Digital offset corrector

• US 6,879,923 B2
• Filed: 06/14/2001
• Issued: 04/12/2005
• Est. Priority Date: 05/26/1998
• Status: Expired due to Term

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Butler, Neal R.
• Primary Examiner(s): NGHIEM, MICHAEL P
• Application Number:
  US09/881,648
• Publication Number:
  US 20020022938A1
• Time in Patent Office: 1,398 Days
• Field of Search: 702/79, 702/85, 702/104, 702/124, 250/208.1, 250/208.2, 250/252.1, 250/332, 250/338.1, 250/370.08
• US Class Current: 702/104
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• 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 25/673 by using reference sources
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• 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

Offset correction methods and apparatus for a focal plane array. A bolometer array configured in a row and column readout format has dedicated column circuits to measure the resistance of each bolometer in the column. A high speed on-chip analog to digital converter converts the analog sensor signal to a digital representation. Various offset control methods and apparatus are employed to correct the digital representation for variations in individual bolometer response that are not necessarily associated with signals of interest.

Claims

1. Apparatus comprising:

a first sensor of an array of sensors to detect radiation and to output a first image signal based on the radiation detected by the first sensor; and

offset correction circuitry to compensate errors in at least the first image signal and to output at least a corrected first image signal,

wherein the offset correction circuitry includes means for providing at least one time-varying compensation signal that is added to the first image signal to generate the corrected first image signal;

wherein the apparatus comprises a plurality of sensors including the first sensor, the plurality of sensors outputting respective image signals based on the radiation detected by each sensor of the plurality of sensors, and

wherein the means for providing at least one time-varying compensation signal includes means for providing, a different time-varying compensation signal for each of at least two sensors of the array of sensors.

2. The apparatus of claim 1, wherein:

the means for providing at least one time-varying compensation signal includes a capacitor; and

the at least one time-varying compensation signal is based on a charging and a discharging of the capacitor.

3. The apparatus of claim 1, wherein the means for providing at least one time-varying compensation signal includes a compensating source to compensate changes in at least the first image signal due to current-induced heating of at least the first sensor.

4. The apparatus of claim 1, wherein the means for providing at least one time-varying compensation signal includes means for providing a variable current.

5. The apparatus of claim 4, wherein the means for providing the variable current includes means for adding the variable current to the first image signal such that an average value of the variable current and the first image signal remains essentially constant during a signal sampling period.

6. The apparatus of claim 1, wherein the means for providing at least one time-varying compensation signal includes means for providing a variable voltage.

7. The apparatus of claim 6, wherein the means for providing the variable voltage includes means for adding the variable voltage to the first image signal such that an average value of the variable voltage and the first image signal remains essentially constant during a signal sampling period.

8. A method for compensating errors in a first image signal generated by a first sensor of an array of sensors in response to radiation detected by the first sensor, comprising a step of:

a) adding a time-varying compensation signal to the first image signal;

wherein a plurality of sensors including the first sensor generate respective image signals including the first signal in response to radiation detected by each sensor of the plurality of sensors, and

wherein the act a) includes an act of;

adding a different time-varying compensation signal to each of at least two respective image signals of at least two sensors of the array of sensors.

9. The method of claim 8, wherein the time-varying compensation signal is a variable current.

10. The method of claim 8, wherein the time-varying compensation signal is a variable voltage.

11. The method of claim 8, wherein the step of adding includes a step of generating the time-varying compensation signal by charging and discharging a capacitor in a predetermined manner based on the first image signal.

12. The method of claim 8, wherein the step of adding includes a step of generating the time-varying compensation signal such that an average value of the time-varying compensation signal and the first image signal remains essentially constant during a signal sampling period.

13. The method of claim 12, wherein the time-varying compensation signal is a variable current.

14. The method of claim 12, wherein the time-varying compensation signal is a variable voltage.

15. The method of claim 8, wherein a plurality of sensors including the first sensor generate respective image signals including the first signal in response to radiation detected by each sensor of the array of sensors, and wherein the act a) includes an act of:

generating the time-varying compensation signal based on non-uniformities of the sensors.

16. The method of claim 8, wherein the step of adding includes a step of generating the time-varying compensation signal based on changes in the first image signal due to current-induced heating of at least the first sensor.

17. An apparatus, comprising:

a first sensor of an array of sensors adapted to generate a first image signal in response to radiation detected by the first sensor; and

at least one signal generator configured to add a first time-varying compensation signal to the first image signal so as to provide an adjusted first image signal; and

a plurality of sensors including the first sensor, the plurality of sensors adapted to generate respective image signals including the first signal in response to radiation detected by each sensor of the plurality of sensors,

wherein the at least one signal generator is configured to add a different time-varying compensation signal to each of at least two respective image signals of at least two sensors of the array of sensors so as to provide at least two adjusted image signals.

18. The apparatus of claim 17, wherein the first sensor is a microbolometer.

19. The apparatus of claim 17, wherein the at least one signal generator is configured to generate the first time-varying compensation signal as a variable current.

20. The apparatus of claim 17, wherein the at least one signal generator is configured to generate the first time-varying compensation signal as a variable voltage.

21. The apparatus of claim 17, wherein the at least one signal generator includes at least one capacitor, the at least one signal generator being configured to generate the first time-varying compensation signal by charging and discharging the at least one capacitor in a predetermined manner based on the first image signal.

22. The apparatus of claim 17, wherein the at least one signal generator is configured to provide the adjusted first image signal such that an average value of the adjusted first image signal remains essentially constant during a sampling period.

23. The apparatus of claim 22, wherein the at least one signal generator is configured to generate the first time-varying compensation signal as a variable current.

24. The apparatus of claim 22, wherein the at least one signal generator is configured to generate the first time-varying compensation signal as a variable voltage.

25. The apparatus of claim 17,

wherein the at least one signal generator is configured to generate at least the first time-varying compensation signal based on non-uniformities of the sensors.

26. The apparatus of claim 17, wherein the at least one signal generator is configured to generate the first time-varying compensation signal based on changes in the first image signal due to current-induced heating of at least the first sensor.