Constant light disable for spatial light modulator

• US 6,683,290 B2
• Filed: 12/28/2001
• Issued: 01/27/2004
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Doherty, Donald B.
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Lee, Patrick J.
• Application Number:
  US10/033,332
• Publication Number:
  US 20020121588A1
• Time in Patent Office: 760 Days
• Field of Search: 250/214.R, 250/214.C, 250/214.AG, 250/214.RC, 250/201.1, 327/514-515, 356/221-223, 356/226, 356/209, 359/239, 359/291, 359/292
• US Class Current: 250/201.1
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 3/34 by control of light from an independent source
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal
• CPC Class Codes: H04N 9/3179 Video signal processing therefor

Abstract

A method and system of detecting whether the intensity of light incident a spatial light modulator varies periodically. One embodiment provides a method of operating a spatial light modulator, the method comprising: determining a peak level of light incident the modulator over a period of time; setting a threshold level equal to a fraction of the peak level; monitoring a current level of light incident the modulator; comparing the current level of light and the threshold level; and disabling the modulator based on the comparison. Another embodiment provides a modulator array. The modulator comprises: a photosensitive circuit for outputting a light intensity signal representative of a level of light incident the photosensitive circuit; a threshold detection circuit 400 receiving the light intensity signal 402 and outputting an under threshold signal 408 indicative of whether the intensity signal is less than a threshold level; and a duty cycle detection circuit 410 for monitoring the under threshold signal 408 and outputting a disable signal 418 indicative of the duty cycle of the under threshold signal 408. The preceding abstract is submitted with the understanding that it only will be used to assist in determining, from a cursory inspection, the nature and gist of the technical disclosure as described in 37 C.F.R. §1.72(b). In no case should this abstract be used for interpreting the scope of any patent claims.

Claims

1. A method of operating a spatial light modulator, the method comprising:

determining a peak level of light incident said modulator over a period of time;

setting a threshold level equal to a fraction of said peak level;

monitoring a current level of light incident said modulator;

comparing said current level of light and said threshold level; and

disabling said modulator based on said comparison.

2. The method of claim 1, said determining a peak level of light incident said modulator over a period of time comprising:

generating a signal representing said incident light level;

detecting a peak of said signal representing said incident light level.

3. The method of claim 1, said determining a peak level of light incident said modulator over a period of time comprising:

generating a voltage signal representing said incident light level using a photodiode.

4. The method of claim 1, said determining a peak level of light incident said modulator over a period of time comprising:

generating a voltage signal representing said incident light level using a phototransistor.

5. The method of claim 1, said determining a peak level of light incident said modulator over a period of time comprising:

generating a voltage signal representing said incident light level; and

scaling said voltage signal.

6. The method of claim 5, said setting a threshold level equal to a fraction of said peak level comprising:

setting said threshold level equal to a fraction of said scaled voltage signal.

7. The method of claim 1, said setting a threshold level equal to a fraction of said peak level comprising:

dividing said peak level using a voltage divider.

8. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal when said current level is greater than said threshold level.

9. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal when said current level is less than said threshold value.

10. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal, a magnitude of which varies with a result of said comparison.

11. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal indicating whether said current level is less than or greater than said threshold value.

12. The method of claim 1, said disabling said modulator based on said comparison comprising:

disabling said modulator when said comparison shows said current level is below said threshold value for a predetermined period of time.

13. The method of claim 1, said disabling said modulator based on said comparison comprising:

disabling said modulator when said comparison shows said current level is above said threshold value for an entire said period of time.

14. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal indicating whether said current level is less than or greater than said threshold value; and

said disabling said modulator based on said comparison comprising;

disabling said modulator when a duty cycle of said voltage signal falls below a threshold.

15. The method of claim 1, said comparing said current level of light and said threshold level comprising:

generating a voltage signal indicating whether said current level is less than or greater than said threshold value; and

said disabling said modulator based on said comparison comprising;

disabling said modulator when a duty cycle of said voltage signal is above a threshold.

16. The method of claim 1, said disabling said modulator based on said comparison comprising:

incrementing a counter when said current level is less than said threshold value.

17. The method of claim 1, said disabling said modulator based on said comparison comprising:

incrementing a counter when said current level is greater than said threshold value.

18. The method of claim 1, said disabling said modulator based on said comparison comprising:

decrementing a counter when said current level is less than said threshold value.

19. The method of claim 1, said disabling said modulator based on said comparison comprising:

decrementing a counter when said current level is greater than said threshold value.

20. The method of claim 1, said disabling said modulator based on said comparison comprising:

adding a first scale factor to a first previous sum value using a first adder when said current level is less than said threshold value;

adding a second scale factor to a second previous sum value using a second adder when said current level is greater than said threshold value;

incrementing a counter upon a carry condition in said first adder;

decrementing said counter upon a carry condition in said second adder; and

disabling said modulator when said counter reaches a limit.

21. The method of claim 1, said disabling said modulator based on said comparison comprising:

adding a first scale factor to a first previous sum value using a first adder when said current level is less than said threshold value;

adding a second scale factor to a second previous sum value using a second adder when said current level is greater than said threshold value;

decrementing a counter upon a carry condition in said first adder;

incrementing said counter upon a carry condition in said second adder; and

disabling said modulator when said counter reaches a limit.

22. A modulator array comprising:

a photosensitive circuit for outputting a light intensity signal representative of a level of light incident said photosensitive circuit;

a threshold detection circuit receiving said light intensity signal and outputting an under threshold signal indicative of whether said intensity signal is less than a threshold level; and

a duty cycle detection circuit for monitoring said under threshold signal and outputting a disable signal indicative of the duty cycle of said under threshold signal.

23. The modulator array of claim 22, wherein said photosensitive circuit is operable to output an analog signal.

24. The modulator array of claim 22, said threshold detection circuit further comprising a peak detection circuit for determining a peak value of said light intensity signal.

25. The modulator array of claim 22, said threshold detection circuit further comprising:

a peak detection circuit for determining a peak value of said light intensity signal; and

a threshold generation circuit for generating a threshold value dependent on said peak value.

26. The modulator array of claim 22, said duty cycle detection circuit further comprising:

a counter for counting a first direction when said under threshold signal is a first polarity.

27. The modulator array of claim 26, wherein said duty cycle detection circuit generates said disable signal when said counter reaches a predetermined value.

28. The modulator array of claim 26, wherein said counter counts in said first direction in steps greater than one.

29. The modulator array of claim 26, wherein said counter counts in said first direction when said under threshold signal is a first polarity and a periodic signal is active.

30. The modulator array of claim 22, said duty cycle detection circuit further comprising:

a counter for counting a first direction when said under threshold is logic true and a second direction when said under threshold signal is a second polarity.

31. The modulator array of claim 30, wherein said duty cycle detection circuit generates said disable signal when said counter reaches a predetermined value.

32. The modulator array of claim 31, wherein said counter counts in said first direction in steps greater than one.

33. The modulator array of claim 31, wherein said counter counts in said second direction in steps greater than one.

34. The modulator array of claim 31, wherein said counter counts in said first direction when said under threshold signal is a first polarity and a periodic signal is active.

35. The modulator array of claim 31, wherein said counter counts in said second direction when said under threshold signal is a second polarity and a periodic signal is active.

36. The modulator array of claim 22, said duty cycle detection circuit further comprising:

a first counter for counting when said under threshold signal is a first polarity;

a second counter for counting when said under threshold signal is a second polarity; and

a third counter for counting in a first direction when said first counter reaches a first number and counting in a second direction when said second counter reaches a second number, said disable signal generated when said third counter reaches a third number.

37. The modulator array of claim 36, said first counter comprising:

a latch for holding a sum; and

an adder for adding a first number to an output of said latch to generate said sum.

38. The modulator array of claim 37, wherein said adder generates a carry signal and said third counter counting in said first direction when said adder generates said carry signal.

39. The modulator array of claim 36, said second counter comprising:

a latch for holding a sum; and

an adder for adding a second number to an output of said latch to generate said sum.

40. The modulator array of claim 39, wherein said adder generates a carry signal and said third counter counts in said second direction when said adder generates said carry signal.

41. The modulator array of claim 36, wherein said first, second, and third counters count when a periodic signal is active.

42. The modulator array of claim 36, wherein said first, second, and third counters count when a particular row decode signal is active.

43. The modulator array of claim 22, said duty cycle detection circuit further comprising:

a counter for counting a first direction when said under threshold signal is a first polarity and resetting when said under threshold signal is a second polarity.

44. The modulator array of claim 22, comprising:

a means of enabling or disabling said duty cycle detection circuit.

45. The modulator array of claim 22, comprising:

a fuse to disable said duty cycle detection circuit.

46. The modulator array of claim 22, wherein said duty cycle detection circuit is enabled or disabled by the package bond-out.

47. The modulator array of claim 22, comprising:

a means of enabling or disabling said threshold detection circuit.

48. The modulator array of claim 22, comprising:

a fuse to disable said threshold detection circuit.

49. The modulator array of claim 22, wherein said threshold detection circuit is enabled or disabled by the package bond-out.