A fully-differential CMOS low-pass notch filter for biosignal measurement devices with high interference rejection

A fifth-order fully-differential CMOS low-pass notch filter (LPNF) with high interference rejection is presented to provide an interface to the instrumentation amplifier (IA) in biopotential and bioimpedance measurement devices. The LPNF employs six operational transconductance amplifiers with differential difference input stage, which have low transconductances in nanosiemens range to enable the use of small capacitors that are feasible for on-chip integration. The filter design was simulated using IBM 0.13-μm CMOS technology. It has a bandwidth of 47.7 Hz, covering the electroencephalography (EEG) frequencies from 1 to 40 Hz with a notch of 73.2 dBc at the 60 Hz power line frequency. The fully-differential structure provides an inherent advantage of high common-mode rejection and high power supply rejection as reflected by system simulations (IA and LPNF) resulting in a common-mode rejection ratio (CMRR) of 101.3 dB and a power supply rejection ratio (PSRR) of 64.7 dB.