Signal demodulation

1. A method for processing an analog composite signal in a system, the method comprising the steps of:

receiving a composite signal comprising at least one first signal 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 in periodic intervals wherein each periodic interval comprises n samples;

forming a matrix equation representing the composite signal wherein the matrix equation comprises a signal vector comprising the at least one first signal component and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein the weighted coefficients for a transient interfering signal component are determined by the transfer function and a sample position within a periodic interval;

solving the matrix equation to determine the at least one signal component;

outputting the at least one signal component.

2. The method according to claim 1 , wherein an interfering signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

3. The method according to claim 1 , wherein the system is an oximeter system comprising an oximeter sensor generating a Red signal component and an Infrared (IR) signal component as signal components and wherein an ambient light signal component and cable transients are interfering signal components.

4. The method according to claim 3 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

5. The method according to claim 3 , wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval.

6. The method according to claim 3 , 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.

7. The method according to claim 6 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval and the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval, and wherein a coefficient matrix comprises first and second coefficients for the linear approximation, switch on and switch off coefficients for the cable transients, a Red coefficient, and an IR coefficient.

8. A system for processing an analog composite signal comprising at least one first signal component and at least one interfering signal component, the system comprising:

a filter having a transfer function H(s) receiving the composite signal and outputting a filtered composite signal;

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

a signal processor receiving the sampled filtered composite signal, wherein the signal processor forms a matrix equation representing the composite signal wherein the matrix equation comprises a signal vector comprising the at least one first signal component and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein the weighted coefficients for a transient interfering signal component are determined by the transfer function and a sample position within a periodic interval, wherein the signal processor is furthermore operable to solve the matrix equation to calculate the at least one signal component and to output the at least one signal component.

9. The system according to claim 8 , wherein an interfering signal is approximated by a linear approximation between a first and last sample of each periodic interval.

10. The system according to claim 8 , wherein the system is an oximeter system comprising an oximeter sensor generating a Red signal component and an Infrared (IR) signal component as signal components and wherein an ambient light signal component and cable transients are interfering signal components.

11. The system according to claim 10 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

12. The system according to claim 10 , wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval.

13. The system according to claim 10 , 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. The system according to claim 13 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval and the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval, and wherein a coefficient matrix comprises first and second coefficients for the linear approximation, switch on and switch off coefficients for the cable transients, a Red coefficient, and an IR coefficient.

15. An oximeter system comprising:

an oximeter sensor generating an output signal with a Red signal component and an Infrared (IR) signal component which are timely separated within a periodic interval wherein the Red signal component and the IR signal component each comprise a predetermined signal length having an on and off transient,

a filter having a transfer function H(s) receiving a composite signal consisting of the oximeter sensor output signal and at least one interfering signal component, wherein the filter outputs a filtered composite signal;

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

a signal processor receiving the sampled filtered composite signal, wherein the signal processor forms a matrix equation representing the composite signal wherein the matrix equation comprises a signal vector comprising the Red and IR signal components and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein an ambient light signal component and cable transients are interfering signal components and wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval, wherein the signal processor is furthermore operable to solve the matrix equation to calculate the Red and IR signal components and to output the Red and IR signal components.

16. The oximeter system according to claim 15 , wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

17. The oximeter system according to claim 15 , wherein the ambient light component is approximated by a linear approximation between a first and last sample of each periodic interval and the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval, and wherein a coefficient matrix comprises first and second coefficients for the linear approximation, switch on and switch off coefficients for the cable transients, a Red coefficient, and an IR coefficient.

18. A method for processing an analog composite signal in an oximeter system, the method comprising the steps of:

receiving a composite signal comprising at Red signal component and an infrared (IR) signal component from an oximeter sensor 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 in periodic intervals wherein each periodic interval comprises n samples;

forming a matrix equation representing the system wherein the matrix equation comprises a signal vector comprising the Red and IR signal component and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein an ambient light signal component and cable transients are interfering signal components, wherein the ambient light is approximated by a linear approximation between a first and last sample of each periodic interval and wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval;

solving the matrix equation to calculate the Red and IR signal components;

outputting the Red and IR signal components.

19. The method according to claim 18 , 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.

20. The method according to claim 19 , wherein the ambient light is approximated by a linear approximation between a first and last sample of each periodic interval and the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval, and wherein a coefficient matrix comprises first and second coefficients for the linear approximation, switch on and switch off coefficients for the cable transients, a Red coefficient, and an IR coefficient.