Method and apparatus for demodulating signals in a pulse oximetry system

A method of determining an indication of a physiological parameter by demodulating a composite output signal from a detector of a noninvasive optical sensor, the method comprising:

• activating at least one light source to cause a first emission at a first wavelength;
• activating the at least one light source to cause a second emission at a second wavelength at least once before a reactivation of the at least one light source;
• wherein activating includes inactivating the at least one light source to cause no signal emissions;
• detecting the composite output signal indicative of an attenuation by said body tissue of said first and second emissions;
• demodulating said composite output signal into a first intensity signal responsive to said attenuation of said first emission, into a second intensity signal responsive to said attenuation of said second emission and into a third signal representative of a non-physiological portion of the output signal, wherein said demodulation is based at least in part on the inactivation;
• and
• determining an indication of a physiological parameter of said body tissue based on one or more of said first and second intensity signals.

A system for determining an indication of a physiological parameter by demodulating a composite output signal from a detector of a noninvasive oximetry optical sensor, the system comprising:

• an input configured to receive a composite signal indicative of an attenuation by body tissue of a first and second emission, said composite signal including at least one inactivation of said first and second emissions;
• and
• a processor configured to demodulate said composite signal into a first intensity signal responsive to said attenuation of said first emission and into a second intensity signal responsive to said attenuation of said second emission and into a third signal representative of a non-physiological portion of the output signal, wherein said demodulation is based at least in part on the inactivation;
• wherein said processor is further configured to determine an indication of a physiological parameter of said body tissue based on one or more of said first and second intensity signals.

A method of determining an indication of a physiological parameter by demodulating a composite output signal from a detector of a noninvasive optical sensor, the method comprising:

• receiving a composite output signal indicative of an attenuation by a body tissue of a first and second emission of a light source, said composite signal including at least one inactivation of said first and second emissions;
• demodulating said composite output signal into a first intensity signal responsive to said attenuation of said first emission, into a second intensity signal responsive to said attenuation of said second emission and into a third signal representative of a non-physiological portion of the output signal, wherein said demodulation is based at least in part on the inactivation;
• and
• determining an indication of a physiological parameter of said body tissue based on one or more of said first and second intensity signals.