How big should an analog ground plane be?

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#1
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I'm laying out a 2-layer board (~5" x 5") for an ATmega2561 design and I'd like to use a ground plane for the ADC. I can't devote a whole layer to it so I was wondering if there's a minimum useful size. I was thinking of a square roughly the size of the CPU package, on the solder side just beneath the CPU, offset slightly to underly the ADC pins (I know about the single connection to digital ground). Is this adequate? Thanks.

Karl

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AFAIK ADC ground plane should be under all ADC equipment on that PCB. and it should be uninterrupted by digital signals (at least the interference must be minimized).

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The physical size of the ground plane is usually not the issue. Where it is and what is connected to it IS the issue.

One would like to put the analog ground under the peripheral analog circuits and use that ground for the ground connections for those circuits. Connect it to the system ground at a single point and don't let digital ground signals flow through it.

Jim

 

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