Avoiding electrolytic capacitors in high-pass filters with sub-Hz cut-off

We need to design a HPF filter to AC couple a bipolar signal to a high gain amplifier. Any substantial DC left would saturate the amplifier, and thus it must be removed with the high-pass filter(HPF).

But the bandwidth of interest extends down to 0.1Hz and therefore the cut-off for the HPF should be way below 1Hz.

A simple first order solution would use a capacitor in series with a resistor.

Then C needs to be large to achieve a very low cut-off freq., but electrolytic capacitors can not be used as the signal is bipolar. Further, tolerances are poor for electrolytic caps, which would not be acceptable for our precision amp.

What are the best designs for this HPF which avoid electrolytic capacitors?

A possible solution seems to be to implement a second order Butterworth with a Sallen-Key architecture. The (two) Capacitors needed in this design (according to TI's Webench filter design tool) are smaller than the C called for for a first order HPF.

Is this a good way forward (increase order and use multiple stages to avoid large capacitors)?

Which are the established approaches to this problem?

Answer

A common way to deal with this is to use a "DC servo" circuit to cancel out the DC component. Build a low-pass filter to isolate the DC and then invert it and add it to the original signal. The advantage is that you can use high values of resistance and relatively low values of capacitance in the low-pass filter.