Method and apparatus for correction of microbolometer output

• US 6,630,674 B2
• Filed: 03/13/2001
• Issued: 10/07/2003
• Est. Priority Date: 03/17/2000
• Status: Expired due to Fees

• Current Assignee: Infrared Components Corporation
• Original Assignee: Infrared Components Corporation
• Inventors: Balick, Steven M., Knauth, Jonathan P.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/804,945
• Publication Number:
  US 20030146383A1
• Time in Patent Office: 938 Days
• Field of Search: 250/352
• US Class Current: 250/352
• CPC Class Codes: G01J 5/24 Use of specially adapted circuits, e.g. bridge circuits
• CPC Class Codes: H04N 25/21 for transforming thermal infrared radiation into image signals
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/677 for reducing the column or line fixed pattern noise
• 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 device for correction of microbolometer output, said device comprising:

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 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;

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 and;

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

2. The device of claim 1, 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.

3. The device of claim 1, wherein the first reference source is a voltage source.

4. The device of claim 3, wherein the voltage source is a digital-to-analog converter.

5. A microbolometer correction circuit comprising:

at least one microbolometer detector;

an analog-to-digital converter for converting the output of said microbolometer detector into a digital signal;

a signal processor programmed to apply an algorithm to said digital signal to generate a correction signal;

a memory device for storing said correction signal;

an electrical circuit for combining said correction signal with the output of said microbolometer detector;

a differential amplifier connected to the output of the microbolometer detector, said differential amplifier including a correction circuit to remove a pedestal voltage from the output of the microbolometer detector; and

an algorithm applied by the signal processor, said algorithm factoring in the responsivity of the microbolometer detector, and a corrective gain determined by the resistance in the microbolometer detector material.

6. The microbolometer correction circuit of claim 5, further comprising:

a calibration source positioned between said microbolometer detector and a infrared energy source.

7. The microbolometer correction circuit of claim 6, wherein said calibration source is operationally connected to an actuating device.

8. A microbolometer correction circuit comprising:

at least one microbolometer detector;

an analog-to-digital converter for converting the output of said microbolometer detector into a digital signal;

a signal processor programmed to apply an algorithm to said digital signal to generate a correction signal;

a memory device for storing said correction signal;

an electrical circuit for combining said correction signal with the output of said microbolometer detector; and

a cold shield situated substantially around said microbolometer detector.

9. A method for correction of the output of a microbolometer detection circuit comprising:

providing at least one microbolometer detector, said microbolometer detector connected to a reference circuit;

applying the output of said reference circuit to a signal processing system;

providing a temperature sensor operationally connected to said at least one microbolometer detector;

sensing the temperature of said microbolometer detector and producing a sensed temperature signal;

applying the sensed temperature signal to said signal processing system;

calculating a correction factor based on the outputs of said reference circuit and said sensed temperature signal;

combining said correction factor with said reference circuit output to produce a corrected signal; and

outputting said corrected signal.

10. The method of claim 9, further comprising:

including a correction circuit to remove a pedestal voltage from the output of the microbolometer detector;

applying an algorithm applied by the signal processor, said algorithm which factors in the responsivity of the microbolometer detector, and a corrective gain determined by the resistance in the microbolometer detector material;

placing a calibration device between the microbolometer detector and an calibration energy source;

exposing the microbolometer to the calibration energy source;

calibrating the at least one microbolometer detector; and

removing the calibration energy source and the calibration device.

11. A method for correction of the output of a focal plane array of microbolometer detectors employing continuous stabilization of the focal plane array temperature, said method comprising:

providing a system for thermal stabilization of the focal plane array;

sensing the focal plane array temperature;

applying a correction algorithm to correct the analog output of the focal plane array to bring the peak-to-trough value of the analog output within a sensitivity range of an analog-to-digital converter;

applying said corrected analog output to the first analog frame signals produced by the focal plane array to produce a resultant signal;

converting the resultant signal to digital data;

applying previously stored gain values to produce a corrected image signal; and

outputting the corrected image signal.

12. The method of claim 11, wherein the correction algorithm incorporates predetermined per-pixel offset data to calculate analog offset values.

13. The method of claim 11, wherein the step of converting the resultant signal to digital data includes the step of applying previously stored digital offset values.

14. The method of claim 11, wherein the system for thermal stabilization adjusts the temperature to a predetermined temperature.

15. The method of claim 14, wherein the predetermined temperature is determined by a calibration data set calculated for said focal plane array.

16. The method of claim 11, wherein the thermal stabilization is performed with the steps of:

sensing a preliminary focal plane array temperature at an initial period;

applying a temperature control means to the focal plane array;

stabilizing the focal plane array temperature at the preliminary temperature sensed at the initial period.

17. The method of claim 11, wherein the system for thermal stabilization includes a Peltier-junction heat engine.

18. A method for correction of the output of a focal plane array of microbolometer detectors employing passive stabilization of the focal plane array temperature, said method comprising:

providing a thermal mass upon which is mounted the focal plane array;

sensing a first focal plane array temperature;

applying a correction algorithm to correct the analog output of the focal plane array to bring the value of the analog output signal within a sensitivity range of an analog-to-digital converter;

applying the corrected analog output signal to the first analog frame signals produced by the focal plane array to produce a resultant signal;

converting the resultant signal to digital data;

applying previously stored gain values to the digital data to produce a corrected image signal; and

outputting the corrected image signal.

19. The method of claim 18, wherein the value of the analog output signal is the peak-to-peak value.

20. The method of claim 18, including the following steps:

sensing a second focal plane array temperature after the corrected image signal is outputted;

comparing the first and second focal plane array temperatures;

calculating a new correction algorithm if the difference between the first and second focal plane array temperatures exceeds an acceptable limit;

applying said new correction algorithm when the difference between the first and second focal plane array temperatures exceeds an acceptable limit.