VDD Reference

Hello,

I'm confused what the NRF51422 uses for it's digital IO reference. So for example, If I use a 3.0V coin cell battery through its DC/DC converter:

1. What voltage does the DC/DC output going to the analog reference pin? 
2. What would the chip use for digital reference on VDD? 3V is obviously not a normal voltage, I would want 1.8V or 3.3V, etc. Is there a way to change this?

Thanks,

Tim