| 摘要 |
PROBLEM TO BE SOLVED: To precisely measure oxygen saturation in a pulse oximeter for measuring arterial blood oxygen saturation in a noninvasive manner by utilizing a difference in light absorption characteristics between two wavelengths of red light and infrared light in a living body. SOLUTION: A current/voltage conversion circuit 5 converts a current signal from a light receiving element 4 to a voltage signal by using Vref1 as a reference and amplifies it, and an amplifying circuit 6 in a second step further amplifies the voltage output. An A/D conversion circuit 7 performs A/D conversion, and an arithmetic device (CPU) 8 takes in the outcome and calculates the arterial blood oxygen saturation. The arithmetic device 8 creates the Vref1 of a level which has an eliminated pulse (AC) portion of a digital signal and corresponds to non-varied (DC) portion while considering the reference voltage Vref1 variable and imparts to the current/voltage conversion circuit 5. The current/voltage conversion circuit 5 converts the pulse (AC) portion obtained by subtracting the non-varied (DC) portion from the input current signal to a voltage with a large gain of an unsaturated level. Therefore, when the pulse is small with a small alternate current component, the oxygen saturation is precisely measured. COPYRIGHT: (C)2009,JPO&INPIT
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