ゲート動作アバランシェフォトダイオードを用いた高感度反射型パルスオキシメータ

概要

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We propose a reflection-type pulse oximeter that employs two pairs of a light-emitting diode (LED) and a gated avalanche photodiode (APD). One LED radiates a red line with an emission wavelength of 635 nm and the other a near-infrared line with 945 nm. These are driven with a pulse current at frequency f (=10 kHz). Superposition of a transistor-transistor-logic (TTL) gate pulse on a direct-current (dc) bias, which is set so as not to exceed the breakdown voltage of each APD, makes the APD work in a gain-enhanced operation mode. Each APD is gated at frequency 2f (=20 kHz), and the signal output is fed into a laboratory-made lock-in amplifier that works synchronously with the pulse modulation signal of each LED at frequency f (=10 kHz). A combination of the gated APD and lock-in like signal detection scheme is useful for the reflection-type pulse oximeter owing to the capability of detecting a weak signal against a large background light.
2005-12-10