Method and apparatus for correction of microbolometer output

• US 20010040216A1
• Filed: 03/15/2001
• Published: 11/15/2001
• Est. Priority Date: 03/17/2000
• Status: Active Grant

• Current Assignee: Infrared Components Corporation
• Original Assignee: Infrared Components Corporation
• Inventors: Balick, Steven M., Knauth, Jonathan P.
• Granted Patent: US 6,610,984 B2
• Time in Patent Office: Days
• US Class Current: 250/352
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: H04N 25/21 for transforming thermal infrared radiation into image signals
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A method and apparatus for correction of temperature-induced variations in the analog output characteristics of a microbolometer detector in an infrared detecting focal plane array utilizing electronic means to correct for the temperature variation of the individual microbolometer detector. The electronic circuitry and associated software necessary for implementation is also described.

Claims

1. A method of correcting the output of a microbolometer detector system, said method comprising:

providing a microbolometer detector system for operation in an ambient temperature range, said microbolometer detector system further comprising at least one microbolometer detector, and an apparatus for reducing thermal noise;

providing a temperature stabilization system for correcting the temperature variation of the microbolometer detector;

providing an electronic system for conditioning the output of the microbolometer detector; and

applying a correction factor to the output signal of the microbolometer detector.

2. The method of

claim 1

, wherein the ambient temperature range is between approximately −

10°

C. and +50°

C.

3. The method of

claim 1

, wherein the apparatus for reducing thermal noise is selected from the group consisting of a lens, a dewar window, and a cold shield.

4. The method of

claim 1

, wherein the electronic system:

responds to variations in a radiant flux signal from a source;

modulates the sensitivity of the microbolometer detector to the variations in the radiant flux signal;

converts the output from the microbolometer detector from an analog signal to a digital signal using an analog-to-digital converter; and

limits the output from the microbolometer detector so that the microbolometer detector output remains within an input sensitivity range of the analog-to-digital converter.

5. The method of

claim 3

, wherein applying the correction factor to the output signal of the microbolometer detector decreases effects of temperature variations in the lens, dewar window, or cold shield.

6. The method of

claim 1

, wherein the electronic system performs an algorithm to calculate a corrected offset value based on the difference between an individual microbolometer detector temperature and a baseline temperature.

7. The method of

claim 6

, wherein the baseline temperature is approximately at the center of the operational temperature range of the microbolometer detector.

8. The method of

claim 6

, wherein an average offset difference function vs. detector temperature is calculated from a plurality of offset values corresponding to different microbolometer detectors.

9. The method of

claim 8

, wherein the average offset difference function is a polynomial expression.

10. The method of

claim 9

, wherein the average offset difference function is a polynomial expression determined via empirical curve fitting of calibration data for the plurality of microbolometer detectors.

11. The method of

claim 10

, wherein thermal noise is substantially removed by calculating a new offset value, said new offset value the result of algebraically combining the offset difference function with a pixel offset value for each microbolometer detector.

12. The method of

claim 11

, wherein the offset difference function is calculated based on the average of a plurality of different mic:

robolometer detectors.

13. The method of

claim 12

, wherein the pixel offset values are stored in a memory.

14. The method of

claim 10

, wherein a pixel variance correction factor is determined by calculating the ratio of the offset difference function, based on microbolometer detector data, and an actual difference between the pixel offset at a calibration temperature and the pixel offset at a second temperature.

15. The method of

claim 14

, wherein the pixel variance correction factor is applied to the plurality of microbolometer detectors on a real time basis.

16. A method of correcting the output of a microbolometer detector system, said method comprising:

providing a microbolometer detector system for operation in an ambient temperature range, said microbolometer detector system further comprising at least one microbolometer detector, and an apparatus for reducing thermal noise;

providing a temperature stabilization system for correcting the temperature variation of the microbolometer detector;

providing an electronic system for conditioning the output of the microbolometer detector;

providing a system for varying the responsivity of the microbolometer;

applying a correction factor to the output signal of the microbolometer detector.

17. The method of

claim 16

, wherein the apparatus for reducing thermal noise is selected from the group of system components consisting of a lens, a dewar window, and a cold shield.

18. The method of

claim 16

, wherein varying the method of varying the responsivity is selected from the group consisting of:

varying the applied bias voltage, varying the sampling frequency, or varying the degree of mechanical vignetting applied to the microbolometer detector.

19. The method of

claim 18

, wherein an offset value is calculated by performing a series of calibration steps:

adjusting the sampling time, bias voltage, or degree of mechanical vignetting;

recording the resulting analog offset values which satisfy the requirement that the output of the microbolometer detector be well matched to the input sensitivity range of a analog-to-digital converter; and

curve fitting the results.

20. The method of

claim 19

, further comprising the step of applying an analog offset correction factor.

21. The method of

claim 19

, further compensating for variations in the temperature of system components, said steps comprising:

providing temperature sensors operationally connected to said system components;

monitoring said temperature sensors;

correlating system component temperatures with an analog offset voltage required to bring said microbolometer detector output to the approximate center of the input sensitivity range of the analog-to-digital converter;

curve fitting the correlated system component temperatures and the analog offset voltages; and

producing at least one mathematical function of analog offset voltage vs. system component temperature.

22. An apparatus for correction of a microbolometer detector output, said apparatus comprising:

at least one microbolometer detector;

a thermal noise reduction system operationally connected to said at least one microbolometer detector;

an electrical reference circuit connected to said at least one microbolometer detector;

an output from said electrical reference circuit connected to an input of a signal conditioning circuit; and

an output from said signal conditioning circuit connected to a display device.

23. The apparatus of

claim 22

, wherein the signal conditioning circuit further comprises:

a differential amplifier;

a first reference source;

a signal processor;

an output from said electrical reference circuit connected to a first input of said differential amplifier;

an output from said first reference source connected to a second input of said differential amplifier; and

an output from said signal processor connected to said first reference source, wherein the output of the first reference source is determined by the signal processor.

24. The apparatus of

claim 23

, further including:

a temperature sensor operationally connected to said microbolometer;

a second reference source operationally connected to said temperature sensor;

an analog-to-digital converter operationally connected to said temperature sensor, said second reference source, and to said signal processor.

25. The apparatus of

claim 23

, wherein the first reference source is a voltage source.

26. The apparatus of

claim 25

, wherein the voltage source is a digital-to-analog converter.

27. The apparatus of

claim 22

, wherein the signal conditioning circuit contains an algorithm to calculate a corrected offset value based on the difference between an individual microbolometer detector temperature and a baseline temperature.

28. The apparatus of

claim 27

, wherein the baseline temperature is approximately at the center of the operational temperature range of the microbolometer detector.