| 摘要 |
PURPOSE: To realize a high sensitivity measurement by passing a signal through a filter which exhibits blocking characteristics for the frequency range of spurious signal and exhibits transmission characteristics for the frequency range of information signal and processing the filter signal to block the spurious signal. CONSTITUTION: For example, a pickup 2 is provided with light emitting elements 3a-3c emitting a light beam 6 sequentially with wavelengthλ1 -λ3 , respectively. A light beam 9 reflected on a hemoglobin 8 impinges on a light receiving element 4 together with a spurious signal caused by an ambient light 17. Outputs U1 -U3 from the element 4 are delivered through a high-pass filter 14 to an evaluation circuit 16. A function representative of deviation of the frequency response of a filter 14 from ideal transmission characteristics is determined in the frequency range of information signal. Subsequently, an inverted function thereof is determined and the output from filter 14 is weighted according to the inverted function. Since the output signal from filter 14 is subjected to inverted electrical processing, distortion due to the filter 14 is eliminated completely.
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