Optical modulation or image display system

• US 6,037,922 A
• Filed: 06/12/1996
• Issued: 03/14/2000
• Est. Priority Date: 06/15/1995
• Status: Expired due to Fees

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Yagyu, Mineto
• Primary Examiner(s): Saras, Steven J.
• Assistant Examiner(s): ENGLISH, ALECIA DIANE
• Application Number:
  US08/661,958
• Time in Patent Office: 1,371 Days
• Field of Search: 345/4, 345/6, 345/87, 345/96, 349/25, 349/31, 365/108, 353/31, 348/739
• US Class Current: 345/89
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2360/142 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

An optical modulation unit is constituted by a light source periodically turned on, and an optical modulation means including an optical modulation element and periodically turned on. The optical modulation unit is driven by changing a voltage applied to the optical modulation element depending on given graduation data so as to modulate an overlapping time between an ON period of the optical modulation means and a lighting period of the light source. The gradation data may be analog gradation data and may be carried by light illuminating the optical modulation element synchronized with a voltage applied to the optical modulation element.

Claims

1. A driving method for an optical modulation unit including a light source periodically turned on and optical modulation means including an optical modulation element that is periodically turned on, said driving method comprising the step of:

changing an amplitude of a voltage applied to the optical modulation element depending on given gradation data so as to modulate an overlapping time between an ON period of the optical modulation means and a lighting period of the light source in order to effect an analog duty-modulated gradational display scheme.

2. A driving method according to claim 1, wherein the voltage applied to the optical modulation means is changed with time.

54. A driving method according to any of claims 1, 13, 14 and 15, wherein the overlapping time is modulated within a range up to a maximum duty of at most 1/2.

55. A driving method according to any of claims 1, 13, 14 and 15, wherein the overlapping time for each of a plurality of colors is modulated within a range up to a maximum duty of at most 1/6.

56. A driving method according to any of claims 1, 13, 14 and 15, wherein the optical modulation element comprises a reflecting member capable of changing its reflecting surface direction.

58. A method according to any one of claims 1, 13, 14, and 16-19, wherein a pulse width in addition to the amplitude of the voltage is changed depending on the given gradation data.

3. An optical modulation apparatus, comprising:

a light source periodically turned on;

optical modulation means including an optical modulation element that is periodically turned on; and

drive means for driving said optical modulation means by changing an amplitude of a voltage applied to the optical modulation element depending on given gradation data so as to modulate an overlapping time between an ON period of said optical modulation means and a lighting period of said light source in order to effect an analog duty-modulated gradational display scheme.

4. An apparatus according to claim 3, wherein said drive means includes means for changing the voltage applied to the optical modulation element with time.

5. An apparatus according to claim 3, wherein said drive means includes

means for applying a drive voltage to said optical modulation means, and

means for changing the drive voltage with time.

6. An apparatus according to claim 3, wherein said drive means includes a capacitance element and a resistance element for modulating the overlapping time.

7. An apparatus according to claim 3, wherein the optical modulation element comprises a liquid crystal that has two optical states.

8. An apparatus according to claim 3, wherein the optical modulation element comprises a chiral smectic liquid crystal.

9. An apparatus according to claim 3, wherein the optical modulation element comprises one of a ferroelectric and an anti-ferroelectric liquid crystal.

10. An apparatus according to claim 3, wherein said light source is a white light source.

11. An apparatus according to claim 3, wherein said light source includes a red light source, a blue light source, a green light source, and lighting means for energizing the red, blue, and green light sources in mutually different periods.

12. An apparatus according to claim 3, wherein the gradation data is carried by light data.

59. An apparatus according to claim 3, wherein a pulse width in addition to the amplitude of the voltage is changed depending on the given gradation data.

60. An apparatus according to claim 3, wherein said drive means includes a parallel circuit comprising a capacitance element C_PC and a resistance element disposed in parallel with a capacitance C_LC of said optical modulation means so as to provide a variable discharge time determined by a time constant of the parallel circuit and depending on the given gradation data.

13. A driving method for an optical modulation unit including a light source periodically turned on and optical modulation means comprising a plurality of optical modulation elements arranged in a plane, wherein each of the optical modulation elements is periodically turned on, said driving method comprising the step of:

changing an amplitude of a voltage applied to an optical modulation element depending on given gradation data so as to modulate an overlapping time between an ON period of the optical modulation element and a lighting period of the light source in order to effect an analog duty-modulated gradational display scheme.

39. A driving method according to any of claims 13-19, wherein the light source comprises a white light source.

40. A driving method according to any of claims 13-19, wherein the light source is one that successively emits red light, green light, and blue light.

43. A driving method according to any of claims 13-19, wherein a reset voltage is applied to the optical modulation means.

44. A driving method according to any of claims 13, 14, and 16-19, wherein the optical modulation means is reset and then is illuminated with light data carrying gradation data in synchronism with a writing voltage applied to the optical modulation means thereby to be supplied with the voltage with an amplitude that changes with time.

45. A driving method according to any of claims 13-19, wherein the optical modulation means is reset and then is illuminated with light data carrying gradation data in synchronism with a voltage having a maximum peak value in a period for applying a writing voltage to the optical modulation means.

46. A driving method according to any of claims 13-19, wherein the optical modulation means is reset and then is illuminated with light data carrying gradation data only for an initial period within a period for applying a writing voltage to the optical modulation means.

47. A driving method according to any of claims 13-19, wherein the optical modulation means is reset then is illuminated with light data carrying gradation data only for an initial period within a period for applying a writing voltage to the optical modulation means, and thereafter the writing voltage applied to the optical modulation means is gradually changed.

48. A driving method according to any of claims 13-19, wherein the optical modulation means is supplied with light data carrying the gradation data and bias light not depending on the gradation data.

49. A driving method according to any of claims 13-19, wherein the optical modulation means is supplied with light data carrying the gradation data and then is supplied with bias light not depending on the gradation data.

50. A driving method according to any of claims 13-19, wherein the optical modulation means is supplied with a reset voltage prior to illumination with the light data carrying the gradation data.

51. A driving method according to any of claims 13-19, wherein the optical modulation means is supplied with a reset voltage prior to illumination with the light data carrying the gradation data, and is further illuminated with bias light.

14. A driving method for an optical modulation unit including a light source periodically turned on and optical modulation means comprising a planar optical modulation element that is periodically turned on, said driving method comprising the step of:

changing an amplitude of a voltage applied to a local region of the planar optical modulation element depending on given gradation data so as to modulate an overlapping time between an ON period of the optical modulation element and a lighting period of the light source in order to effect an analog duty-modulated gradational display scheme.

15. A driving method for an optical modulation unit including optical modulation means comprising a pair of electrodes, and a photoelectric conversion layer and an optical modulation element disposed between the pair of electrodes, a signal light source for supplying light data carrying gradation data to the photoelectric conversion layer, and a readout light source for supplying readout light to the optical modulation element, said driving method comprising the step of:

controlling a lighting time of the readout light source to modulate an overlapping time between a period when the optical modulation element assumes a prescribed optical state and the lighting time depending on given gradation data in order to effect an analog duty-modulated gradational display scheme.

21. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with an optical modulation substance and a non-single crystal semiconductor disposed between the electrodes.

22. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with a chiral smectic liquid crystal and a non-single crystal semiconductor disposed between the electrodes.

23. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with a chiral nematic liquid crystal substance and a non-single crystal semiconductor disposed between the electrodes.

24. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with a ferroelectric liquid crystal and a photoelectric conversion substance disposed between the electrodes.

25. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with an optical modulation substance and a non-single crystal silicon material disposed between the electrodes.

26. A driving method according to any of claims 15-19, wherein the optical modulation means comprises a pair of electrodes with a chiral smectic liquid crystal and a non-single crystal silicon-germanium material disposed between the electrodes.

27. A driving method according to any of claims 15-19, wherein the light source is turned on in synchronism with a commencement of application of a writing voltage after a resetting operation.

28. A driving method according to any of claims 15-19, wherein the light source is turned off before switching from the second optical state to the first optical state.

29. A driving method according to any of claims 15-19, wherein the light source is energized only for a period corresponding to a modulation range of timing when the optical modulation element is switched from the first optical state to the second optical state.

30. A driving method according to any of claims 15-19, wherein when the gradation data corresponds to a minimum or maximum gradation level the light source is turned on in synchronism with a commencement of application of a writing voltage after a resetting operation and is turned off prior to switching from the first optical state to the second optical state.

31. A driving method according to any of claims 15-19, wherein when the gradation data corresponds to a minimum or maximum gradation level the light source is turned on in synchronism with a commencement of application of a writing voltage after a resetting operation and is turned off prior to switching from the second optical state to the first optical state.

32. A driving method according to any of claims 15-19, wherein the light source is repetitively turned on at a cycle period shorter than a flickering frequency cycle period.

33. A driving method according to any of claims 15-19, wherein the light source emits mutually different wavelengths of light sequentially and selectively at a cycle period shorter than a flickering frequency cycle period.

52. A driving method according to any of claims 15-19, wherein the optical modulation means is illuminated with the light data carrying the gradation data for a period different from the lighting period of the light source.

16. A driving method for driving an optical modulation unit including a light source and optical modulation means comprising an optical modulation element, said driving method comprising the steps of:

applying to the optical modulation element a voltage with an amplitude that changes with time depending on given gradation data, thereby modulating a timing when the optical modulation element is switched from a first optical state to a second optical state; and

turning on the light source to obtain light data subjected to analog duty modulation depending on the gradation data in order to effect an analog duty-modulated gradational display scheme.

20. A driving method according to claim 16, wherein the optical modulation means comprises a pair of electrodes between which the optical modulation element and a photoelectric conversion substance are disposed.

34. A driving method according to any of claims 16-19, wherein the voltage applied to the optical modulation element is polarity-inverted to provide a DC component of substantially zero within a prescribed period, and the light source is energized for a lighting period shorter than the prescribed period.

41. A driving method according to any of claims 16-19, wherein the voltage applied to the optical modulation element is a voltage that causes a polarity inversion and that has a DC component of substantially zero within a prescribed period.

42. A driving method according to any of claims 16-19, wherein the voltage applied to the optical modulation element is a voltage that causes a polarity inversion and that has a DC component of substantially zero within a prescribed period, and the voltage is applied in a cycle period shorter than a flickering frequency cycle period.

53. A driving method according to any of claims 16-19, wherein the optical modulation means is supplied with a first the voltage simultaneously with illumination with the light data carrying the gradation data, and is then supplied with a second voltage different from first the voltage after the illumination.

17. A driving method for an optical modulation unit including a light source and optical modulation means comprising an optical modulation element that assumes bistable states, a photoelectric conversion substance, and a pair of electrodes sandwiching the optical modulation element and the photoelectric conversion substance, said driving method comprising the steps of:

applying a voltage between the pair of electrodes, and

supplying to the optical modulation element light data carrying gradation data to the photoelectric conversion substance so as to apply a voltage having an amplitude that changes with time depending on the gradation data, thereby modulating a period between switching from a first stable state to a second stable state to switching from the second stable state to the first stable state, respectively, of the optical modulation element, the period being modulated within a range having a maximum set to be shorter than a prescribed period so as to allow recognition of a change in gradation level, in order to effect an analog duty-modulated gradational display scheme.

35. A driving method according to any of claims 17-19, wherein the prescribed period or continuous lighting period of the light source is at most 1/30 sec.

36. A driving method according to any of claims 17-19, wherein the prescribed period or continuous lighting period of the light source is at most 1/60 sec.

37. A driving method according to any of claims 17-19, wherein the prescribed period or continuous lighting period of the light source is at most 1/90 sec.

38. A driving method according to any of claims 17-19, wherein the prescribed period or continuous lighting period of the light source is at most 1/180 sec.

18. A driving method for an optical modulation unit including a light source and optical modulation means comprising an optical modulation element, a photoelectric conversion substance, and a pair of electrodes sandwiching the optical modulation element and the photoelectric conversion substance, said driving method comprising the steps of:

applying a voltage between the pair of electrodes, supplying to the optical modulation element light data carrying gradation data to the photoelectric conversion substance so as to apply a voltage with an amplitude that changes with time depending on the gradation data, thereby modulating a timing of switching from a first optical state to a second optical state in an analog manner; and

turning on the light source so as to provide a lighting time within a range having a maximum period set to be shorter than a prescribed period so as to allow recognition of a change in gradation level in order to effect an analog duty-modulated gradational display scheme.

61. A method according to claim 18, wherein the optical modulation element is driven in a succession of cycle periods so that the optical modulation element is placed in the first and second optical states for equal periods within each cycle period.

62. A method according to claim 61, wherein the optical modulation element comprises one of a ferroelectric and an anti-ferroelectric liquid crystal.

19. A driving method for an optical modulation unit including a light source and optical modulation means comprising an optical modulation element, a photoelectric conversion substance, and a pair of electrodes sandwiching the optical modulation element and the photoelectric conversion substance, said driving method comprising the steps of:

repetitively applying a voltage between the pair of electrodes, the voltage causing a polarity inversion and having a DC component of substantially zero within a prescribed period;

supplying light data carrying gradation data to the photoelectric conversion substance; and

applying to the optical modulation element a voltage with an amplitude that changes with time depending on the gradation data to the optical modulation element to modulate a timing of switching from a first optical state to a second optical state, thereby turning on the light source in either a former half or a latter half of the prescribed period, in order to effect an analog duty-modulated gradational display scheme.

57. A driving method for an image display unit including an optical modulation device comprising a pair of electrodes for application of a voltage therebetween, and a photoconductor layer and an optical modulation element disposed between the pair of electrodes, a signal light source for supplying light information carrying gradation data to the photoconductor layer, and a readout light source for supplying readout light for reading out image data to the optical modulation element, said driving method comprising the step of:

operating the readout light source in a lighting period controlled to be different from a period of supplying the light information, thereby modulating an overlapping time between a period in which the optical modulation element assumes a prescribed optical state and the lighting period depending on the gradation data in order to effect an analog duty-modulated gradational display scheme.