Microbolometer focal plane array with controlled bias

• US 6,538,250 B2
• Filed: 07/05/2002
• Issued: 03/25/2003
• Est. Priority Date: 10/07/1999
• Status: Expired due to Term

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Infrared Solutions, Inc. (Fortive Corp.)
• Inventors: Anderson, Shane M., McManus, Timothy J.
• Primary Examiner(s): MAI, HUY KIM
• Application Number:
  US10/198,295
• Publication Number:
  US 20020185601A1
• Time in Patent Office: 263 Days
• Field of Search: 250/332, 250/338.1, 250/338.4, 250/370.08, 250/252.1
• US Class Current: 250/332
• CPC Class Codes: H01L 27/14649 Infrared imagers
• CPC Class Codes: H01L 27/14669 Infrared imagers
• CPC Class Codes: H04N 25/673 by using reference sources
• 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 controlling bias for an microbolometer focal plane array which includes use of one thermally-shorted microbolometer detector thermally shorted to the substrate upon which one or more thermally-isolated microbolometers are constructed. A calibration bias source magnitude is determined and continually adjusted as a function of (i) the temperature related reading value of the resistance of the thermally-shorted microbolometer at calibration, and (ii) the temperature related reading value of the resistance of the thermally-shorted microbolometer after each image sample is taken.

Claims

1. A method for controlling bias for an microbolometer focal plane array associated with a substrate, and which said microbolometer focal plane array includes a plurality of substrate-isolated microbolometer detectors and one thermally-shorted microbolometer detector thermally shorted to said substrate, and wherein associated with said microbolometer focal plane array is a circuit means, including an electric signal bias source, for determining, for each of said microbolometer detectors, a reading value representative of the corresponding temperature associated therewith, the method comprising the steps of:

setting the magnitude said electric signal bias source to a bias source calibration magnitude such that an average value representative of the average of each reading value associated with all of said substrate-isolated microbolometer detectors at a calibration instant of time is substantially at a selected value within a selected reading value range at a calibration instant of time;

determining a bias temperature reference reading value representative of the temperature of said thermally-shorted microbolometer detector at substantially said calibration instant of time;

determining a bias temperature reference reading value representative of the temperature of said thermally-shorted microbolometer detector at selected instants of time subsequent to said calibration instant of time;

adjusting said bias electric signal source to an operating magnitude value, where said operating magnitude value is substantially equal to the sum of;

(i) said bias source calibration magnitude, and

(ii) a selected scale factor multiplied by the difference between

a. said bias temperature reference reading value at said calibration instant of time, and

b. said bias temperature reference reading value corresponding to a last occurring one of said selected instants of time.

2. The method of claim 1 wherein said electric signal bias source is a voltage source.

3. The method of claim 1 wherein said electric signal bias source is a current source.

4. The method of claim 1 wherein said selected scale factor is empirically determined.

5. The method of claim 1 wherein said average value representative of the average of each reading value associated with all of said substrate-isolated microbolometer detectors at a calibration instant of time is substantially at the mid-point of said selected range.

6. A microbolometer imaging apparatus comprising:

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

a plurality of substrate-isolated microbolometer detectors each having a resistance value related to its sensed temperature thereof, and

one thermally-shorted microbolometer detector thermally shorted to said substrate, and having a resistance value related to its sensed temperature thereof;

circuit means associated with said microbolometer focal plane array for determining, for of each of said microbolometer detectors, a reading value representative of the corresponding temperature associated therewith, said circuit means including means for providing an electric signal bias source selectively coupled to each of said microbolometers for separately passing a current through each of said microbolometer detectors;

bias source control means for controlling the operation magnitude value of said electric signal bias source, said bias control means including,

means for initializing said electric signal bias source to a calibration magnitude at a calibration instant of time,

means for determining a bias temperature reference reading value representative of the temperature of said thermally-shorted microbolometer detector at substantially said calibration instant of time,

means for determining a bias temperature reference reading value representative of the temperature of said thermally-shorted microbolometer detector at selected instants of time subsequent to said calibration instant of time, and

means for setting said operating magnitude value of said electric signal bias source substantially equal to the sum of;

(i) said bias source calibration magnitude, and

(ii) a selected scale factor (S) multiplied by the difference between

a. said bias temperature reference reading value at said calibration instant of time, and

b. said bias temperature reference reading value corresponding to a last occurring one of said selected instants of time.

7. The apparatus of claim 6 wherein said electric signal bias source is a voltage source.

8. The apparatus of claim 6 wherein said electric signal bias source is a current source.

9. The apparatus of claim 6 wherein said bias source control means includes a digital-to-analog converter for receiving digital information representative of desired magnitude of said electric signal bias source and outputting an analog value representative thereof.

10. The method of claim 6 wherein said selected scale factor (S) is empirically determined.

11. The method of claim 6 wherein said calibration magnitude is selected such that that an average value, representative of the average of each reading value associated with all of said substrate-isolated microbolometer detectors, at said calibration instant of time, is substantially at a midpoint of a selected reading value range.

12. The method of claim 6 wherein said calibration magnitude is selected such that that an average value, representative of the average of each reading value associated with all of said substrate-isolated microbolometer detectors, at said calibration instant of time, is substantially at a selected operating point within a selected reading value range, thereof.

13. The method of claim 12 wherein said average value, representative of the average of each reading value associated with all of said substrate-isolated microbolometer detectors, at said calibration instant of time, is substantially at the mid-point within said selected reading value range.