Active matrix liquid crystal image generator

• US 7,170,483 B2
• Filed: 05/12/2003
• Issued: 01/30/2007
• Est. Priority Date: 12/22/1994
• Status: Expired due to Fees

• Current Assignee: Citizen Finetech Miyota Company Limited (Citizen Electronics Company Limited)
• Original Assignee: Displaytech Inc (Micron Technology, Inc.)
• Inventors: Handschy, Mark A., Meadows, Michael R.
• Primary Examiner(s): DeCady; Albert
• Assistant Examiner(s): Alphonse; Fritz
• Application Number:
  US10/437,131
• Publication Number:
  US 20050052388A1
• Time in Patent Office: 1,359 Days
• Field of Search: 345/89, 345/97, 345/98, 345/690, 359/224, 359/230, 359/291, 359/630
• US Class Current: 345/89
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/133622 Colour sequential illumination
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence
• CPC Class Codes: G02F 1/136277 formed on a semiconductor substrate, e.g. of silicon
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 2203/12 spatial light modulator
• CPC Class Codes: G02F 2203/30 Gray scale
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2310/0278 Details of driving circuits arranged to drive both scan and data electrodes
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2029 the sub-frames having non-binary weights
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals

Abstract

A system for producing spatially modulated monochrome or color light having gray scale includes an active matrix liquid crystal spatial light modulator having light modulating means including (i) a layer of ferroelectric liquid crystal material which is designed to switch between ON and OFF states and (ii) active matrix means including VLSI circuitry for dividing the layer of liquid crystal material into an array of individual liquid crystal pixels and for causing each of the pixels of liquid crystal material to modulate light individually by switching between the ON and OFF states in a way that depends upon the data which the VLSI circuitry is written. The system also includes illumination means having a light source for directing light from the source into the pixel-divided layer of ferroelectric liquid crystal material in a specific way. And finally, the system includes means for writing the VLSI circuitry with preselected data in accordance with a particular data ordering scheme such that the circuitry, in response to the written data, causes the pixels of liquid crystal material to individually switch between their ON and OFF states and therefore modulate light from the source in a way which, depending upon the data, produces a specific overall pattern of gray scale light.

Claims

1. A system for producing modulated light having gray scale, comprising:

a spatial light modulator having an array of pixels switchable between only two different optical states;

a light source that illuminates the spatial light modulator for only approximately one-half of the time that the system is operating; and

a data writing arrangement that writes data to the pixels of the spatial light modulator, to cause the pixels to individually switch to one of the two different optical states, so as to modulate light from the light source in a way to produce an overall pattern of gray scale light;

wherein the gray scale produced is related to the timing of the writing operations.

2. A system as defined in claim 1, wherein the spatial light modulator is a microdisplay.

3. A system as defined in claim 2, wherein the spatial light modulator is embodied on a silicon substrate.

4. A system as defined in claim 3, wherein adjacent pixels in the spatial light modulator have a pitch of 10 μ

m or less.

5. A system as defined in claim 1, wherein the spatial light modulator reflects light from the light source to produce an overall pattern of gray scale light.

6. A system as defined in claim 1, wherein each pixel has a pixel electrode associated therewith, and the data writing arrangement causes the pixel electrodes to switch to one of two different voltage levels that differ by an amount less than 26 volts.

7. A system as defined in claim 1, wherein the spatial light modulator includes liquid crystal material.

8. A system as defined in claim 1, wherein the liquid crystal material has a thickness of less than 2 μ

m.

9. A system as defined in claim 1, wherein the pixels of the spatial light modulator have a response time of less then 2 ms.

10. A system as defined in claim 1, wherein the system produces a full color image with the single spatial light modulator by sequentially producing images of three different colors.

11. A system for producing modulated light having gray scale, comprising:

a spatial light modulator having an array of pixels switchable between different light modulating states, each pixel having a pixel electrode associated therewith;

a light source; and

a data writing arrangement that writes data to the pixels of the spatial light modulator, to cause the pixel electrodes of the spatial light modulator to switch to one of only two different voltage levels that differ by an amount less than or equal to 5 volts, to cause the pixels to individually change states so as to modulate light from the light source in a way to produce an overall pattern of gray scale light.

12. A system as defined in claim 11, wherein the spatial light modulator is a microdisplay.

13. A system as defined in claim 12, wherein the spatial light modulator is embodied on a silicon substrate.

14. A system as defined in claim 13, wherein adjacent pixels in the spatial light modulator have a pitch of 10 μ

m or less.

15. A system as defined in claim 11, wherein the spatial light modulator reflects light from the light source to produce an overall pattern of gray scale light.

16. A system as defined in claim 11, wherein the spatial light modulator includes liquid crystal material.

17. A system as defined in claim 16, wherein the liquid crystal material has a thickness of less than 2 μ

m.

18. A system as defined in claim 11, wherein the pixels of the spatial light modulator each have a response time of less than 2 ms.

19. A system as defined in claim 11, wherein the system produces a full color image with the single spatial light modulator by sequentially producing images of three different

20. A method for displaying-gray scale image frames, comprising

providing a spatial light modulator arranged in an array of pixels, the pixels being switchable into either of two optical states in response to differing applied electric fields;

providing a light source of substantially constant brightness;

dividing the image frame into a plurality of subframes of equal time duration; and

during each frame, switching each pixel to its ON state for a fraction of the subframes proportional to the gray level to be displayed and into its OFF state during the remaining subframes.

21. A method as defined in claim 20, wherein the spatial light modulator is a microdisplay.

22. A method as defined in claim 21, wherein the spatial light modulator is embodied on a silicon substrate.

23. A method as defined in claim 22, wherein adjacent pixels in the spatial light modulator have a pitch of 10 μ

m or less.

24. A method as defined in claim 20, wherein the spatial light modulator reflects light from the light source to produce an overall pattern of gray scale light.

25. A method as defined in claim 20, wherein each pixel has a pixel electrode associated therewith, and the data writing arrangement causes the pixel electrodes to switch to one of two different voltage levels that differ by an amount less than 26 volts.

26. A method as defined in claim 20, wherein the spatial light modulator includes liquid crystal material.

27. A method as defined in claim 26, wherein the liquid crystal material has a thickness of less than 2 μ

m.

28. A method as defined in claim 20, wherein the pixels of the spatial light modulator each have a response time of less than 2 ms.

29. A method as defined in claim 20, wherein a full color image is produced with the single spatial light modulator by sequentially producing images of three different colors.

30. A method for displaying gray scale image frames, comprising

providing a spatial light modulator arranged in an array of pixels, the pixels being switchable into either of two optical states in response to differing applied electric fields, each pixel having a separate pixel electrode associated therewith;

dividing the image frame into a plurality of subframes of equal time duration; and

during each image frame, switching each pixel to its ON state for a fraction of the subframes related to the gray level to be displayed and into its OFF state during the remaining subframes;

wherein the pixel electrodes are switched to one of two different voltage levels to achieve the ON state or the OFF state, the two different voltage levels differing by an amount less than or equal to 5 volts.

31. A method as defined in claim 30, wherein the spatial light modulator is a microdisplay.

32. A method as defined in claim 31, wherein the spatial light modulator is embodied on a silicon substrate.

33. A method as defined in claim 32, wherein adjacent pixels in the spatial light modulator have a pitch of 10 μ

m or less.

34. A method as defined in claim 30, wherein the spatial light modulator reflects light from the light source to produce as an overall pattern of gray scale light.

35. A method as defined in claim 30, wherein the spatial light modulator includes liquid crystal material.

36. A method as defined in claim 35, wherein the liquid crystal material has a thickness of less than 2 μ

m.

37. A method as defined in claim 30, wherein the pixels of the spatial light modulator each have a response time of less than 2 ms.

38. A method as defined in claim 30, wherein a full color image is produced with the single spatial light modulator by sequentially producing images of three different colors.