Implanted sensor processing system and method for processing implanted sensor output

Abstract

A quantitative measurement system includes an external unit and an internal unit are provided for obtaining quantitative analyte measurements, such as within the body. In one example of an application of the system, the internal unit would be implanted either subcutaneously or otherwise within the body of a subject. The internal unit contains optoelectronics circuitry, a component of which may be comprised of a fluorescence sensing device. The optoelectronics circuitry obtains quantitative measurement information and modifies a load as a function of the obtained information. The load in turn varies the amount of current through coil, which is coupled to a coil of the external unit. A demodulator detects the current variations induced in the external coil by the internal coil coupled thereto, and applies the detected signal to processing circuitry, such as a pulse counter and computer interface, for processing the signal into computer-readable format for inputting to a computer.

1 . In a system comprising (a) an internal sensor unit having a circuit and (b) an external sensor unit, a method for determining the concentration of an analyte, comprising:
 using the external sensor unit to provide power to the internal sensor;   while the external sensor unit is providing power to the internal sensor unit,
 communicating to the external sensor unit information from which the concentration of the analyte can be determined, wherein the communicating step comprises changing an impedance of the circuit as a function of the concentration of the analyte, wherein a change in the impedance of the circuit causes a voltage in the external sensor unit to change; and 
 obtaining measurements of the voltage; and 
   generating information from the voltage measurements, wherein the information includes information from which the concentration of the analyte can be determined.   
     
     
         2 . The method of  claim 1 , wherein the communicating step consists essentially of changing the impedance of the circuit as a function of the concentration of the analyte. 
     
     
         3 . The method of  claim 2 , wherein the communicating step consists of changing the impedance of the circuit as a function of the concentration of the analyte. 
     
     
         4 . The method of  claim 1 , wherein the communicating step comprises changing a resistance of the circuit as a function of the concentration of the analyte. 
     
     
         5 . The method of  claim 1 , wherein the internal sensor unit comprises a signal channel detector to detect the presence or concentration of the analyte and a reference channel detector not responsive to the analyte, and the information communicated to the external unit comprises information that is a function of the output of the signal detector and the output of the reference channel. 
     
     
         6 . The method of  claim 5 , further comprising generating a signal having a duty cycle, wherein the duty cycle of the signal is a function of the output of the signal channel detector and the output of the reference channel detector. 
     
     
         7 . The method of  claim 6 , comprising using the signal to change the impedance of the circuit. 
     
     
         8 . Apparatus for retrieving information from a sensor device, comprising:
 an internal sensor unit for taking quantitative analyte measurements, including a first coil forming part of a power supply for said sensor unit, a load coupled to said first coil, and a sensor circuit for modifying said load in accordance with sensor measurement information obtained by said sensor circuit, said sensor circuit including a signal channel detector responsive to analyte measurement information, and a reference channel detector responsive to reference measurement information, outputs of said signal channel detector and said reference channel detector being combined in said sensor information for modifying said load, wherein said signal channel detector is configured to produce an output determinative of a positive transition time of said load modification, and said reference channel detector is configured to produce an output determinative of a negative transition time of said load modification;   an external unit including a second coil which is mutually inductively coupled to said first coil upon said second coil being placed within a predetermined proximal distance from said first coil, an oscillator for driving said second coil to induce a charging current in said first coil, and a detector for detecting variations in a load on said second coil induced by changes to said load in said internal sensor unit and for providing information signals corresponding to said load changes; and   a processor for receiving and processing said information signals;   wherein said reference channel detector is configured to produce an output determinative of a positive transition time of said load modification, and said signal channel detector is configured to produce an output determinative of a negative transition time of said load modification.   
     
     
         9 . A sensor system, comprising:
 an internal unit, including:
 a tank circuit comprising a first coil and a capacitor, and 
 a optoelectronics circuitry coupled to the tank circuit, said optoelectronics circuitry being configured to (1) obtain quantitative measurement information and (2) change the impedance of a circuit connected to the tank circuit as a function of the obtained quantitative measurement information; and 
   an external unit, including:
 a second coil, 
 an oscillator coupled to the second coil, and 
 a detector coupled to the second coil, said detector being configured to detect a change in said impedance when the second coil is inductively coupled to the first coil. 
   
     
     
         10 . The sensor system of  claim 9 , wherein the optoelectronics circuitry includes a light source, a signal channel photodetector and a reference channel photodetector, said first and second photodetectors being arranged in a back-to-back manner. 
     
     
         11 . The sensor system of  claim 10 , wherein the optoelectronics circuitry further includes a comparator, wherein an input terminal of the comparator is connected to a terminal of one of said photodetectors. 
     
     
         12 . The sensor system of  claim 11 , wherein the optoelectronics circuitry is configured to output a signal having a duty cycle that is indicative of changes between incident light on the signal channel photodetector and incident light on the reference channel photodetector. 
     
     
         13 . The sensor of  claim 12 , wherein a resistor is electrically connected between an output terminal of the comparator and a terminal of the first coil.