Patent ID: 8126528

Claim:
In a signal processor, a method of determining a measurement value for a characteristic of arterial blood, the method comprising: receiving a first time-domain signal that is indicative of light of a first wavelength that has been attenuated by body tissue carrying arterial blood; receiving a second time-domain signal that is indicative of light of a second wavelength that has been attenuated by the body tissue carrying arterial blood; electronically transforming the first and second time-domain signals into respective first and second frequency-domain signals; electronically determining a comparison value for each of a plurality of non-zero frequency components of the first and second frequency-domain signals, each comparison value comprising a comparison of the amount of a frequency component in the first frequency-domain signal versus the amount of that frequency component in the second frequency-domain signal; electronically selecting a frequency component that exhibits physiological characteristics of arterial blood using, at least in part, the corresponding comparison value; and electronically determining the measurement value for the characteristic of arterial blood using the selected frequency component.