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Abstract

An improved pulse oximeter incorporating an innovative method for exposing a patient's extremity to electromagnetic radiation of two wavelengths, e.g., a red wavelength and an IR wavelength, and detecting the absorbance of the extremity at each of the wavelengths, said method comprising the steps of: (a) generating overlapping first and second pulse trains of electromagnetic radiation having first and second wavelengths and having the same frequency but differing in phase by 90 degrees; (b) exposing the extremity to the first and second pulses; (c) producing an electrical signal corresponding to the electromagnetic radiation intensity of both the first and second pulses added together; (d) amplifying said electrical signal using a tuned amplifier; and (e) demodulating said electrical signal using the first pulse and second pulse, independently, as reference signals. In an alternate embodiment of the invention, improved rejection of noise is provided by using pseudo random sequences for the LED drives and the demodulator reference signals.

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First Claim