Patent ID: 8755856

Claim:
In a signal processor, a method of determining a measurement of a characteristic of arterial blood, the method comprising: transforming first and second time-domain signals into respective first and second frequency-domain signals, the first and second time-domain signals being indicative of light that has been attenuated by body tissue carrying arterial blood; determining one or more values for a plurality of non-zero frequency components of the first and second frequency-domain signals that are indicative of the strength of one or more frequency components of the first frequency-domain signal versus the strength of one or more corresponding frequency components in the second frequency-domain signal; determining one or more phase differences between respective frequency components of the first and second frequency-domain signals: selecting one or more frequency components that exhibit physiological characteristics of arterial blood based, at least in part, on the corresponding one or more values and the one or more phase differences; and determining the measurement for the characteristic of arterial blood using the selected one or more frequency components.