I am currently working on the design of a reference buffer for a Sigma Delta.
I came across the TI ADS1248(datasheet). It seems that the chip can accept negative voltage references below ground (AVSS-100mV), as well as postive voltage references above AVDD (AVDD+100mV).
Doing this with a normal unity gain OPMAP would seem impossible (cannot drive the outputs completely to either rail). Does anyone have some sort of idea, of how such a thing can be accomplished? Seems a swtiched cap front might be able to do it, albeit at the cost of an input current.

Thanks!