Patent ID: 8145287

Claim:
A method to obtain physiological data relating to a physiological parameter correlated with a measured constituent without knowing precise operating wavelengths of one or more light emitting devices in an oximeter sensor, the method comprising: driving a first light emitting device with a first drive current to generate a first light energy having a first wavelength; transmitting the first light energy through a medium under test to result in a first attenuated light energy; driving the first light emitting device with a second drive current to generate a second light energy having a second wavelength, wherein the second drive current has a different current level than the first drive current, the first wavelength and the second wavelength fall within a first predetermined range of operating wavelengths, and a difference between the first wavelength and the second wavelength is approximately equal to a preselected wavelength shift; transmitting the second light energy through the medium under test to result in a second attenuated light energy; driving a second light emitting device with a third drive current to generate a third light energy having a third wavelength, wherein the third wavelength falls within a second predetermined range of operating wavelengths and is distinct from the first wavelength and the second wavelength; transmitting the third light energy through the medium under test to result in a third attenuated light energy; and calculating the physiological parameter based on the first attenuated light energy, the second attenuated light energy, the third attenuated light energy, and the preselected wavelength shift, wherein the measured constituent has a known change in extinction coefficient corresponding with the preselected wavelength shift.