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jheissjr

Separate Analog and Digital Supply

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A question for you EE guys...

I would like to make two separate voltage supplys, one for my analog circuitry and the other for my digital circuitry. Both are powered by one battery.

My question is how do you isolate (electrically) the grounds between each supply when they are both powered by one battery, in particular when using linear regulators (7805)?

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Hi, Jheiss Jr

<_< The only way is to use DC/DC insulated Converters ...

from Semiconductor Circuits inc. i.e.

Alain

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I wanted to isolate the grounds because I thought doing this would provide the best shielding possible between the analog and digital circuitry. I am using a 16 bit ADC so I thought this would be good practice in that it would isolate the ADC analog circuitry from the noisy digital circuitry. It sounds like I am wrong about this approach though.

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Your analog and digital gnds should be connected. This is done at a common low impedance point on your PC board in the power supply area. Beyond that, the analog and digital gnd must not be shared (mixed).

Getting full performance from a 16-bit ADC will require a very careful layout. I can't imagine using anything less than a 4-layer board.

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