xl97:
and what is this 'stale reference' for analog comment mean? can you explain a bit more please?
The 328P has a built in regulated 1.1 volt reference for the A/D converter. It will be 1.1 volts regardless of VDD.
If you use a plain 3.6 volt coin cell and select the internal reference, it will work... no regulator needed (and besides, any regulator just wastes the excess power as heat... even switchers).