On Thu, Feb 12, 2009 at 01:27:37PM -0500, Stuart Brorson wrote: > > Are there any plans to add trace impedance calculations to PCB? If > > not, is there an argument against it or just that no one has time and > > interest? What alternatives do people use? > > As Joe pointed out too, PCB doesn't not know about the metal layer > separation distance, nor does it know the dielectric constant of your > insulating material. Therefore, it cannot do impedance calcs.
It's even insufficient, in my last microwave board the distance to the cover slightly affects the impedance (but also the coupling between tracks). Actually the cover is very low above the circuit, 1mm except in the area of the largest capacitors and above the microwave signal tracks where it is machined. It is really 3D and depends on things that PCB does not even want to know... Typically I also work the otehr way around. I compute all the physical parameters for the impedances I need and then I set the line width and clearance accordingly. Now I would like very much to have a way to tell PCB that two nets form a diffential pair and to be able to draw them at once. Regards, Gabriel _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user