Prahlad J. Purohit wrote:
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...but I don't want to use that ICL7660 unreliable supply anymore I will use some other reliable and stable supply voltage source.

But is it GOOD ENOUGH, over your range of interest ? My guess is with Kai's choice of amp, and the PSRR of that amp, you should be fine (change the diodes) with what you had. You don't want 16 bit precision, you are after 7.

Steve