Nano-microvolt amplifier  + filters


I would like to amplify a very low signal. Typically, the signal is from 1mV to 9.8mV (so a range of 8,8mV).

This signal is coming from a voltage divider (between the ground and the two resistors).

This signal will be amplifie to reach an amplitude max of 3.3V.

The bandpass needed if from DC to 5-8Hz.

The amplified signal will be numerized in a 16 bits ADC.

I think my major problem is the noise, I'm afraid that the little variations will be covered by noise. I know that I won't be precise at one LSB but I want to do the maximum to minimize noise error and measuring very very little variations.

So I have questions :

- I selected two amplifiers, an AOP (AD8571) and an instrumenation amplifier (AD8237). I don't know what's the best choice for the application.

- I will filter to remove maximum noise in high frquency (>5-8 Hz).

     - It's best to filter before or after amplifier ?

     - I think to use 2nd order sallen-key active filter, is it reaaly best to have 2 cells to have a fourth order ?

- For the supply of the voltage divider, is it really necessary to use a low-noise/very precise voltage reference to minimize the noise at the source ?

Best Regards,

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