A low-pass notch filter for bioelectric signals

Many bioelectric signals have relatively low-frequency content, but measurement devices are susceptible to power-line interference. The Type II Chebyshev low-pass filter can simultaneously perform the required low-pass filtering and removal of the narrowband interference. This filter has transfer-function zeros which result in zero gain (- infinity dB) at specific ´null´ frequencies. A procedure for the low-pass filter design makes the first null frequency a design parameter so that the notch can occur at the interference frequency.