I am designing a PCB for reading analog signal by the AD7732. I searched a lot to find tips which increase the precision and effective bit resolution. One of these tips is to segregate analog power supply and the Digital one due to switching noise of digital components. I want to Know:
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How to design a suitable powering circuits for an ADC. In AD7732 datasheet I did't see any new and different point exclusive for an ADC. It is worth collecting some tips around.
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Should I connect analog ground to digital ground? In some datasheets I read they should be connected. If this is true why do we segregate analog and digital power supplies? Doesn't this connection pass noise from one side to other side?
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Is two switching power supplies proper to use as analog and digital power supplies?
Best Answer
My thoughts on the matter:
*Make sure you have proper bypassing on VDD of the ADC. Close to the package as possible. On the other side of the board is usually nice. Combination of both large and small (10u & 0.1u).
*If you can separate the AGND and DGND, you'll see less ground noise from the digital circuits being injecting into the analog signals. You can use an isolator to bring signals between separate ground planes. That may be overkill though.
*Connecting AGND and DGND planes with a ferrite bead can help remove high frequency noise.
*Regarding power, I think either switching regulators or linear regulators are fine, just make sure you have appropriate filtering on the switching regulators and bypass caps on either type of supply.
Some extra links for reading: TI Application Note on grounding in mixed signal. Part 1 Part 2