Signal demodulation

Abstract

A method for processing an analog composite signal in a system has the steps of receiving a composite signal with 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 has n samples; forming a matrix equation representing the composite signal wherein the matrix equation has a signal vector with the at least first one signal component and the at least one interfering signal component and a matrix comprising weighted coefficients; solving the matrix equation to determine the at least one signal component; outputting the at least one signal component.

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.