Photoplethysmography (PPG) device and the method thereof

A method for measuring arterial oxygen saturation (SpO2), the method comprising:

• in a light detecting step, detecting red and infrared lights from a light detector;
• in an A/D conversion step, converting the detected signals of the light detecting step into digital signals;
• in a preprocessing step, removing noises from the digital signals of the A/D conversion step and then performing an innovation process, to increase independence between a measured Photoplethysmography (PPG) signal and motion artifact noise;
• in a centering process step, subtracting an average value from output signals from the preprocessing step;
• in a whitening process step, obtaining a whitening matrix by calculating covariance from output signals from the centering process, and by calculating eigen value and eigen matrix of the covariance;
• in a W matrix calculating step, calculating a demixing matrix W by generating a new vector V using the whitening matrix and the output signals from the centering process, by generating an arbitrary 2x2 matrix W, and by applying the V and W to a non-linear function w+, where w+=w−E{vg(wTv)}−E{g′(wTv)}w, where g is a Gaussian function;
• in a A matrix calculating step, calculating a mixing matrix A by calculating an inverse matrix of output signals from the W matrix calculating step;
• and
• in a data restoring step, restoring data using output signals from the A matrix calculating step and output signals from the centering process step.