Display

• US 6,281,868 B1
• Filed: 01/25/1999
• Issued: 08/28/2001
• Est. Priority Date: 05/30/1997
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Takeuchi, Yukihisa, Nanataki, Tsutomu, Akao, Takayoshi, Ohwada, Iwao
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Osorio, Ricardo
• Application Number:
  US09/230,376
• Time in Patent Office: 946 Days
• Field of Search: 345/92, 345/91, 345/87, 345/89, 345/90, 310/328, 310/330, 310/331, 385/19, 385/129, 385/147
• US Class Current: 345/90
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0858 the reflecting means being moved or deformed by piezoelectric means
• CPC Class Codes: G09G 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3473 based on light coupled out of a light guide, e.g. due to scattering, by contracting the light guide with external means
• CPC Class Codes: G09G 3/3493 using light modulating elements actuated by a piezoelectric effect

Abstract

A switching TFT (thin-film transistor) 40 is disposed closely to an actuator 14 which comprises a lower electrode 28b, a shape holding layer 26, and an upper electrode 28a that are disposed on a vibrator. The upper electrode 28a of the actuator 14 is electrically connected through a contact 44 to a source/drain region 42 of the TFT 40. A gate line 46 and the gate electrode of the TFT 40 are electrically connected to each other through a contact 50. A data line 48 and a source/drain region 52 of the TFT 40 are electrically connected to each other through a contact 54. The TFT 40 may be replaced with a varistor or a piezoelectric relay. If a varistor is used, the off resistance of the varistor is preferably established such that a variation in a voltage applied to the actuator 14 due to a discharge owing to the off resistance in an unselected period is kept within 5%, and the on resistance of the varistor is preferably established such that a voltage applied to the actuator 14 increases to 95% in an effective selected period.

The display apparatus with actuators 14 having shape holding layers has low electric energy consumption and higher raster luminance, and allows wires or interconnections to be formed with ease.

Claims

1. A display apparatus having a light guide plate for introducing light therein and a driver disposed in confronting relation to a surface of the light guide plate and having an array of as many actuators as the number of pixels, the actuators being controlled for displacement into and out of contact with the light guide plate depending on an attribute of an inputted image signal to control leakage light from the light guide plate in predetermined areas for thereby displaying an image depending on the image signal on the light guide plate, characterized in that:

said driver has switching elements corresponding respectively to said actuators; and

said switching elements can be turned on and off to control the displacement of said actuators.

2. A display apparatus according to claim 1, wherein said driver has a board made of ceramics, said actuators being disposed on said board at positions aligned respectively with the pixels, said switching elements being disposed on said board.

3. A display apparatus according to claim 1 wherein each of said actuators comprises a shape holding layer, an operating unit disposed on said shape holding layer and having at least a pair of electrodes, a vibrator supporting said operating unit, and a mount member by which said vibrator is vibratingly supported, further comprising a displacement transfer unit for transferring the displacement of said actuator which is produced in response to the application of a voltage to said electrodes, to said light guide plate.

4. A display apparatus according to claim 1, further comprising:

a first drive circuit for selecting at least a row of said switching elements, a second drive circuit for outputting display information to the selected row of switching elements, and a signal control circuit for controlling said first drive circuit and said second drive circuit;

wherein said signal control circuit controls said first drive circuit and said second drive circuit to control gradations according to at least a time modulation process.

5. A display apparatus according to claim 4, wherein one image has a display period as one field, said display period having a selected period and an unselected period.

6. A display apparatus according to claim 4, wherein one image has a display period as one field, and said one field is divided into a plurality of subfields;

each of said subfields has a selected period and an unselected period; and

each of said subfields is set to a time length depending on a unit gradation level assigned to the subfield.

7. A display apparatus according to claim 6, wherein said first drive circuit is controlled for timing by said signal control circuit to finish the selection of all rows in each of said subfields;

said second drive circuit is controlled for timing by said signal control circuit to output data signals, which are produced by assigning display times depending on gradation levels of the pixels of the selected row to the subfields, to the pixels of the selected row in the selecting period of each of said subfields.

8. A display apparatus according to claim 7, wherein at least a reset period for substantially eliminating displayed luminance is provided between said effective display period in a subfield and said effective display period in a next subfield.

9. A display apparatus according to claim 7, wherein a reset period and an unselected period for substantially eliminating displayed luminance are provided between said effective display period in a subfield and said effective display period in a next subfield.

10. A display apparatus according to claim 7, wherein a preparatory period for stabilizing the operation of the actuators is provided immediately before said selected period.

11. A display apparatus according to claim 7, wherein a preparatory period for stabilizing the operation of the actuators is provided in said selected period.

12. A display apparatus according to claim 4, wherein said first drive circuit is capable of establishing at least three voltage levels, and said second drive circuit is capable of establishing at least two voltage levels.

13. A display apparatus according to claim 12, wherein said first drive circuit outputs a selecting pulse signal in said selected period, outputs an unselecting signal in said unselected period, and outputs a resetting pulse signal in said reset period;

said second drive circuit outputs an on signal in the selected periods in effective display periods in assigned subfields of said subfields, and outputs an off signal in the selected periods in effective display periods in other subfields.

14. A display apparatus according to claim 13, wherein a voltage sufficient to flexurally displace the actuator of a pixel to be controlled is applied to said actuator in a period in which said on signal is outputted;

and

a voltage sufficient to return said actuator from the displacement is applied to said actuator in a period in which said resetting pulse signal is outputted.

15. A display apparatus according to claim 13, wherein the absolute value of the difference between the maximum value of a voltage applied to said actuator of each pixel in said unselected period and the maximum value of a voltage applied to said actuator of each pixel by an off signal in said selected period is 100% or less of the absolute value of the difference between the maximum value of a voltage applied to said actuator of each pixel by an on signal in said selected period and the maximum value of a voltage applied to said actuator of each pixel by an off signal in said selected period.

16. A display apparatus according to claim 13, wherein said first drive circuit outputs a selecting window pulse to apply the voltage sufficient to flexurally displace said actuator of a pixel to be controlled to said actuator in combination with said on signal in said selected period.

17. A display apparatus according to claim 13, wherein said first drive circuit outputs a resetting window pulse to apply the voltage sufficient to return said actuator of a pixel to be controlled from the displacement, to said actuator in said reset period.

18. A display apparatus according to claim 13, wherein said first drive circuit outputs an unselecting window pulse to reduce the difference between average voltages applied in the unselected period to the actuators of the pixels, in said unselected period.

19. A display apparatus according to claim 13, wherein phase information is added to at least said on signal to reduce the difference between average voltages applied in the unselected period to the actuators of the pixels.

20. A display apparatus according to claim 19, wherein phase information is added to said selecting pulse signal and said on signal and/or said off signal.

21. A display apparatus according to claim 19, wherein phase information is added to said resetting signal.

22. A display apparatus according to claim 19, wherein said on signal and said off signal have a pulse duration smaller than an addressing time in said first drive circuit and are out of phase with each other by a predetermined angle.

23. A display apparatus according to claim 13, wherein at least either one of said on signal and said off signal has a pulse period which is 1/n (n is a real number ranging from 1 to 5) of said addressing time.

24. A display apparatus according to claim 1, wherein each of said switching elements comprises a transistor.

25. A display apparatus according to claim 1, wherein each of said switching elements comprises a piezoelectric relay.

26. A display apparatus having a light guide plate for introducing light therein and a driver disposed in confronting relation to a surface of the light guide plate and having an array of as many actuators as the number of pixels, the actuators being controlled for displacement into and out of contact with the light guide plate depending on an attribute of an inputted image signal to control leakage light from the light guide plate in predetermined areas for thereby displaying an image depending on the image signal on the light guide plate, characterized in that:

said driver has switching elements corresponding respectively to said actuators;

each of said switching elements comprises a varistor; and

said switching elements can be turned on and off to control the displacement of said actuators.

27. A display apparatus according to claim 26, wherein said driver has a board made of ceramics, said actuators being disposed on said board at positions aligned respectively with the pixels, said switching elements being disposed on said board.

28. A display apparatus according to claim 26, wherein each of said actuators comprises a shape holding layer, an operating unit disposed on said shape holding layer and having at least a pair of electrodes, a vibrator supporting said operating unit, and a mount member by which said vibrator is vibratingly supported, further comprising a displacement transfer unit for transferring the displacement of said actuator, which is produced in response to the application of a voltage to said electrodes, to said light guide plate.

29. A display apparatus according to claim 26, further comprising:

a first drive circuit for selecting at least a row of said switching elements, a second drive circuit for outputting display information to the selected row of switching elements, and a signal control circuit for controlling said first drive circuit and said second drive circuit;

wherein said signal control circuit controls said first drive circuit and said second drive circuit to control gradations according to at least a time modulation process.

30. A display apparatus according to claim 29, wherein one image has a display period as one field, said display period having a selected period and an unselected period.

31. A display apparatus according to claim 29, wherein one image has a display period as one field, and said one field is divided into a plurality of subfields;

each of said subfields has a selected period and an unselected period; and

each of said subfields is set to a time length depending on a unit gradation level assigned to the subfield.

32. A display apparatus according to claim 31, wherein said first drive circuit is controlled for timing by said signal control circuit to finish the selection of all rows in each of said subfields;

said second drive circuit is controlled for timing by said signal control circuit to output data signals, which are produced by assigning display times depending on gradation levels of the pixels of the selected row to the subfields, to the pixels of the selected row in the selecting period of each of said subfields.

33. A display apparatus according to claim 32, wherein at least a reset period for substantially eliminating displayed luminance is provided between said effective display period in a subfield and said effective display period in a next subfield.

34. A display apparatus according to claim 32, wherein a reset period and an unselected period for substantially eliminating displayed luminance are provided between said effective display period in a subfield and said effective display period in a next subfield.

35. A display apparatus according to claim 32, wherein a preparatory period for stabilizing the operation of the actuators is provided immediately before said selected period.

36. A display apparatus according to claim 32, wherein a preparatory period for stabilizing the operation of the actuators is provided in said selected period.

37. A display apparatus according to claim 29, wherein said first drive circuit is capable of establishing at least three voltage levels, and said second drive circuit is capable of establishing at least two voltage levels.

38. A display apparatus according to claim 33, wherein said first drive circuit outputs a selecting pulse signal in said selected period, outputs an unselecting signal in said unselected period, and outputs a resetting pulse signal in said reset period;

said second drive circuit outputs an on signal in the selected periods in effective display periods in assigned subfields of said subfields, and outputs an off signal in the selected periods in effective display periods in other subfields.

39. A display apparatus according to claim 38, wherein a voltage sufficient to flexurally displace the actuator of a pixel to be controlled is applied to said actuator in a period in which said on signal is outputted;

and

a voltage sufficient to return said actuator from the displacement is applied to said actuator in a period in which said resetting pulse signal is outputted.

40. A display apparatus according to claim 38, wherein the absolute value of the difference between the maximum value of a voltage applied to said actuator of each pixel in said unselected period and the maximum value of a voltage applied to said actuator of each pixel by an off signal in said selected period is 100% or less of the absolute value of the difference between the maximum value of a voltage applied to said actuator of each pixel by an on signal in said selected period and the maximum value of a voltage applied to said actuator of each pixel by an off signal in said selected period.

41. A display apparatus according to claim 38, wherein said first drive circuit outputs a selecting window pulse to apply the voltage sufficient to flexurally displace said actuator of a pixel to be controlled to said actuator in combination with said on signal in said selected period.

42. A display apparatus according to claim 38, wherein said first drive circuit outputs a resetting window pulse to apply the voltage sufficient to return said actuator of a pixel to be controlled from the displacement, to said actuator in said reset period.

43. A display apparatus according to claim 38, wherein said first drive circuit outputs an unselecting window pulse to reduce the difference between average voltages applied in the unselected period to the actuators of the pixels, in said unselected period.

44. A display apparatus according to claim 38, wherein phase information is added to at least said on signal to reduce the difference between average voltages applied in the unselected period to the actuators of the pixels.

45. A display apparatus according to claim 44, wherein phase information is added to said selecting pulse signal and said on signal and/or said off signal.

46. A display apparatus according to claim 44, wherein phase information is added to said resetting signal.

47. A display apparatus according to claim 44, wherein said on signal and said off signal have a pulse duration smaller than an addressing time in said first drive circuit and are out of phase with each other by a predetermined angle.

48. A display apparatus according to claim 38, wherein at least either one of said on signal and said off signal has a pulse period which is 1/n (n is a real number ranging from 1 to 5) of said addressing time.

49. A display apparatus according to claim 26, wherein said varistor has an off resistance established such that a variation in a voltage applied to said actuator due to a discharge in the unselected period is kept within 5%;

and

said varistor has an on resistance established such that a voltage applied to said actuator increases to 95% in an effective selected period.