An analog front end based on chopped signals highly immune to RFI

Amplifiers used in analog signal conditioning circuits are usually protected against electromagnetic interference (EMI) by means of filters placed at the PCB level. The literature is plenty of solutions aimed at keeping filters´ attenuation as high as possible in the widest possible frequency range, but actually such filters are less effective than expected because of the parasitic elements introduced by interconnects, therefore EMI can be propagated into ICs causing temporary or definitive operation failures. This can be avoided inserting EMI filters at the IC level and/or using circuit topologies intrinsically immune to EMI. This paper shows that the immunity to RFI of analog circuits based on feedback opamps is significantly improved if input signals are chopped before being amplified.