SIGNAL DEMODULATION

1 . A system, comprising:

a filter configured to receive a signal from a physiological sensor, wherein the signal comprises a first signal component and a second signal component comprising an interference component, and wherein the filter is configured to output a filtered signal;

an analog-to-digital converter configured to receive the filtered signal and sample the filtered signal in periodic intervals to generate a sampled filtered signal, wherein each periodic interval comprises n samples; and

a processor configured to:

receive the sampled filtered signal;

solve a matrix equation representing the sampled filtered signal for the first signal component, wherein the matrix equation comprises a signal vector comprising the first and second components and a matrix comprising weighted coefficients; and

determine a physiological parameter based on the first signal component and not the second signal component.

2 . The system of claim 1 , wherein the processor is configured to determine the interference component by a linear approximation between a first and last sample of each periodic interval.

3 . The system of claim 1 , wherein the filter comprises a variable filter and wherein the processor is configured to determine an inverse of the matrix of coefficients during a start-up phase of the system

4 . The system of claim 1 , wherein the filter comprises a constant filter and wherein the processor is configured to determine an inverse of matrix of coefficients.

5 . The system of claim 1 , wherein the filter comprises an adaptive filter and wherein the processor is configured to determine an inverse of the matrix of coefficients after each adaptation of the adaptive filter.

6 . The system of claim 1 , wherein the physiological sensor comprises a pulse oximetry sensor.

7 . The system of claim 1 , wherein the second signal component comprises an ambient light signal component.

8 . The system of claim 7 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

9 . The system of claim 1 , wherein the second signal component comprises cable transient components.

10 . The system of claim 9 , wherein the weighted coefficients of the matrix equation for the cable transients are determined by a transfer function of the filter and a sample position within a periodic interval

11 . The system of claim 1 , wherein the first signal component comprises a red signal component.

12 . The system of claim 1 , wherein the first signal component comprises an infrared signal component and a red signal component.

13 . The system of claim 1 , wherein the red signal component and the IR signal component are timely separated within each periodic interval and the red signal component and the IR signal component each comprise a predetermined signal length having an on and off transient.

14 . A method, comprising:

receiving a composite signal comprising a red component, an infrared component, and at least one interfering signal component;

filtering the composite signal with a filter having a transfer function H(s);

sampling the filtered composite signal with an analog to digital converter in periodic intervals wherein each periodic interval comprises n samples; and

using a processor:

solving a matrix equation representing the composite signal for the red component and the infrared component, wherein the matrix equation comprises a signal vector comprising the red component, the infrared component, and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein weighted coefficients for the at least one interfering signal component are based on an impulse response and a magnitude of an impulse;

generating an output based on the red component and the infrared component.

15 . The method of claim 14 , wherein the red component and the infrared component are represented by an impulse response at a periodic interval multiplied by a measured current.

16 . The method of claim 14 , wherein the interfering signal component comprises an ambient light signal component and cable transients.

17 . The method of claim 16 , wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval.

18 . A system, comprising:

a sensor comprising one or more light emitters and a detector configured to detect light emitted by the one or more light emitter and generate a signal, wherein the signal comprises a primary signal component and at least one of an ambient light component or a cable cross-talk component;

a patient monitor comprising:

a filter configured to receive the signal and outputting a filtered signal;

an analog-to-digital converter configured to receive the filtered signal and sample the filtered composite signal in periodic intervals wherein each periodic interval comprises n samples;

a signal processor configured to:

receive the sampled filtered signal;

solve a matrix equation for the primary signal component, wherein the matrix equation comprises a signal vector comprising the primary signal component and at least one of the ambient signal component or the cable cross-talk component and a matrix comprising weighted coefficients; and

determine a physiological parameter based at least in part on the primary signal component.

19 . The system of claim 18 , wherein the at least one of an ambient light component or a cable cross-talk component is approximated by a linear approximation between a first and last sample of each periodic interval.

20 . The system of claim 18 , wherein n is determined based on an accuracy of the physiological parameter.