THanks jbb for your feedback,
Anything below 100 Hz is not so crucial for me.
On the other side of the spectrum, I need a 3dB cutoff higher than 100 MHz.
THe servo DC seemed to me a good option since I'll have to treat about 1k channels with different offset. S no way to adjust the DC offset individually.
I'll be able to generate the rails I need. I had in mind +-5 V since the max absolute value ot the offset is 1 V and the sampling ADC will get differential inputs of [-1.25:1.25] V range.
Noise immunity is clearly crucial here. I'm dealing with a 16 Bits ADC (almost 14 effective bits) and the lower end of the ADC range is crucial for my application.
I had in mind the use of a dip switch to toggle from high to low gain (12 dB to 0 dB). Not sure that I can ensure the 100 MHz bandwidth with a dipswitch. the parasitic cap may be a showstopper.
David: thanks for the comment of LF CMRR, that could save my ass one day. I think sdouble mentioned a single ended input, so not a killer in this case.
Sdouble: yes, that sort of thing. The DC servo integrator has a low-pass characteristic; when you wire that into a feedback loop I think you effectively end up with a high pass filter. What’s the lowest frequency you’re interested in?
You could instead do a fixed DC offset with an analog subtraction and reference DAC / pot. This is basically what the ‘position’ knob on an oscilloscope does. Of course, it will need adjusting from time to time.
What supply rails do you already have on hand? And how do you need to control the gain? Variable, basic high/low switch?