2.2 Analog Supply

AVR devices that have a built-in ADC may have a separate analog supply voltage pin, A_VCC. This separate voltage supply ensures that the analog circuits are less prone to the digital noise that originates from the switching of the digital circuits.

To improve the accuracy of the ADC, the analog supply voltage must be decoupled separately, similar to the digital supply voltage. AREF must also be decoupled. The typical value of the capacitor is 100 nF. If a separate analog ground (AGND) is present, the analog ground should be separated from the digital ground so that the analog and digital grounds are connected only at a single point (at the power supply GND).