupled-coplanar-waveguide-with-ground/117240#117240), however I've never used it myself. – The Photon Jul 07 '14 at 16:06
  • Also the OP's geometry in that question might help you out. – The Photon Jul 07 '14 at 16:09
  • I tried this once :) It is possible but we had trouble because the reference portion of the coplanar waveguide had to be fairly fat compared to the traces so it took away a large section of pins from the chip. I want to say 1/4" maybe? Moving it away to make space defeated the point. Once we found out the true cost difference between a 4 layer board and a 2 layer board at our volumes we convinced mgmt to go with a 4 layer. By the time you factor in all the advantages including an easier time with EMI... It just made more sense. Good luck! – Some Hardware Guy Nov 04 '14 at 16:02
  • Oh and we figured out the waveguide by hand based on Wadell's book http://www.amazon.com/Transmission-Handbook-Antennas-Propagation-Microwave/dp/0890064369 I seem to have taken it home or I'd check the pages for you. – Some Hardware Guy Nov 04 '14 at 16:04

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Try TNT or TxLine.

Also note that your best bet may actually be VERY SHORT (few mm) traces, a thinner board or a 4 layer board :-)

Rolf Ostergaard
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    Thanks for your suggestions. Unfortunately, TxLine doesn't do coplanar waveguide for *differential* traces. I checked out TNT, but couldn't seem to be able to do the same with that either. – Amr Bekhit Jul 07 '14 at 09:34