From these specs that you provide it appears that your goal is to achieve measurements with at least this number of quantization levels:

# levels = 1500 / 0.1 = 15000.

If you throw in another x10 to try to help you get down to the desired accuracy of 10% of minimum level that translates to 150000 total reading counts. That sounds like an A/D converter of at 18-bits.

Have you attempted to calculate your total error budget to help to understand where in your proposed architecture you will be hurt by the errors such as gain error, gain drift, offset voltage errors and so forth?

Even the AD621 with its seemingly nice 0.15% total gain error corresponds to 6

One A/D count out of 150000 corresponds to:

1/150000 = 6.66E-6 or 6.66E-4% = 0.00066% of full scale.

The AD621 gain error alone is 227.27 times greater than this.

Looks like you are going to have to do everything possible to lower errors in each part of the system. In other words it looks like you have some nice challenges ahead. Have fun.

Michael Karas