Infrared sensor amplification techniques for thermal imaging

• US 9,438,825 B2
• Filed: 12/10/2012
• Issued: 09/06/2016
• 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.
• Primary Examiner(s): Pe, Geepy
• Assistant Examiner(s): Hasan, Syed Y.
• Application Number:
  US13/710,024
• Publication Number:
  US 20140160299A1
• Time in Patent Office: 1,366 Days
• Field of Search: 348/164, 348/E3.01, 348/E5.09, 348/166, 348/167, 348/201, 250/252.1, 250/330, 250/332, 250/338.1, 250/338.4, 250/339.04, 250/334, 330/254
• US Class Current: 1/1
• 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 23/50 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 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 configured to produce an IR sensor element output signal based on 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 the IR sensor element output signals from each of the plurality of IR sensor elements,

the amplifier stage comprising a gain provided according to a continuous gain function configured to amplify the IR sensor element output signals from each of the plurality of IR sensor elements through a continuous range of IR sensor element output values to generate amplifier output signals corresponding to each of the plurality of IR sensor elements, the amplifier output signals having 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,

wherein the first gain region is applied to a first range of IR sensor element output values and generates a corresponding first range of amplifier output values and the second gain region is applied to a second range of IR sensor element output values and generates a corresponding second range of amplifier output values; 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 signals.

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 IR sensor element 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 configured to amplify each IR sensor element 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 configured to produce an IR sensor element output signal based on 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 the IR sensor element output signals from each of the plurality of IR sensor elements, the amplifier stage comprising a gain for amplifying the IR sensor element output signal from each of the plurality of IR sensor elements to generate amplifier output signals corresponding to each of the plurality of IR sensor elements, the gain provided according to a continuous gain function having a first gain region and a second gain region and configured to amplify the each of the IR sensor element output signals through a continuous range of IR sensor element output values to generate the corresponding amplifier output signals with a corresponding continuous range of amplifier output values, and

saturation circuitry configured to, for each of the IR sensor element output signals, reduce the gain of the amplifier stage according to the continuous gain function in the event that the corresponding amplifier output signal meets a threshold value below a maximum amplifier output such that, for each of the IR sensor elements, if the first gain region applied to the IR sensor element output signal results in the corresponding amplifier output signal meeting the threshold value, the saturation circuitry reduces the gain applied to that IR sensor element output signal so that the second gain region is applied to the IR sensor element output signal; and

processing circuitry coupled to the amplifier stage and configured to generate the thermal image of the target scene based on each of the amplifier output signals corresponding to the respective IR sensor element output signals from each of the plurality of IR sensor elements.

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 first gain region includes a linear first gain and the second gain region includes 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 in the event that one of the amplifier output signals meets 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 plurality of IR sensor element output signals corresponding to an amount of infrared radiation received by each of a plurality of IR sensor elements from a target scene, each of the IR sensor elements corresponding to a part of a thermal image of the target scene;

amplifying each of the IR sensor element output signals with a gain of an amplifier stage to generate a plurality of amplifier output signals, each of the plurality of amplifier output signals corresponding to one of the plurality of IR sensor elements, the gain provided according to a continuous gain function configured to amplify each of the IR sensor element output signals through a continuous range of IR sensor element output values to generate the corresponding amplifier output signal with a corresponding continuous range of amplifier output values, wherein for each of the IR sensor element output signals, the amplifying of the IR sensor element output signal comprises;

if the IR sensor element output signal is within a first range of IR sensor element output signals, applying a first gain region of the continuous gain function to the IR sensor element output signal to generate an amplifier output value within a corresponding first range of amplifier output values, and

if the IR sensor element output signal is within a second range of IR sensor element output signals, applying a second gain region of the continuous gain function to the IR sensor element output signal to generate an amplifier output value within a corresponding second range of amplifier output values, wherein

the second range of IR sensor element output signals comprises IR sensor element output signals such that applying the first gain region to such IR sensor element output signals generates amplifier output values that exceed a threshold value, the threshold value being below a maximum amplifier output value; and

generating a thermal image of the target scene based at least on the plurality of amplifier output signals.

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.