Filtering of VDDA pins on microcontrollers?

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Hello. On some MCUs, the supply pins of the analog circuitry are separated from the digital circuitry. I assume this is to allow for the possibility to supply the analog circuitry with a cleaner supply to increase accuracy? My question is, is it common practice to filter the VDDA pins of a mcu and how much increased accuracy can be gained from this? I know this will depend on a lot of factors, but I would like to hear some thoughts
 

Hi,

I´d say there is no general answer for your question.

It´s hard to describe the noise on digital_VCC.
Let´say 10mV RMS noise can be a single sinusoidal lowr frequency or it can be much higher and fast spikes.
If the time where the analog signal is being captured meets a quiet piece of VCC, then then result is clean, but if it meets with an edge then the conversion result may be corrupted.

I recommend to read the datasheet. This is the source of information. No one here has better informations.
Look for:
* power supply rejection
* recommended decoupling circuit
* recommended PCB design

Klaus
 

Adding a PI filter composed by two capacitors and one ferrite bead may be a good practice. The filter will stop the noise propagation in both ways.
 

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