Importance

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Abstract

An improved circuit for processing the received signals of a pulse oximeter includes at least first and second light-emitting diodes for transmitting light of first and second frequencies toward the finger of a user. The first diode is responsive to a first control signal for transmitting light of the first frequency. The second diode is responsive to a second control signal for transmitting light of the second frequency. Also, the first diode is responsive to a modulated control signal for transmitting a modulated light signal also of the first frequency. A photodetector is constructed to receive a first composite signal, representing the amount of light transmitted by the first diode in response to the first control signal, and a second composite signal, representing the amount of light transmitted by the second diode in response to the second control signal, wherein the first and second composite signals each include a desired signal portion and an undesired signal portion. The photodetector also receives a noise signal representing the amount of light transmitted through the finger by the first diode in response to the modulated control signal. The first and second composite signals are adaptively combined with the noise signal to provide the desired signal portion of the first and second signals, wherein the ratio of the desired signal portions represent the red to infrared ratio of the pulse oximeter. The red to infrared ratio of the pulse oximeter is combined with the second composite signal to provide the modulated control signal.

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First Claim