Ambient light compensation circuit for analyte measurement systems

Patent metadata

Field	Value
Publication number	US-9404794-B2
Application number	US-201313780518-A
Country	US
Kind code	B2
Filing date	Feb 28, 2013
Priority date	Feb 28, 2013
Publication date	Aug 2, 2016
Grant date	Aug 2, 2016

Abstract

A blood analyte measurement system is configured to receive a test strip. An LED proximate to the test strip is used to illuminate the test strip and, in conjunction with a photodiode, to determine its type. A compensation circuit of the measurement system insures that ambient light does not cause interference with the LED illumination to prevent saturation of the photodiode.

First claim

What is claimed is:

1. An ambient light compensation circuit comprising:
a first gain stage comprising:
a voltage source;
a power supply;
a photodiode connected to the voltage source;
a first operational amplifier connected to the photodiode and to the power supply, the first operational amplifier having a first gain stage output terminal;
a first voltage divider connected to the voltage source and the first operational amplifier for providing a first reference voltage to the first operational amplifier, the voltage divider comprising a first pair of resistors; and

a coupling capacitor coupled in series to the first gain stage output terminal and to a second gain stage, the coupling capacitor for transmitting a voltage pulse from the first gain stage output terminal to the second gain stage,

wherein the second gain stage comprises:
a second operational amplifier connected to the coupling capacitor through a coupling resistor and to the power supply, the second operational amplifier having a compensation circuit output terminal;
a second voltage divider connected to the voltage source and to the second operational amplifier for providing a second reference voltage to the second operational amplifier, the second voltage divider comprising a second pair of resistors; and
wherein the compensation circuit output terminal is connected to the coupling resistor through a second stage gain control resistor for compensating a DC voltage of the coupling capacitor, the DC voltage generated by ambient light impacting the photodiode.

2. The ambient light compensation circuit of claim 1 , wherein the first gain stage further comprises a first roll off capacitor and a first stage gain control resistor both connected to the first gain stage output terminal and to the photodiode, and a grounded decoupling capacitor connected to the first operational amplifier.

3. The ambient light compensation circuit of claim 1 , wherein the first gain stage further comprises a limiter diode connected to the first gain stage output terminal and to the photodiode.

4. The ambient light compensation circuit of claim 1 , wherein the voltage pulse from the first gain stage output terminal is generated by a light pulse impacting the photodiode.

5. The ambient light compensation circuit of claim 4 , wherein the second gain stage further comprises a roll off capacitor connected to the compensation circuit output terminal and to the coupling resistor, and a grounded decoupling capacitor connected to the second operational amplifier.

6. The ambient light compensation circuit of claim 1 , wherein the second gains stage further comprises an electronic switch connected to the compensation circuit output terminal and to the coupling resistor for selectively bypassing the second stage gain control resistor to compensate the DC voltage of the coupling capacitor.

7. An analyte meter comprising:
a processing unit
a test strip port for receiving a test strip inserted therein;
an LED proximate to the test strip port for illuminating the test strip with a light pulse when the LED is activated, the LED electrically connected to the processing unit for receiving an activation signal therefrom;
a photodiode for detecting light from the test strip;
a compensation circuit connected to the photodiode and the processing unit, and configured to detect a level of ambient light impacting the photodiode, and
a circuit for detecting that the test strip is inserted in the test strip port, and wherein the processing unit is programmed to transmit the activation signal to the LED only after the test strip is inserted in the test strip port and that the compensation circuit is in a steady state.

8. The analyte meter of claim 7 , wherein the compensation circuit comprises a capacitor configured to accumulate charge generated by the ambient light impacting the photodiode.

9. The analyte meter of claim 8 , wherein the compensation circuit comprises:
an amplifier having an input connected to the capacitor and configured for detecting the accumulated charge; and
a compensation output connected to the capacitor and to the processing unit, the amplifier further configured to compensate the accumulated charge on the capacitor through the compensation output.

10. The analyte meter of claim 9 , further comprising a circuit for detecting a voltage level of the compensation output, wherein the processing unit detects the steady state by detecting that the voltage level of the compensation output remains substantially steady for a predetermined period of time.

11. The analyte meter of claim 10 , wherein the photodiode is configured to generate an electric current upon detecting the light from the test strip, the light from the test strip generated in response to the LED illuminating the test strip with the light pulse.

12. The analyte meter of claim 11 , wherein the compensation circuit is configured to generate a voltage signal in response to the electric current, the voltage signal passing through the capacitor and through the compensation output to the processing unit.

13. The analyte meter of claim 12 , wherein the processing unit is programmed to determine a type of the test strip in response to the voltage signal.

14. A method of operating an analyte meter, the method comprising:
receiving a test strip;
monitoring a voltage level of a compensation circuit that is responsive to an ambient light intensity proximate to the analyte meter; and
analyzing the received test strip only if the voltage level has remained substantially constant for a preselected time duration.

15. The method of claim 14 , further comprising disposing a photodiode in the compensation circuit that is sensitive to the ambient light intensity.

16. The method of claim 15 , wherein the step of analyzing comprises emitting a light pulse at the test strip.

17. The method of claim 16 , further comprising disposing the photodiode in the compensation circuit such that it is sensitive to the light pulse impacting the test strip.

18. The method of claim 17 , further comprising configuring the photodiode to generate a current proportional to the combined ambient light intensity and the light pulse impacting the test strip.

19. The method of claim 18 , further comprising configuring the compensation circuit to convert the current to a voltage signal having an amplitude proportional to an amplitude of the current.

20. The method of claim 18 , further comprising configuring the compensation circuit to block a portion of the voltage signal corresponding to the ambient light intensity.

21. The method of claim 19 , further comprising configuring the compensation circuit to pass a portion of the voltage signal corresponding to the light pulse.

22. The method of claim 20 , wherein said configuring the compensation circuit to block a portion of the voltage signal and said configuring the compensation circuit to pass a portion of the voltage signal both comprise disposing a capacitor in the compensation circuit and configuring the compensation circuit to compensate charge accumulating in the capacitor from the blocked portion of the voltage signal.

23. The method of claim 21 , further comprising transmitting the portion of the voltage signal corresponding to the light pulse to a processing system for determining a type of the test strip.

Assignees

• Lifescan Scotland Ltd

Inventors

• Elder David
• Ritchie Lawrence
• Knight Paul

Classifications

• G01J1/0271

  Housings; Attachments or accessories for photometers · CPC title

• G01J1/0228

  Control of working procedures; Failure detection; Spectral bandwidth calculation · CPC title

• G01J1/4204 Primary

  with determination of ambient light (solar light G01J2001/4266) · CPC title

• G01J1/0219

  Electrical interface; User interface · CPC title

• G01J2001/0257

  portable · CPC title