Patent ID: 8376952

Claim:
A blood oxygen sensor comprising: an oscillating light generator to generate an oscillating light having an electromagnetic wavelength absorbable by a tissue of a person in an amount proportional to a volume of oxygenated blood in the tissue such that a first portion of the oscillating light exits the tissue and a second portion of the light is absorbed by the oxygenated blood; a light detector to detect a level of light near the tissue and to create a detector signal related to the detected light level, wherein the detected level includes a first detected component comprising at least some of the first portion of the oscillating light exiting the tissue and a second detected component comprising external secondary light; a bias light source to generate bias light to combine with the second detected component, wherein the bias light varies in proportion to the second detected component; a filter to attenuate at least part of the second detected component and the bias light and to pass the first detected component of the detector signal substantially un-attenuated; a memory having machine readable instructions stored therein; and a processor which, when executing the machine readable instructions, determines the volume of oxygenated blood based on the first detected component and determines circulatory characteristic relating to the person based on the volume of oxygenated blood.