Apparatus and method for compensating for pixel non-uniformity in a bolometer

• US 6,690,013 B2
• Filed: 08/22/2002
• Issued: 02/10/2004
• Est. Priority Date: 05/05/2000
• Status: Expired due to Term

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Infrared Solutions, Inc. (Fortive Corp.)
• Inventors: McManus, Timothy J.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US10/225,768
• Publication Number:
  US 20030006374A1
• Time in Patent Office: 537 Days
• Field of Search: 250/330, 250/332, 250/338.1, 250/339.09, 250/342, 250/252.1
• US Class Current: 250/338.1
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: H04N 25/63 applied to dark current
• 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

In accordance with the present invention, a microbolometer focal plane array is provided with at least one thermally-shorted microbolometer detector that is thermally shorted to the microbolometer focal plane array substrate. A characteristic relationship is empirically derived for determining a corrected resistance value for each detector of the microbolometer focal plane array in response to radiation from a target scene as a function of the corresponding detector resistance value, the thermally-shorted microbolometer detector resistance value, and the empirically derived characteristic relationship.

Claims

1. An uncooled infrared camera comprising:

a microbolometer focal plane array associated with a substrate responsive to a target scene through a selected lens, wherein said microbolometer focal plane array includes,

a plurality, N, of substantially substrate-isolated microbolometer detectors, each exhibiting a resistance value, Rⁿ, in response to the radiation temperature radiated from said sensed target scene, where n represents a unique one of said N detectors, and

at least one temperature sensor for providing an output signal having a value, RS(T), substantially indicative of sensed substrate temperature, T;

a controllable shutter open in one state permitting the microbolometer focal plane array to be responsive to a scene, and closed in a second state subjecting the microbolometer focal plane array to a uniform temperature scene;

a readout circuit for a outputting a corresponding measurement value indicative of the resistance value associated with each of the substrate-isolated detectors;

means for storing unique characteristic information, qⁿ, associated with each nth one of said N substrate-isolated microbolometer detectors, where said characteristic information qⁿ provides information for correcting the resistance value Rⁿ of the nth one of said substrate-isolated microbolometer detectors as a function of said sensed substrate temperature, T; and

data processor means for determining a corrected target temperature resistance value Xⁿ for each of said N detectors, where Xⁿ is a function of said resistance value, Rⁿ, said characteristic information, qⁿ, and said value RS(T) indicative of said substrate temperature.

2. The camera of claim 1 wherein:

said unique characteristic information, qⁿ, is in the form of at least a data pair describing at least a first coefficient mⁿ and a constant bⁿ associated with the nth one of said plurality of detectors, and

said data processor means includes means for determining said corrected target temperature resistance value Xⁿ substantially in accordance with the mathematical expression;

3. The camera of claim 1 wherein:

said unique characteristic information, qⁿ, is in the form of a plurality of look-up data tables where each table is a set of N cells, and where each cell corresponds to a selected n^th one of said N detectors, and where each cell contains offset error data Eⁿ(T_k) associated with said nth detector at temperature T_k indicated by said temperature detector value RS(T_k); and

said data processor means includes means for determining said corrected target temperature resistance value Xⁿ(T), for each of said N detectors, substantially in accordance with the mathematical expression;

$X^n<br><br>\left(T\right)=R^n<br><br>\left(T\right)-\left\{E^n@\mathrm{RS}<br><br>\left(T\right)+[\text{\hspace{1em}<br><br>}<br><br>R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T\right)-R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T_k\right)]*\frac{\left[E^n@R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T_{k+1}\right)-E^n@R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T_k\right)\right]}{\left[R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T_{k+1}\right)-R<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(T_k\right)\right]}\right\}$

 

where T is between T_k+1 and T_k, and Eⁿ@RS(T_k+1), Eⁿ@RS(T_k) are the offset values associated with corresponding tables T_k+1 and T_k.

4. The camera of claim 1:

wherein each of said N detectors and is electrically connected to an electrical bias source, and

said microbolometer imaging apparatus further includes a bias control processor for providing said electrical bias source in relation to said temperature detector having value RS(T).

5. The camera of claim 1 wherein said characteristic information consists of at least a pair of constants b and m for determining said corrected target temperature resistance Xⁿ substantially in accordance with the following mathematical expression:

6. The camera of claim 5 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values Rⁿ of said N detectors and said temperature detector value, RS(T), as said focal plane array is subjected to a uniform scene temperature at differing ones of said substrate temperature, I.

11. The camera of claim 1 wherein said temperature sensor is a at least one thermally-shorted microbolometer detector thermally shorted to said substrate, and exhibiting a resistance value, RS(T), substantially indicative of sensed substrate temperature, T.

12. The camera of claim 1 wherein said temperature sensor is a temperature sensor exhibiting a resistance value, RS(T), substantially indicative of sensed substrate temperature, T.

7. A method for correcting the indicated resistance value Rⁿ of each substrate-isolated microbolometer of a focal plane array including a plurality, N, of substrate-isolated microbolometer detectors on a substrate, the method comprising the steps of:

empirically deriving a characteristic relationship between the resistance of each of said microbolometer detectors, Rⁿ, and the temperature of said substrate having a value numerically indicated by RS(T), where T is the substrate temperature;

determining a corrected resistance value for each detector of the microbolometer focal plane array in response to radiation from a target scene as a function of the corresponding detector resistance value Rⁿ, the value RS(T); and

said empirically derived characteristic relationship.

8. The method of claim 7 wherein said characteristic relationship is ma thematically describes by:

9. The method of claim 8 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and the temperature of the substrate indicated by RS(T) as said focal plane array is subjected to a uniform scene temperature at differing ones of said substrate temperature.

13. The method of claim 7 further including a temperature sensor in the form of a at least one thermally-shorted microbolometer detector thermally shorted to said substrate, and exhibiting a resistance value, RS(T), substantially indicative of sensed substrate temperature, T.

14. The method of claim 13 wherein said temperature sensor is a temperature sensor exhibiting a resistance value, RS(T), as a function of sensed substrate temperature, T.

10. A method for providing correction to for an uncooled infrared camera employing a microbolometer focal plane array of substrate isolated microbolometers where the array includes a plurality, N, of substrate-isolated microbolometer detectors on a substrate, and where associated with each of the detectors is a resistance value Rⁿ,the method comprising the steps of:

empirically deriving a characteristic relationship between the resistance of each of said microbolometer detectors, Rⁿ, and the sensed substrate temperature, T;

determining a corrected resistance value for each detector of the microbolometer focal plane array in response to radiation from a target scene as a function of the corresponding detector resistance value Rⁿ, said sensed substrate temperature; and

said empirically derived characteristic relationship.

15. A microbolometer imaging apparatus responsive to a target scene comprising:

a microbolometer focal plane array associated with a substrate, and which said microbolometer focal plane array includes,

a plurality, N, of substantially substrate-isolated microbolometer detectors, each exhibiting a unique resistance value, Rⁿ, in response to the radiation temperature radiated from said sensed target scene, where n represents a unique one of said N detectors; and

at least one temperature sensor having an output characteristic related to the substrate temperature, T;

a data processor means for determining a corrected target temperature resistance value Xⁿ for each of said N detectors, where Xⁿ is derived from a function of said resistance value, Rⁿ, and a function of said sensed substrate temperature, T.

16. The apparatus of claim 15 where the corrected target temperature resistance value Xⁿ is charcterizied by at least a pair of constants b and m for determining said corrected target temperature resistance Xⁿ substantially in accordance with the following mathematical expression.

17. The apparatus of claim 16 above wherein said constants mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and said sensed substrate temperature as said focal plane array is subjected to differing uniform scene substrate temperatures.

18. The apparatus of claim 15 above further including:

a plurality of look-up tables having unique correction values Eⁿ(T_k) associated with each of said N detectors corresponding to a selected substrate temperature T_k, and where each of said correction values is empirically determined from raw resistance values Rⁿ of said N detectors and said sensed substrate temperature in response to said focal plane array being subjected to a uniform scene temperature at differing ones of said substrate temperature, T, where each of said tables corresponds to a selected substrate temperature, T_k; and

where each of said tables provides said correction value Eⁿ(T_k) for each of said N detectors for selected substrate temperatures, T_k, such that said corrected target temperature resistance values Xⁿ(T) are substantially derived from a function of,

(i) said resistance value Rⁿ(T),

(ii) an estimated detector correction value Eⁿ(T), derived from selected ones of said plurality of look-up tables, and

(iii) said sensed substrate temperature T.

19. A microbolometer correction method for correcting indicated raw resistance value Rⁿ of each n^th one of a plurality of N substrate-isolated microbolometer detectors on a substrate of a focal plane array, the method comprising the steps of:

empirically determining separately for each n_th one of said N substrate-isolated microbolometer detectors unique characteristic information qⁿ for deriving a corrected resistance value Xⁿ(T) as a function of sensed substrate temperature T;

determining resistance values Rⁿ(T) for each one of said N substrate-isolated microbolometer detectors in response to radiation from a target scene; and

correcting each of said subsequent resistance values Rⁿ(T) as a function of sensed substrate temperature, and said characteristic information qⁿ.

20. The method of claim 19 further comprising the step of establishing a look up table descriptive of said characteristic information, where each of said tables corresponds to a selected substrate temperature T_k.

21. The method of claim 19:

wherein each of said N detectors is electrically connected to an electrical bias source, and

said method includes the step of adjusting said electrical bias source in response to said sensed substrate temperature.

22. The method of claim 19 wherein said characteristic information consists of at least a pair of constants b and m for determining said corrected target temperature resistance Xⁿ substantially in accordance with the following mathematical expression:

23. The method of claim 22 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and said sensed substrate temperature as said focal plane array is subjected to a uniform scene temperature at differing ones of said substrate temperature, and where n corresponds to said nth detector.

24. A microbolometer imaging apparatus responsive to a target scene comprising:

a microbolometer focal plane array associated with a substrate, and which said microbolometer focal plane array includes,

a plurality, N, of substantially substrate-isolated microbolometer detectors, each exhibiting a unique resistance value, Rⁿ, in response to the radiation temperature radiated from said sensed target scene, where n represents a unique one of said N detectors; and

at least one temperature sensor having an output characteristic related to the substrate temperature, T;

a data processor means for determining a corrected target temperature resistance value Xⁿ(T) for each of said N detectors, where Xⁿ(T) is a function of

(i) said resistance value, Rⁿ,

(ii) a plurality of look up tables having unique correction values Eⁿ(T_k), where each table is associated with selected ones of substrate temperatures T_k, and

(iii) said sensed substrate temperature T.

25. The apparatus of claim 24 wherein:

said plurality of look-up tables are empirically determined from raw resistance values Rⁿ of said N detectors and said sensed temperature of said substrate in response to said focal plane array being subjected to a uniform scene temperature at differing ones of said substrate temperature, T, where each of said tables corresponds to a selected substrate temperature, T_k; and

each of said tables provides a correction value Eⁿ(T_k) for each of said N detectors for selected substrate temperatures, T_k, such that said corrected target temperature resistance values Xⁿ(T) are substantially derived from a function of,

(i) said resistance value Rⁿ(T),

(ii) an estimated detector correction value Eⁿ(T), derived from selected ones of said plurality of look-up tables, and

(iii) said sensed substrate temperature.

26. The method of claim 25 further comprising the step of subjecting said focal plane array temporarily to a uniform temperature scene by way of opening and closing a shutter.

27. The method of claim 26 further comprising the step of applying a 2-point correction scheme.

28. A microbolometer imaging apparatus responsive to a target scene comprising:

a microbolometer focal plane array associated with a substrate, and which said microbolometer focal plane array includes,

a plurality, N, of substantially substrate-isolated microbolometer detectors, each exhibiting a resistance value, Rⁿ, in response to the radiation temperature radiated from said sensed target scene, where n represents a unique one of said N detectors; and

at least one temperature sensor having an output characteristic related to the substrate temperature, T;

means for storing unique characteristic information, qⁿ, associated with each nth one of said N substrate-isolated microbolometer detectors, where said characteristic information qⁿ provides information for correcting the resistance value Rⁿ of the nth one of said substrate-isolated microbolometer detectors as a function of said sensed substrate temperature, T; and

data processor means for determining a corrected target temperature resistance value Xⁿ for each of said N detectors, where Xⁿ is a function of said resistance value, Rⁿ, said characteristic information, qⁿ, and said sensed substrater temperature, T.

29. The apparatus of claim 28 wherein:

said unique characteristic information, qⁿ, is in the form of at least a data pair describing at least a first coefficient mⁿ and a constant bⁿ associated with the nth one of said plurality of detectors, and

said data processor means includes means for determining said corrected target temperature resistance value Xⁿ substantially in accordance with the mathematical expression;

30. The apparatus of claim 28 wherein:

said unique characteristic information, qⁿ, is in the form of a plurality of look-up data tables where each table is a set of N cells, and where each cell corresponds to a selected n^th one of said N detectors, and where each cell contains offset error data Eⁿ(T_k) associated with said nth detector at temperature T_k indicated by said temperature sensor having a value RS(T_k); and

said data processor means includes means for determining said corrected target temperature resistance value Xⁿ(T), for each of said N detectors, substantially in accordance with the mathematical expression;