Pulse oximeter using a gain-modulated avalanche photodiode operated in a pseudo lock-in light detection mode

Tsuyoshi Miyata; Tetsuo Iwata; Tsutomu Araki

doi:10.1117/12.667138

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2 February 2006 Pulse oximeter using a gain-modulated avalanche photodiode operated in a pseudo lock-in light detection mode

Tsuyoshi Miyata; Tetsuo Iwata; Tsutomu Araki

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Proceedings Volume 6026, ICO20: Biomedical Optics; 60260K (2006) https://doi.org/10.1117/12.667138
Event: ICO20:Optical Devices and Instruments, 2005, Changchun, China

Abstract

We propose a reflection-type pulse oximeter, which employs two pairs of a light-emitting diode (LED) and a gated avalanche photodiode (APD). One LED is a red one with an emission wavelength λ = 635 nm and the other is a near-infrared one with that λ = 945 nm, which are both driven with a pulse mode at a 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 exceeding the breakdown voltage of each APD, makes the APD work in a gain-enhanced operation mode. Each APD is gated at a frequency 2f (=20 kHz) and its output signal is fed into a laboratory-made lock-in amplifier that works in synchronous with the pulse modulation signal of each LED at a frequency f (=10 kHz). A combination of the gated APD and the lock-in like signal detection scheme is useful for the reflection-type pulse oximeter thanks to the capability of detecting a weak signal against a large background (BG) light.

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Tsuyoshi Miyata, Tetsuo Iwata, and Tsutomu Araki "Pulse oximeter using a gain-modulated avalanche photodiode operated in a pseudo lock-in light detection mode", Proc. SPIE 6026, ICO20: Biomedical Optics, 60260K (2 February 2006); https://doi.org/10.1117/12.667138

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