US Patent 7336982 Photoplethysmography (PPG) device and the method thereof

A method of measuring Photoplethysmography (PPG) signals may comprise detecting dual wavelength illumination from a light detector so as to provide detected signals, converting the detected signals into digital signals so as to provide digital signals, reducing noises from the digital signals and increasing independency between the digital signals so as to provide preprocessed signals, subtracting the average value from the preprocessed signals so as to provide adjusted signals, obtaining whitening matrix based on covariance, eigen value, and eigen matrix obtained from the adjusted signals, and restoring data using the whitening matrix.