A Sensitive Reflection-type Pulse Oximeter Using a Gated Avalanche Photodiode

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  • MIYATA Tsuyoshi
    Graduate School of Engineering Science, Osaka University
  • IWATA Tetsuo
    Department of Mechanical Engineering, Faculty of Engineering, The University of Tokushima
  • ARAKI Tsutomu
    Graduate School of Engineering Science, Osaka University

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Other Title
  • 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
  • ゲート ドウサ アバランシェフォトダイオード オ モチイタ コウカンド ハンシャガタ パルスオキシメータ

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Abstract

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 ƒ (= 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 2ƒ (= 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 ƒ (= 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.

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