I'm seeking optimal/tested circuit that do the following
(1) I/P voltage up to +/-15V
(2) Low drift, good resolution range.
(3) Working bandwidth is essentially DC. AD7794/5 is ideal as it will reject 50/60Hz hums
(4) Rail to Rail as far as practically possible with minimum distortion.
(5) I/P impedance 1Meg but JFET op-amp cannot be used due to I/P voltage range limitation. This leave Bipolar or CMOS. This may be difficult so I can take 100K or 10K impedance for bipolar op-amp for better drift spec.
(6) +12V PSU available only (can use linear regulator for +5V). The 1st stage is an invertor with 2.5V offset, so it work on +/-15V input signal. It provides +5V signal into AD7794. The AD7794 has 2.5V VREF.
(7) AD7794 has GPIO which may be used to select AFE gains for better signal range
(8) SPI bus from AD7794/5 are digitally isolated to protect the MCU and rest of the equipment. .
Please advise optimal circuit or suggestion. I reviewed all your website and there is no solution for the above or could not find it.