I have a customer that would like to know the pluses/minuses of using a Vref 2.5V versus the 4.096V reference for the AD7663. I saw that the datasheet has performance characteristics for the 4.096V Vref, but not for the 2.5V. Have you done evaluation with both? Can you share your results? Any opinion on advantages, disadvantages would be great. i.e. performance over temperature, stability over time etc.
In a fully differential ADC driver. the VOCM pin should be connected to your Vref/2. Please see attached example schematic using the ADA4940-1 a newer part which I also recommend that can drive the AD7663. and then you can also use two single ended ADC driver like ADA4805 where the VCM(Vref/2) is connected to the non-inverting input of the ADC driver.