Real-time adaptive thermal reference control for night vision systems

• US 5,920,066 A
• Filed: 07/16/1997
• Issued: 07/06/1999
• Est. Priority Date: 08/02/1996
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation), Texas Instruments, Inc.
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: DiRenzo, Michael T., Moizio, Frank J.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Israel, Andrew
• Application Number:
  US08/895,019
• Time in Patent Office: 720 Days
• Field of Search: 250/252.1, 250/332
• US Class Current: 250/252.1
• CPC Class Codes: G01J 5/48 Thermography; Techniques using wholly visual means
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• 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 system for normalizing an infrared detector has two control loops, each of which includes a thermal source and a command system. Each command system controls the temperature of the associated thermal source. Each command system includes an error signal source for providing an error signal indicative of the difference between a commanded temperature for the thermal source and an actual temperature at the thermal source, and includes a compensator coupled between the error signal source and the thermal source. Each compensator includes a first inverse compensation circuit responsive to the error signal for providing an output, a bandwidth maximizing compensation circuit responsive to the output of the first inverse compensation circuit, and a second inverse compensation circuit responsive to an output of the bandwidth maximizing compensation circuit. The thermal source is responsive to the output of the second inverse compensation circuit.

Claims

1. A system for normalization of an infrared detector having control loops, each said loop including a thermal source and a command system for controlling the temperature of said thermal source including:

(a) an error signal source for providing an error signal indicative of the difference between commanded temperature at said thermal source and actual temperature at said thermal source;

(b) a feedback path from said thermal source to said error signal source providing a signal responsive to the temperature of said thermal source; and

(c) a compensator coupled between said error signal source and said thermal source, said compensator including;

(i) a first inverse compensation circuit responsive to said error signal for providing an output;

(ii) a bandwidth maximizing compensation circuit responsive to the output of said first inverse compensation circuit; and

(iii) a second inverse compensation circuit responsive to an output of said bandwidth maximizing compensation circuit, said thermal source being responsive to an output of said second inverse compensation circuit.

2. The system of claim 1 wherein the thermal source in a first of said control loops is a gain thermal reference, wherein the thermal source in a second of said control loops is a level thermal reference, and wherein said first inverse compensation circuit operates in accordance with the formula:

##EQU5## where, Gain Ref Temp is the temperature of the gain thermal reference, Level Ref Temp is the temperature of the level thermal reference, Bits gain is the average output of the detector when viewing the gain thermal reference, and Bits level is the average output of the detector when viewing the level thermal reference.

3. The system of claim 2 wherein said bandwidth maximizing compensation circuit comprises a low pass filter, a non-linear gain section and a proportional plus integral filter.

4. The system of claim 3 wherein said non-linear gain section operates in accordance with the formula:

space="preserve" listing-type="equation">linear.sub.-- part=K.sub.-- linear*input

space="preserve" listing-type="equation">non.sub.-- linear.sub.-- part=input.sup.2 *sign (input)

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part>

limit1) then non.sub.-- linear.sub.-- part=limit1

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part<

limit2) then non.sub.-- linear.sub.-- part=limit2

space="preserve" listing-type="equation">output=linear.sub.-- part+non.sub.-- linear.sub.-- part;

where,

K_-- linear is a gain, and

limit1>

limit2.

5. The system of claim 4 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

6. The system of claim 5 wherein said bandwidth maximizing compensation circuit includes a combination of linear filter functions.

7. The system of claim 3 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

8. The system of claim 2 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

9. The system of claim 2 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=1, for all x.

10. The system of claim 2 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where g_est^-1 () is determined by using any well known method of approximating the input-output transfer function characteristics of said thermal reference.

11. The system of claim 1 wherein said bandwidth maximizing compensation circuit comprises a low pass filter, a non-linear gain section and a proportional plus integral filter.

12. The system of claim 11 wherein said non-linear gain section operates in accordance with the formula:

space="preserve" listing-type="equation">linear.sub.-- part=K.sub.-- linear*input

space="preserve" listing-type="equation">non.sub.-- linear.sub.-- part=input.sup.2 *sign (input)

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part>

limit1) then non.sub.-- linear.sub.-- part=limit1

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part<

limit2) then non.sub.-- linear.sub.-- part=limit2

space="preserve" listing-type="equation">output=linear.sub.-- part+non.sub.-- linear.sub.-- part;

where,

K_-- linear is a gain, and

limit1>

limit2.

13. The system of claim 12 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

14. The system of claim 11 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

15. The system of claim 1 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit, and x is the input to the second inverse compensation circuit.

16. The system of claim 1 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=1, for all x.

17. The system of claim 1 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output<

g.sub.est.sup.-1 (x)*x

where g_est^-1 () is determined by using any well known method of approximating the input-output transfer function characteristics of said thermal reference.

18. The system of claim 1 wherein said bandwidth maximizing compensation circuit includes a combination of linear filter functions.

19. A system for normalization of an infrared detector having a control loop, comprising a thermal source and a command system which controls the temperature of said thermal source and which includes:

(a) an error signal source for providing an error signal indicative of the difference between commanded temperature at said thermal source and actual temperature at said thermal source;

(b) a feedback path from said thermal source to said error signal source providing a signal responsive to the temperature of said thermal source; and

(c) a compensator coupled between said error signal source and said thermal source, said compensator including;

(i) a first inverse compensation circuit responsive to said error signal for providing an output;

(ii) a bandwidth maximizing compensation circuit responsive to the output of said first inverse compensation circuit; and

(iii) a second inverse compensation circuit responsive to an output of said bandwidth maximizing compensation circuit, said thermal source being responsive to an output of said second inverse compensation circuit.

20. The system of claim 19 wherein said first inverse compensation circuit operates in accordance with the formula:

##EQU6## where, Gain Ref Temp is the temperature of the gain thermal reference, Level Ref Temp is the temperature of the level thermal reference, Bits gain is the average output of the detector when viewing the gain thermal reference, and Bits level is the average output of the detector when viewing the level thermal reference.

21. The system of claim 19 wherein said bandwidth maximizing compensation circuit comprises a low pass filter, a non-linear gain section and a proportional plus integral filter.

22. The system of claim 21 wherein said non-linear gain section operates in accordance with the formula:

space="preserve" listing-type="equation">linear.sub.-- part=K.sub.-- linear*input

space="preserve" listing-type="equation">non.sub.-- linear.sub.-- part=input1*sign (input)

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part>

limit1) then non.sub.-- linear.sub.-- part=limit1

space="preserve" listing-type="equation">if (non.sub.-- linear.sub.-- part<

limit2) then non.sub.-- linear.sub.-- part=limit2

space="preserve" listing-type="equation">output=linear.sub.-- part+non.sub.-- linear.sub.-- part;

where,

K_-- linear is a gain, and

limit1>

limit2.

23. The system of claim 19 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=K1, for x≧

0

K2, for x<

0,

K₁ and K₂ are constants resulting from a curve fit approximating a transfer characteristic of said thermal source, and x is the input to the second inverse compensation circuit.

24. The system of claim 19 wherein said second inverse compensation circuit provides an output in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where,

g_est^-1 (x)=1, for all x.

25. The system of claim 19 wherein said second inverse compensation circuit provides said output thereof in accordance with the formula:

space="preserve" listing-type="equation">output=g.sub.est.sup.-1 (x)*x

where g^-1_set () is determined by using any well known method of approximating the input-output transfer function characteristics of said thermal reference.

26. The system of claim 19 wherein said bandwidth maximizing compensation circuit includes a combination of linear filter functions.

27. The system of claim 19, wherein said first inverse compensation circuit has a transfer function representative of an inverse of a non-linear characteristic of said infrared detector, wherein said second inverse compensation circuit has a transfer function representative of an inverse of a non-linear characteristic of said thermal source, and wherein said commanded temperature is a function of an average temperature of a scene viewed by said infrared detector.