Re: gEDA-user: pcb, how to make windows in ground and power planes?

[Stephan Boettcher <boettcher@xxxxxxxxxxxxxxxxxx>]

Stefan Salewski <mail@xxxxxxxxxxxx> writes:

> a) Minimize parasitic capacitance to any AC ground for all
> of the signal I/O pins. Parasitic capacitance on the output and
> inverting input pins can cause instability—on the noninvert-
> ing input, it can react with the source impedance to cause
> unintentional bandlimiting. To reduce unwanted capacitance,
> a window around the signal I/O pins should be opened in all
> of the ground and power planes around those pins. Other-
> wise, ground and power planes should be unbroken else-
> where on the board.
>
> Is there a way to to make such windows for pcb, or have I to build the
> planes from tiny rectangles? (I have a 6-layer pcb, all OpAmps are SMD,
> second layer is groud plane.)

I added corner points to the ground plane to leave windows under the
inverting inputs of AD8005 CFAs.  Its a mess, but the bords will
fly to Mars, as Ales just found out :-)

There can be multiple PCB layers in a group (physical layer).  How
about adding a flag for polarity, so we can have cutouts?  And
priority by stacking order?

Stephan


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