Hi,
-various types of analog sensor, not known in advance
-various type of MCU (not known in advance) with 12bits resolution SAR SAR ADC
"not known in advance" means there is no clear requirement.
When I design a circuit, then I first decide the requirements.
So you try to design a "most versatile" circuit. While this is a good idea -- it it hard to solve.
--> I strogly recommend to define your own requirements.
***
To your circuit.
Where do you see the benefit in using your OPAMP circuit?
I start with the drawbacks:
* increased supply current
* introduces noise
* introduces offset and offset drift
* introduces nonlinearities
* you need a "unity gain stable OPAMP" otherwise you risk oscillation
* output can not go to zero (assuming a VCC / GND supplied OPAMP)
* output can not go to VCC
Back to the benefits:
* higher input impedance:
but this get´s killed by the relatively huge input capacitor at the input. Thus the improvement is just at very low frequencies.
If you have a high impedance sensor, then you get an unknown cut off frequency. but "unknown" is no benefit in my eyes.
But if you have a low impedance sensor, then omit the OPAMP (maybe just use the 10k and 100n in front of the ADC) while improving overall performance (see drawbacks). Many ADCs are happy with 10k input impedance.
* honestly I don´t see any other benefit of the OPAMP here.
Don´t get me wrong: I often use OPAMPs, also in front of an ADC. When correctly adjusted to the sensor and the ADC then they bring benefits. But you have to be aware of the drawbacks, too ... and decide wheter / in which case they improve the performance.
****
Opamp circuits in front of ADCs are good:
* for gain setting
* to add DC offset
* to act as anti aliasing filter
* to act as differential to single ended converters
* to act as impedance converter
But they will never improve
* DC performance
* noise performance
* distortion
(In best case they can help to keep noise and distortion low)
Klaus