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

• US 6,465,785 B1
• Filed: 05/05/2000
• Issued: 10/15/2002
• 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, Geogia
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US09/567,568
• Time in Patent Office: 893 Days
• Field of Search: 250/330, 250/332, 250/338.1, 250/339.09, 250/342
• 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. 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 thermally-shorted microbolometer detector thermally shorted to said substrate, and exhibiting a resistance value, RS(T), substantially indicative of sensed 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 resistance value of said thermally-shorted microbolometer detector RS(T).

2. The apparatus 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 apparatus 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 n^th detector at temperature T_k indicated by said thermally-shorted microbolometer detector resistance 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;

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

 

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 apparatus 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 thermally-shorted microbolometer detector resistance value RS(T).

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

7. 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 thermally-shorted microbolometer detector thermally shorted to said substrate, and exhibiting a resistance value, RS(T), substantially indicative of sensed substrate temperature, T; and

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 resistance value of said thermally-shorted microbolometer detector RS(T).

8. The apparatus of claim 7 wherein:

said plurality of look-up tables are empirically determined from raw resistance values Rⁿ of said N detectors and said resistance value of thermally-shorted microbolometer detector RS(T) in response to said focal plane array being subjected to a constant 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 thermally-shorted microbolometer detector resistance value, RS(T).

9. 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 thermally-shorted microbolometer detector thermally shorted to said substrate, and exhibiting a resistance value, RS(T), substantially indicative of sensed 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 said thermally-shorted microbolometer detector resistance value RS(T).

10. The apparatus of claim 9 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:

11. The apparatus of claim 10 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and sid thermally-shorted microbolometer detector as said focal plane array is subjected to a constant scene temperature at differing ones of said substrate temperature.

12. The apparatus of claim 9 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 thermally-shorted microbolometer detector RS(T) in response to said focal plane array being subjected to a constant 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 thermally-shorted microbolometer detector resistance value RS(T).

13. 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 including at least one thermally-shorted microbolometer detector thermally shorted to said substrate, 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 the resistance value RS(T) of at least one thermally-shorted microbolometer detector at a 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 the resistance value RS(T) of said thermally-shorted microbolometer detector, and said characteristic information qⁿ.

14. The method of claim 13 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.

15. The method of claim 13:

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

said method includes the step of adjusting said electrical bias source in response to said thermally-shorted microbolometer detector resistance value RS(T).

16. The method of claim 13 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:

17. The method of claim 16 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and said thermally-shorted microbolometer detector as said focal plane array is subjected to a constant scene temperature at differing ones of said substrate temperature, and where n corresponds to said nth detector.

18. The method of claim 16 wherein the step of determining said characteristic information includes,

the step of deriving a plurality of look-up tables having unique correction values Eⁿn(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 thermally-shorted microbolometer detector RS(T) in response to said focal plane array being subjected to a constant 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 thermally-shorted microbolometer detector resistance value RS(T).

19. A method for correcting the indicated resistance value Rⁿ of each substrate-isolated microbolometer of a focal plane array including (i) a plurality, N, of substrate-isolated microbolometer detectors on a substrate, and (ii) one thermally-shorted microbolometer detector thermally shorted to said substrate, the method comprising the steps of:

empirically deriving a characteristic relationship between the resistance of each of said microbolometer detectors, Rⁿ, and the resistance value of said substrate-isolated microbolometer RS(T_k);

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 thermally-shorted microbolometer detector resistance value RS(T_k); and

said empirically derived characteristic relationship.

20. The method of claim 19 wherein said characteristic relationship is mathematically describes by:

21. The method of claim 20 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and said thermally-shorted microbolometer detector as said focal plane array is subjected to a constant scene temperature at differing ones of said substrate temperature.

22. A microbolometer correction method for correcting the indicated resistance value Rⁿ of each n^th substrate-isolated microbolometer of a focal plane array including (i) a plurality, N, of substrate-isolated microbolometer detectors on a substrate, and (ii) at least one thermally-shorted microbolometer detector thermally shorted to said substrate, the method comprising the steps of:

empirically deriving for each n^th detector a characteristic relationship between the resistance of each of said microbolometer detectors, Rⁿ, and the resistance value of said substrate-isolated microbolometer RS(T), where T is substantially said substrate temperature; and

determining a corrected resistance value Xⁿ for each n^th 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 thermally-shorted microbolometer detector resistance value RS(T); and

said empirically derived characteristic relationship.

23. The method of claim 22 wherein said characteristic relationship is mathematically describes by:

24. The method of claim 23 wherein said value mⁿ and bⁿ are empirically determined from raw resistance values of said N detectors and said thermally-shorted microbolometer detector as said focal plane array is subjected to a constant scene temperature at differing ones of said substrate temperature, T.