Frequency-bandwidth-tunable powerline notch filter for biopotential acquisition systems

Presented is a novel powerline notch filter embeddable into a chopper-stabilised instrumentation amplifier for biopotential measurements. The frequency-translation property of the chopper enables the powerline notching to be indirectly implemented by two resonant zeros around the chopper frequency, resulting in substantial silicon area savings. Transistor-level implementation in 90 nm CMOS using a pseudo-LC circuit topology with Q-enhancement demonstrates 50 to 60 Hz frequency tunability, 25/41 dB powerline rejection at 5/30 Hz bandwidth, and 1000 relaxation of time constant under a 4 kHz chopper frequency.