About AD9231 Reference

Hi,

I would like to use AD9231. But,I have three question.

#1 When I use the outside Ref of AD9231with ADI product, What is highly precise, available Ref?


#2 ADI product does not have highly precise Ref in 1.0VRef output,
  in the case of 1.0VRef in using outside Ref , how should I make a circuit?

#3 For example, using ADR4520, can you make Ref of AD9231?

best regards

yuya