Efficient IIR notch filter design using Minimax optimization for 50Hz noise suppression in ECG

Quality of Electrocardiogram (ECG) signal is very important for patient health diagnostics. ECG consists of frequencies ranging from 0.01 - 300Hz, while being a very small magnitude signal. ECG usually gets corrupted by the 50Hz power line interference (PLI). Thus, filtering out the PLI is a necessary task for the right diagnostics. In this work a second order efficient digital infinite impulse response (IIR) notch filter is designed to suppress PLI. For this task, Minimax optimization technique has been utilized to minimize the root mean square error (RMSE) defined as the difference of magnitude response of ideal and proposed IIR notch filter designs. The optimization process was able to set pole position close to the unit circle and the pass band gain is so chosen so as to have symmetrical performance resulting in attenuation at 50Hz notch of -260dB, a gain of 0.995 and -3dB bandwidth of 2.375Hz. The performance of the designed filter has been investigated theoretically as well as validated experimentally on a contaminated ECG signal and a pure sinusoid signal of 50Hz on field programmable gate array (FPGA) in the LabVIEW environment. In simulation, a power spectral density (PSD) of -30dB has been achieved for the simulated ECG signal originally having 4dB PSD at 50Hz and an attenuation of -30dB in PSD has been obtained for a pure sinusoidal signal. The designed filter was also implemented on FPGA a PSD of -26dB was obtained for ECG at 50Hz and -26dB for sinusoidal signal, respectively. Based on these studies it can be concluded that the proposed Minimax based notch filter design is an efficient one.