Hi Lakshmi,
What i mean from your schematic, the V1x- is named as Func Gen Gnd, please try to connect this pin to AGND.
Connecting this pin to AGND makes the AD7609 as a single ended. When using the AD7609 as single-ended by connecting the Vx- to GND, it can only excercise half of the range of the input.
Regards,
Jonathan