Apparatus and method for medical monitoring, in particular pulse oximeter

Abstract

A method for measuring medical parameters of a patient by radiation of electromagnetic waves into a sample and for measurement and subsequent analysis of the electromagnetic waves which have passed through the sample, the following steps are carried out. First and second modulation signals are generated having equal frequencies and a first phase difference of substantially 90.degree.. Irradiating a first electromagnetic wave of a first wavelength into the sample, under control of the first modulation signal. Irradiating the sample with a second electromagnetic wave of a second wavelength, under control of the second modulation signal. Receiving electromagnetic waves of both wavelengths which have passed through the sample and demodulating the received signals by multiplying the same with a first sinusoidal demodulation signal and with a second sinusoidal demodulation signal having the first phase difference with respect to the first sinusoidal signal, the first and second sinusoidal demodulation signals having the same frequency as the first and second modulation signals, such as to generate a first and a second demodulated signal. The first and the second sinusoidal demodulated signals are set so as to have a phase difference relative to the first and second modulation signals corresponding to a system phase shift.