Re: gEDA-user: Trace impedance calculations in PCB

[Jeffrey Gregory <gregory.jeffrey@xxxxxxxxx>]

On Thu, Feb 12, 2009 at 1:41 PM, Gabriel Paubert <paubert@xxxxxxx> wrote:
>> 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.

Obviously this would have to be specified, that is easy.

> 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.

A tool doesn't not need to handle every edge case in order to be
useful.  As a designer, you need to be aware of when you are doing
things outside the tools knowledge.  It sounds like the best way to
add this to pcb is to let pcb export to a standard format which can be
loaded into other packages for varying levels of analysis.  Then as a
next step, the output of the impedance calculator could be used by pcb
as part of DRC.

Thanks for all of the pointers to various tools.
-Jeff


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