Ivan,

There is another option. The MSC1210 can give you the performance you want in an integrated package. If we look at the same 4 Hz data rate (15 Hz data rate) and a gain of 32 (+/- 78 mV) the decimation ratio will be 1023. That will give an ENOB of about 20 which is 149 nV of RMS noise. That can be improved by doubling the modulation clock and using a decimation of 2000. With that you will have an ENOB of 20.3 or 127.5 nV. You will get that same performance whether you have the processor running or not.

It is unfortunate that the characteristics in the data sheet are specified in ENOB. ENOB = 24 - log2(STDlsb). We will be changing that in the future to give the information in volts RMS.