Can anyone provide me reference circuit for AD620 for using it in differential mode, and how to calculate gain for it
Keep in mind that the AD620 came out in 1991, and if you have to redesign due to obsolescence,
it will cost you money. Look at some of the newer InAmps, such as AD8422, AD8421, AD8426.
Also, the 598 and 698 do math.
Are you going to do this in software? How fast does your system require?