Every signal path is a loop, consisting of the discrete trace that you normally regard as the "signal path", and the return side that follows either the ground or power supply return.

The correct answer to your question is - whichever will produce the shortest return path for each signal while keeping the digital and analog returns separated. How did you connect the ground fills to the inputs and outputs of the devices on the board? Are the device I/O traces on the same side of the board as the respective ground/power returns? How are the power supplies and devices bypassed? Ordinarily, in a mixed signal environment such as A/D or D/A, you keep the digital and analog return paths separated to keep the noise under control on the analog side.

So much for real engineering and hard science. For your non-critical application, you can probably get away with peppering the board with "a bunch of vias all over the place." This non-engineered way of handling the problem will probably keep you from having too many loops large enough to cause signal cross-coupling problems. The best engineered way would be to start over in the layout with proper regard to keeping the analog side separated from digital side.

Many books and articles have been written on the subject of analog grounding. There is probably a manufacturer's application note for the specific ADC you are using that will discuss grounding. Here are a couple of simple Internet references you can look at that will give you a few hints:


Regards - Harry

At 11:09 AM 7/17/03 -0700, you wrote:
hi there, this is a general PC board layout design question as opposed to a protel specific question - i hope noone minds too much

my question is this - i have a double sided board with ground fills on both sides - what is the best way to go about connecting these? the board is an audio A/D card (though not a fancy super high fidelity design by any means)

scattering a bunch of vias all over the place? or only connecting at a few key points ?

thanks for any advice/pointers to more information on the subject


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