In order to get best performance on tiny input signal, the pre-amp gain will be adjusted to properly load the trailing 20-bit sigma-delta ADC.

However, the high gain of pre-amp will introduce distortion. Give the lower speed operation, system may prefer to have a lower gain at preamp and let sigma-delta adc work harder to get the performance.

For nyquist adc, it is highly undesired to load adc very lightly, we are very motivated to load ADC near full DR.

What is the considerations for oversampling ADC in this case?

Thanks,
Neo