AD7998 datasheet says that the voltage range for external reference can be any between 1.2 and VDD. I acquired an eval-ad7998 board and rewired one of the digital potentiometer to work as the external reference voltage at 1.0 vcc (my magic number). The noise was increased but it seemed to work just fine. The idea was to increase conversion precision but I am not sure if that is ok. I'm pretty much copying this board circuitry to read 8 pressure sensors and here are my questions:
1- It is ok to work with 1vcc for reference voltage? If so which ADXXX can provide me that reference?
2- The OP AMPs (AD8691) in the eval-ad7998 are set for unitary gain. What's the point here, impedance matching? Noise reduction?
3- What if I do not mess with the 2.5 vcc reference voltage and instead set up the OP AMPS with some gain that fits my application?