Adjustable 60Hz noise reduction by a notch filter for ECG signals

After the analog ECG signal is transferred into digital format, the digital filter can be used to suppress the 60 Hz embedded noise. In this paper, we propose the use of finite impulse response filters with a linear phase property to obtain the noise reduction without introducing the phase distortion. In our design, we use the notch filter with a pole/zero canceling method, the comb notch filter with a pole/zero canceling method and the equiripple notch filter with the usage of the Parks-McClellan algorithm. By the comparison of the transition bandwidth (Δω), stopband attenuation gain (Astop) of these filters, we can learn the frequency response of these filters. Furthermore, we use the mean square error (MSE) to estimate the effect of the digital filters in order to reduce the embedded 60 Hz noise. We compute the mean square error with respect to the order, N, of these filters and plot the relationship of MSE and N. In addition, we find the relationship of the CPU time and N, and we also learn that the CPU time is in proportion to the order, N, of the filters. According to the relations among N, MSE and CPU time, we can find that the advantages and disadvantages of the proposed filters and then choose the best filter for the corresponding conditions.