Re: Differential mode analog active filter?



Jim Thompson wrote:


There is a high precision ADC with the differential input (SNR ~ CMRR ~ 100dB).

If we make the two identical analog filters for /+/ and /-/ paths, then the CMRR will suffer because of the limited tolerance of the components. I would expect problems mainly due to the accuracy of the capacitors.


I tried to design a schematic similar to the conventional filter but with the floating ground. A simulation shows problems with the CMRR and the frequency response; the bootstrapping of the power rails of the opamps towards the floating ground helps somewhat, however it rather complex and doesn't look as a very reliable solution.

What topology should be the good approach to the problem? Can you suggest a book, an appnote or any other information?


Take a look at the gyrator-based filter configurations on the SED page
of my website. You should be able to easily extend these to
differential.

Thank you very much for the good advice. Yes, the gyrator topology works well for the differential filter.

VLV
.