Infrared Sensor Amplification Techniques for Thermal Imaging

• US 20140160299A1
• Filed: 12/10/2012
• Published: 06/12/2014
• Est. Priority Date: 12/10/2012
• Status: Active Grant

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Mumaw, David T.
• Granted Patent: US 9,438,825 B2
• Time in Patent Office: Days
• US Class Current: 348/164
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: H03G 1/0023 in emitter-coupled or cascode amplifiers H03G1/0029 takes precedence
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 23/50 Constructional details
• CPC Class Codes: H04N 23/51 Housings
• CPC Class Codes: H04N 23/63 by using electronic viewfinders
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/70 SSIS architectures; Circuits associated therewith
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 3/09 for electromagnetic radiation in the invisible region, e.g. infrared
• 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

Thermal imaging devices, systems, and methods are provided with IR sensor amplification techniques that in some cases provide a gain transfer function having at least two different gain regions. One thermal imaging camera includes an IR camera module, processing circuitry, and an amplifier stage that comprises a continuous gain function including at least two gain regions having different gains. In some cases a thermal imager is provided with saturation circuitry configured to reduce the gain of the amplifier stage in order to provide one of at least two different gain regions within the continuous gain function. In some cases amplification techniques provide a continuous gain function that includes both linear and nonlinear gain regions. One or more gain regions may further be calibrated for measuring temperature.

Claims

1. A thermal imaging camera, comprising:

an infrared (IR) camera module comprising an IR sensor for detecting IR radiation from a target scene, the IR sensor comprising a plurality of IR sensor elements arranged to receive the IR radiation from the target scene, each IR sensor element corresponding to part of a thermal image of the target scene and having an electrical characteristic that varies corresponding to an amount of the IR radiation received by the IR sensor element;

an amplifier stage coupled to the IR sensor for receiving a sensor output signal based on the electrical characteristic of one of the plurality of IR sensor elements, the amplifier stage comprising a gain provided according to a continuous gain function configured to amplify the sensor output signal through a continuous range of sensor output values to generate an amplifier output signal with a corresponding continuous range of amplifier output values, the continuous gain function comprising a first gain region having a first gain and a second gain region having a second gain different than the first gain; and

processing circuitry coupled to the amplifier stage, the processing circuitry configured to generate the thermal image of the target scene based on the amplifier output signal.

2. The thermal imaging camera of claim 1, wherein the amplifier stage further comprises an amplifier output range extending to a maximum amplifier output, wherein at least part of the second gain region generates amplifier output magnitudes less than the maximum amplifier output, wherein the first gain region generates amplifier output magnitudes less than the amplifier output magnitudes generated by the second gain region, and wherein the second gain region comprises a smaller gain than the first gain region.

3. The thermal imaging camera of claim 2, wherein the first gain region comprises a linear gain and the second gain region comprises a nonlinear gain.

4. The thermal imaging camera of claim 2, wherein the first gain region comprises a first linear gain and the second gain region comprises a second linear gain.

5. The thermal imaging camera of claim 4, wherein the continuous gain function further comprises a third gain region having a nonlinear gain and configured to generate amplifier output magnitudes less than the amplifier output magnitudes generated by the second gain region and more than the amplifier output magnitudes generated by the first gain region.

6. The thermal imaging camera of claim 2, wherein the amplifier stage further comprises saturation circuitry configured to reduce the gain of the amplifier stage to provide the second gain region.

7. The thermal imaging camera of claim 2, wherein the continuous range of sensor output values comprises a dynamic sensor output range corresponding to a dynamic temperature range for the target scene, wherein the continuous gain function maps the dynamic sensor output range to the amplifier output range to enable imaging of the dynamic temperature range for the target scene.

8. The thermal imaging camera of claim 7, wherein the dynamic temperature range for the target scene comprises a temperature of about −

30°

C. and a temperature of about 300°

C.

9. The thermal imaging camera of claim 7, wherein the dynamic temperature range for the target scene comprises a temperature of about −

30°

C. and a temperature of about 600°

C.

10. The thermal imaging camera of claim 1, wherein the amplifier stage is further configured to receive a sensor output signal corresponding to each IR sensor element, each sensor output signal based on the electrical characteristic of a corresponding IR sensor element, the amplifier stage configured to amplify each sensor output signal solely according to the continuous gain function.

11. The thermal imaging camera of claim 1, wherein at least one of the first gain region and the second gain region are calibrated for measuring temperatures of the target scene.

12. A thermal imaging apparatus, comprising:

an infrared (IR) camera module comprising an IR sensor for detecting IR radiation from a target scene, the IR sensor comprising a plurality of IR sensor elements arranged to receive the IR radiation from the target scene, each IR sensor element corresponding to part of a thermal image of the target scene and having an electrical characteristic that varies corresponding to an amount of the IR radiation received by the IR sensor element; and

an amplifier stage coupled to the IR sensor for receiving a sensor output signal based on the electrical characteristic of one of the plurality of IR sensor elements, the amplifier stage comprising

a gain for amplifying the sensor output signal to generate an amplifier output signal, the gain provided according to a continuous gain function configured to amplify the sensor output signal through a continuous range of sensor output values to generate the amplifier output signal with a corresponding continuous range of amplifier output values, and

saturation circuitry configured to reduce the gain of the amplifier stage according to the continuous gain function based on the amplifier output signal meeting a threshold value below a maximum amplifier output.

13. The thermal imaging apparatus of claim 12, wherein the amplifier stage comprises an amplifier output range extending to the maximum amplifier output, wherein the continuous gain function comprises a first gain region having a linear first gain and a second gain region provided by the saturation circuitry, the second gain region having a second gain smaller than the first gain.

14. The thermal imaging apparatus of claim 13, wherein the second gain comprises a nonlinear gain.

15. The thermal imaging apparatus of claim 13, wherein the continuous gain function further comprises a third gain region having a nonlinear gain and configured to generate amplifier output magnitudes less than amplifier output magnitudes generated by the second gain region and more than amplifier output magnitudes generated by the first gain region.

16. The thermal imaging apparatus of claim 13, wherein at least one of the first gain region and the second gain region are calibrated for measuring temperatures of the target scene.

17. The thermal imaging apparatus of claim 12, wherein the saturation circuitry comprises an amplifier feedback element configured to change states based on the amplifier output signal meeting the threshold value.

18. The thermal imaging apparatus of claim 17, wherein the amplifier stage comprises an amplifier with a resistive feedback loop, wherein the saturation circuitry comprises a zener diode in parallel with the resistive feedback loop, and wherein the threshold value comprises a breakdown voltage of the zener diode.

19. A method, comprising:

receiving a sensor output signal from an infrared (IR) sensor of a thermal imaging camera, the IR sensor comprising a plurality of IR sensor elements, the sensor output signal corresponding to an amount of infrared radiation received by one of the IR sensor elements from a target scene;

amplifying the sensor output signal with a gain of an amplifier stage to generate an amplifier output signal, the gain provided according to a continuous gain function configured to amplify the sensor output signal through a continuous range of sensor output values to generate the amplifier output signal with a corresponding continuous range of amplifier output values, the amplifying the sensor output signal comprising

if the sensor output signal is within a first range of sensor output signals, amplifying according to a first gain region of the continuous gain function, and

if the sensor output signal is within a second range of sensor output signals, amplifying according to a second gain region of the continuous gain function,

the second range of sensor output signals based on the amplifier output signal meeting a threshold value below a maximum amplifier output; and

generating a thermal image of the target scene based on the amplifier output signal.

20. The method of claim 19, wherein the amplifier stage comprises an amplifier output range extending to the maximum amplifier output, wherein at least part of the second gain region comprises a smaller gain than the first gain region and generates amplifier output magnitudes less than the maximum amplifier output, wherein the first gain region comprises a linear gain and generates amplifier output magnitudes less than the amplifier output magnitudes generated by the second gain region.

21. The method of claim 20, wherein the second gain region comprises a nonlinear gain.

22. The method of claim 20, wherein the continuous gain function further comprises a third gain region having a nonlinear gain and configured to generate amplifier output magnitudes less than the amplifier output magnitudes generated by the second gain region and more than the amplifier output magnitudes generated by the first gain region.

23. The method of claim 20, further comprising using the continuous gain function to map a dynamic temperature range for the target scene to the amplifier output range.

24. The method of claim 23, wherein the dynamic temperature range comprises a range of about 300°

C.

25. The method of claim 23, wherein the dynamic temperature range comprises a range of about 600°

C.

26. The method of claim 19, wherein at least one of the first gain region and the second gain region are calibrated for measuring temperatures of the target scene.