Method and apparatus for demodulating signals in a pulse oximetry system

1. 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:

outputting activation signals to activate one or more light sources to cause emissions at least two different wavelengths; wherein the activation signals include at least one period of inactivation;

receiving a detected composite signal indicative of an attenuation by said body tissue of said at least two different wavelengths;

demodulating said composite signal into a first intensity signal responsive to said attenuation of at least a first of the at least two wavelengths, a second intensity signal responsive to said attenuation of at least a second of the at least two wavelengths and a third signal representative of a non-physiological portion of the composite 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.

2. The method of claim 1 , wherein demodulating further comprises using a demodulation constraint.

3. The method of claim 2 , wherein using a demodulation constraint further comprises adjusting said demodulation constraint based at least in part on the composite signal.

4. The method of claim 3 , wherein adjusting said demodulation constraint based at least in part on the composite signal further comprises using feedback.

5. 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.

6. The method of claim 5 , wherein demodulating further comprises using a demodulation constraint.

7. The method of claim 6 , wherein using a demodulation constraint further comprises adjusting said demodulation constraint based at least in part on the output signal.

8. The method of claim 7 , wherein adjusting said demodulation constraint based at least in part on the output signal further comprises using feedback.

9. 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.

10. The system of claim 9 , wherein said processor is further configured to determine a demodulation constraint and used said demodulation constraint to demodulate said composite signal.

11. The method of claim 10 , wherein said demodulation constraint is adjusted based at least in part on the output signal.

12. The method of claim 11 , wherein said demodulation constraint is adjusted using feedback.

13. 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.

14. The method of claim 13 , wherein demodulating further comprises using a demodulation constraint.

15. The method of claim 14 , wherein using a demodulation constraint comprises determining a demodulation coefficient which reduces crosstalk.

16. The method of claim 13 , wherein demodulating further comprises demodulating a predetermined number of harmonics of said first and second emissions.