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.
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