Figure 9 shows the frequency spectrum of the ECG signal
without any implementation of digital filter in MATLAB. In
this figure, magnitude for 50Hz is 0.001233 and that is for
common-mode voltage produced by the ac mains of 50 Hz
frequency with line voltage 220V. Due to this ECG signal in
figure 8 is contaminated with power line interference (50Hz).
Though, in this system signal conditioning and signal
transmitting circuit is isolated from ac mains there exist a small
amount of power line interference. This is because of the
capacitance between power lines in the wall, floor and nearby
equipment couples current into the patient, wires and system
equipment.
For filtering first, a 4th order butterworth band pass filter
was implemented with a lower and higher cutoff frequency of
.033Hz and 120Hz. After that a 4th order elliptic band stop