ECG power line interference removal using combination of FFT and adaptive non-linear noise estimator

Modern ECG instruments have a very high common mode rejection ratio to reduce power-line interference noise as much as possible. Nevertheless, the residual power-line noise should be eliminated. Due to the fact that, the central frequency of power-line may alters about ±1Hz and the desired signals around the central frequency should not be attenuated, applying the ideal notch filter with a fixed frequency or a band stop filter is not practical. Benefitting from the powerful microcontroller STM32F4 in a new brand of Electrocardiograph instrument “Araz630”, we present a low cost efficient method of powerline noise removal. This method includes an FFT-based algorithm to find the center frequency of power-line and then subtracting the noise estimated by adaptive non-linear algorithm. In our implementation, we achieve between 30 to 35 dB of cancellation of the fundamental power-line noise component and the central frequency is obtained by the resolution of 0.1 Hz.