Design of N-path notch filter circuit with switched-capacitor resistor

Hum noise such as power line interference is one of the critical problems in biomedical signal acquisition. Various techniques have been proposed to suppress power line interference, such as an N-path notch filter. The notch depth in the conventional N-path notch filter is limited by the number of paths. The previous 10-phase N-path notch filter circuit achieved deeper notch depth but has a problem with capacitor size. The previous circuit requires more input–output pin because the large capacitance and therefore can not be implemented on an integrated circuit. This work proposed a new N-path notch filter with a switched-capacitor resistor to enable on-chip implementation. The proposed N-path notch filter achieved deeper notch depth than previous circuits with smaller capacitors. The proposed circuit still reached notch depth deeper than 40 dB with a total capacitance of 1 nF.