The AD9650 data sheet quotes a gain thermal drift specification of 15 ppm/C. Assuming this is with the internal reference, what fraction of that number is the internal reference (which appears in Fig. 85 to approximately match this number) and what is due to other parts in the IC? In particular, to what could it reasonably be expected to improve with an arbitrarily precise external reference? The discussion of this on page 32 of the datasheet is somewhat nebulous.

Hello,

Unfortunately the datasheet does not elaborate on initial gain error/drift with and without the internal VREF.

In general, the internal bandgap VREF is the largest source of error hence using an external VREF with lower drift and higher initial accuracy will improve gain accuracy.

Regards.