Active matrix liquid crystal image generator with hybrid writing scheme

• US 5,757,348 A
• Filed: 12/22/1994
• Issued: 05/26/1998
• Est. Priority Date: 12/22/1994
• Status: Expired due to Term

• Current Assignee: Citizen Finetech Miyota Company Limited (Citizen Electronics Company Limited)
• Original Assignee: DT FLCO, Inc. (Micron Technology, Inc.)
• Inventors: Handschy, Mark A., Meadows, Michael R., Morrison, Bryan T.
• Primary Examiner(s): Tung, Kee M.
• Assistant Examiner(s): Suraci, John
• Application Number:
  US08/361,965
• Time in Patent Office: 1,251 Days
• Field of Search: 345/89, 345/67, 345/76, 345/102, 345/97, 345/92, 345/90, 345/88, 345/87, 345/84, 345/55, 359/59
• US Class Current: 345/89
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/063 Waveforms for resetting the whole screen at once
• 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 3/2018 by time modulation using two or more time intervals
• 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 3/2081 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 and method for producing spatially modulated monochrome or color light having gray scale during a given period of time includes a spatial light modulator having a light modulating arrangement switchable between different states so as to act on light in different ways. A switching arrangement switches the modulating arrangement between different states in a controlled way during the period. The system also includes an illumination arrangement for selectively and alternately directing light of constant intensity and varying intensity into the modulating arrangement during predetermined subperiods of the period. In a color version of the system, the illumination arrangement directs light of different colors into the modulating arrangement during predetermined subperiods of the period, thereby providing a system for producing modulated colored light having color gray scale during a given period. In one embodiment of the present invention, the predetermined subperiods include a first plurality of subperiods of unequal lengths of time which, if arranged in order timewise, increase in duration by a factor of two. The predetermined subperiods further include a second plurality of subperiods and the illumination arrangement directs light of variable intensities into the modulator arrangement during each of the second plurality of subperiods which are of equal durations. Each of the different intensities of light double from subperiod to subperiod when the subperiods of equal length are arranged in a particular order.

Claims

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

(a) an active matrix liquid crystal spatial light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material which is designed to switch between ON and OFF states, said layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns and

(ii) active matrix means including VLSI circuitry for dividing said layer of liquid crystal material into an array of individual liquid crystal pixels and for causing each of said pixels of liquid crystal material to modulate light individually by switching between said ON and OFF states in a way that depends upon the manner in which the VLSI circuitry is written, said VLSI circuitry of said active matrix means including an array of subcircuits, each of which is dedicated to and defines a specific one of said pixels;

(b) illumination means including a light source for directing light from said source into said pixel-divided layer of ferroelectric liquid crystal material in a specific way; and

(c) means for writing said VLSI circuitry with preselected data in accordance with a particular data ordering scheme such that said circuitry, in response to the data, causes said pixels of liquid crystal material to individually switch between their ON and OFF states and therefore modulate light from said source in a way which, depending upon said data, produces a specific overall pattern of gray scale light; and

wherein

(i) said particular data ordering scheme is such that said data writing means writes each of said subcircuits and therefore each of said pixels with preselected data in a predetermined successive order, timewise, so that none of said subcircuits includes buffer circuitry thereby reducing the complexity of said array of subcircuits

(ii) said preselected data is digital data divided into individual digital data commands, one for each of said subcircuits and therefore each of said pixels, each digital data command establishing, during any given time frame, the length of time its associated pixel is in its ON and OFF state during a given time frame, each of said given time frames being divided into a first plurality of subframes and a second plurality of subframes for purposes of obtaining gray scale,

(iii) said illumination means includes means for maintaining the intensity of light directed from said light source into said pixel-divided layer of liquid crystal material substantially constant during said first plurality of subframes and means for directing light of variable intensities from said light source into said pixel-divided layer of liquid crystal material during said second plurality of subframes, and

(iv) each of said digital data commands establishes whether its associated pixel is in its ON or OFF state during each subframe of any given frame.

2. A system according to claim 1 wherein said first plurality of subframes is a plurality of subframes of unequal lengths of time.

3. A system according to claim 2 wherein the durations of the subframes of said first plurality of subframes, if arranged in order of duration, increase by a factor of two.

4. A system according to claim 1 wherein said means for directing light of variable intensities directs light of different intensities into said pixel-divided layer during each of said second plurality of subframes of any given frame, whereby whether any given pixel is in its ON or OFF state during the various subframes of a given time frame determines the overall gray scale of that pixel during that time frame.

5. A system according to claim 4 wherein said second plurality of subframes is a plurality of subframes of equal lengths of time.

6. A system according to claim 5 wherein each of said different intensities of light double from subframe to subframe when said subframes of equal length are arranged in order of intensity of light.

7. A system according to claim 1 wherein each of said digital data commands comprises a series of binary bits, one bit for each of said subframes, each binary bit establishing whether its associated pixel is in its ON or OFF state during its associated subframe.

8. A system according to claim 1 wherein;

(a) said first plurality of subframes is a plurality of subframes of unequal lengths of time;

(b) said second plurality of subframes is a plurality of subframes of equal lengths of time;

(c) the shortest subframe, timewise, of said first plurality of subframes is twice the length of time of said second plurality of subframes of equal lengths of time; and

(d) said means for directing light of variable intensities into said pixel-divided layer during said second plurality of subframes reduces the intensity of said light by one half for each of the subframes of said second plurality of subframes.

9. A system according to claim 1 wherein each of said frames includes an additional blackout subframe after each of said second plurality of subframes of equal time periods and wherein each of said digital data commands includes a binary bit associated with each of said blackout subframes for maintaining its associated pixel in an OFF state during its associated blackout subframe, each of said blackout subframes being sufficiently long to allow all of the pixels written during each immediately previous subframe of equal time period to respond fully and to allow said illumination means to switch the intensity of said light source before the writing means begins writing the pixels in the next subframe.

10. A system for producing modulated color light having color gray scale, said system comprising:

(a) an active matrix liquid crystal spatial light modulator having

(i) light modulating means including 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 said layer of liquid crystal material into an array of individual liquid crystal pixels and for causing each of said pixels of liquid crystal material to modulate light individually by switching between said ON and OFF states in a way that depends upon the manner in which the VLSI circuitry is written, said VLSI circuitry of said active matrix means including an array of subcircuits, each of which is dedicated to and defines a specific one of said pixels;

(b) illumination means including a light source for directing light of different colors from said source into said pixel-divided layer of ferroelectric liquid crystal material in a specific way; and

(c) means for writing said VLSI circuitry with preselected data in accordance with a particular data ordering scheme such that said circuitry, in response to the data, causes said pixels of liquid crystal material to individually switch between their ON and OFF states and therefore modulate light from said source in a way which, depending upon said data, produces a specific overall pattern of color gray scale light; and

wherein

(i) said particular data ordering scheme in such that said data writing means writes each of said subcircuits and therefore each of said pixels with preselected data in a predetermined successive order, timewise, so that none of said subcircuits includes buffer circuitry, thereby reducing the complexity of said array of subcircuits;

(ii) said preselected data is digital data divided into individual digital data commands, one for each of said subcircuits and therefore each of said pixels, each digital data command establishing, during any given time frame, the length of time its associated pixel is in its ON and OFF state during a given time frame, each of said given time frames being divided into a plurality of color subframes for purposes of obtaining color, and each of said color subframes being divided into a first plurality of sub-subframes and a second plurality of sub-subframes for purposes of obtaining color gray scale,

(iii) said illumination means includes means for alternatively directing light of different colors, equal in number to the number of said color subframes, into said pixel-divided layer of liquid crystal material during each successive color subframe of each frame and said illumination means including means for maintaining the intensity of light directed from said light source into said pixel-divided layer of liquid crystal material substantially constant during said first plurality of sub-subframes and means for directing light of variable intensities from said light source into said pixel-divided layer of liquid crystal material during said second plurality of sub-subframes, and

(iv) each of said digital data commands establishes whether its associated pixel is in its ON or OFF state during each sub-subframe of any given frame.

11. A system according to claim 10 wherein said first plurality of sub-subframes is a plurality of sub-subframes of unequal lengths of time.

12. A system according to claim 11 wherein the durations of the subframes of said first plurality of subframes, if arranged in order of duration, increase by a factor of two.

13. A system according to claim 10 wherein said means for directing light of variable intensities directs light of different intensities into said pixel-divided layer during each of said second plurality of sub-subframes of any given frame, whereby whether any given pixel is in its ON or OFF state during the various sub-subframes of a given time frame determines the overall color gray scale of that pixel during that time frame.

14. A system according to claim 13 wherein said second plurality of sub-subframes is a plurality of sub-subframes of equal lengths of time.

15. A system according to claim 14 wherein each of said different intensities of light double from sub-subframe to sub-subframe when said sub-subframes of equal length are arranged in order of intensity of light.

16. A system according to claim 10 wherein each of said digital data commands comprises a series of binary bits, one bit for each of said sub-subframes, each binary bit establishing whether its associated pixel is in its ON or OFF state during its associated sub-subframe.

17. A system according to claim 10 wherein;

(a) said first plurality of sub-subframes is a plurality of sub-subframes of unequal lengths of time;

(b) said second plurality of sub-subframes is a plurality of sub-subframes of equal lengths of time;

(c) the shortest sub-subframe, timewise, of said first plurality of sub-subframes is twice the length of time of said second plurality of sub-subframes of equal lengths of time; and

(d) said means for directing light of variable intensities into said pixel-divided layer during said second plurality of sub-subframes reduces the intensity of said light by one half for each of the sub-subframes of said second plurality of sub-subframes.

18. A system according to claim 10 wherein each of said frames includes an additional blackout sub-subframe after each of said second sub-subframes of equal time periods and wherein each of said digital data commands includes a binary bit associated with each of said blackout sub-subframes for maintaining its associated pixel in an OFF state during its associated blackout sub-subframe, each of said blackout sub-subframes being sufficiently long to allow all of the pixels written during each immediately previous sub-subframe of equal time period to respond fully and to allow said illumination means to switch the intensity of said light source before the writing means begins writing the pixels in the next sub-subframe of equal time period.

19. A system according to claim 18 wherein each of said color subframes includes an additional blackout subframe after each of said color subframes and wherein each of said digital data commands includes a binary bit associated with each of said blackout subframes for maintaining its associated pixel in an OFF state during its associated blackout subframe, each of said blackout subframes being sufficiently long to allow all of the pixels written during each immediately previous color subframe to respond fully and to allow said illumination means to switch colors before the writing means begins writing the pixels in the next color subframe.

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

(a) an active matrix liquid crystal spatial light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material which is designed to switch between ON and OFF states, said layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns; and

(ii) active matrix means including VLSI circuitry for dividing said layer of liquid crystal material into a rectangular array of immediately adjacent liquid crystal pixels, each of which has a maximum light modulating area of at most approximately 100 square microns, and for causing each of said pixels of liquid crystal material to modulate light individually by switching between said ON and OFF states in a way that depends upon the manner in which the VLSI circuitry is written, said VLSI circuitry including an array of subcircuits, each of which is dedicated to and defines a specific one of said pixels, each of said subcircuits including one and only one active component for modulating its associated pixel, whereby to reduce the space required by each subcircuit and thereby reduce the size of each of said pixels;

(b) illumination means including a light source consisting of light emitting diode means for directing light from said source into said pixel-divided layer of ferroelectric liquid crystal material in a specific way; and

(c) means for writing said VLSI circuitry with preselected data in accordance with a particular data ordering scheme such that said circuitry in response to the data, causes said pixels of liquid crystal material to individually switch between their ON and OFF states and therefore modulate light from said source in a way which, depending upon said data, produces a specific overall pattern of gray scale light; and

wherein

(i) said particular data ordering scheme is designed so that said data writing means writes each of said subcircuits and therefore each of said pixels with preselected data in a predetermined successive order, timewise, so that said VLSI circuitry does not require buffer subcircuitry for writing said subcircuits simultaneously, thereby reducing the complexity of said array of subcircuits,

(ii) said preselected digital data is divided into individual digital data commands, one for each of said subcircuits and therefore each of said pixels, during any given time frame, each digital data command establishing the length of time its associated pixel is in its ON and OFF state during a given time frame, each of said given time frames being divided into a first plurality of subframes of unequal time periods and a second plurality of subframes of smaller but equal time periods for purposes of obtaining gray scale,

(iii) said illumination means includes means for maintaining the intensity of light directed from said light source into said pixel-divided layer of liquid crystal material substantially constant during said first plurality of subframes and for directing light of variable intensities from said light source into said pixel-divided layer of liquid crystal material during said second plurality of subframes, and

(iv) each of said digital data commands establishing whether its associated pixel is in its ON or OFF state during each subframe of any given frame.

21. A system according to claim 20 wherein each of said digital commands comprises a series of binary bits, one for each of said subframes, each binary bit establishing whether its associated pixel is in its ON or OFF state during its associated subframe.

22. A system according to claim 21 wherein each of said frames includes an additional blackout subframe after each of said subframes of equal time periods and wherein each of said digital data commands includes a binary bit associated with each of said blackout subframes for maintaining its associated pixel in an OFF state during its associated blackout subframe, each of said blackout subframes being sufficiently long to allow all of the pixels written during each immediately previous subframe to respond fully and to allow said illumination means to switch the intensity of said light source before the writing means begins writing the pixels in the next subframe.

23. A system for producing modulated color light having color gray scale, said system comprising:

(a) an active matrix liquid crystal spatial light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material which is designed to switch between ON and OFF states, said layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns; and

(ii) active matrix means including VLSI circuitry for dividing said layer of liquid crystal material into a rectangular array of immediately adjacent liquid crystal pixels, each of which has a maximum light modulating area of at most approximately 100 square microns, and for causing each of said pixels of liquid crystal material to modulate light individually by switching between said ON and OFF states in a way that depends upon the manner in which the VLSI circuitry is written, said VLSI circuitry including an array of subcircuits, each of which is dedicated to and defines a specific one of said pixels, each of said subcircuits including one and only one active component for modulating its associated pixel, whereby to reduce the space required by each subcircuit and thereby reduce the size of each of said pixels;

(b) illumination means including a light source consisting of light emitting diode means for directing light of different colors from said source into said pixel-divided layer of ferroelectric liquid crystal material in a specific way; and

(c) means for writing said VLSI circuitry with preselected data in accordance with a particular data ordering scheme such that said circuitry, in response to the data, causes said pixels of liquid crystal material to individually switch between their ON and OFF states and therefore modulate light from said source in a way which, depending upon said data, produces a specific overall pattern of color gray scale light; and

wherein

(i) said particular data ordering scheme is designed so that said data writing means writes each of said subcircuits and therefore each of said pixels with preselected data in a predetermined successive order, timewise, so that said VLSI circuitry does not require buffer subcircuitry for writing said subcircuits simultaneously, thereby reducing the complexity of said array of subcircuits,

(ii) said preselected digital data is divided into individual digital data commands, one for each of said subcircuits and therefore each of said pixels, during any given time frame, each digital data command establishing the length of time its associated pixel is in its ON and OFF state during a given time frame, each of said given time frames being divided into color subframes for purposes of obtaining color, said color subframes being divided into a first plurality of sub-subframes of unequal time periods and a second plurality of sub-subframes of smaller but equal time periods for purposes of obtaining color gray scale,

(iii) said illumination means includes means for alternatively directing light of different colors, equal in number to the number of said color subframes, into said pixel-divided layer of liquid crystal material during each successive color subframe of each frame and said illumination means including means for maintaining the intensity of light directed from said light source into said pixel-divided layer of liquid crystal material substantially constant during said first plurality of sub-subframes and for directing light of variable intensities from said light source into said pixel-divided layer of liquid crystal material during said second plurality of sub-subframes, and

(iv) each of said digital data commands establishing whether its associated pixel is in its ON or OFF state during each sub-subframe of any given frame.

24. A system according to claim 23 wherein each of said digital commands comprises a series of binary bits, one for each of said sub-subframes, each binary bit establishing whether its associated pixel is in its ON or OFF state during its associated sub-subframe.

25. A system according to claim 24 wherein each of said frames includes an additional blackout sub-subframe after each of said sub-subframes of equal time periods and wherein each of said digital data commands includes a binary bit associated with each of said blackout sub-subframes for maintaining its associated pixel in an OFF state during its associated blackout sub-subframe, each of said blackout sub-subframes being sufficiently long to allow all of the pixels written during each immediately previous sub-subframe of equal time period to respond fully and to allow said illumination means to switch the intensity of said light source before the writing means begins writing the pixels in the next sub-subframe of equal time period.

26. A display system for producing an active matrix display having a certain frame rate, said system comprising:

a) a spatial light modulator having an array of liquid crystal pixels each of which is adapted to be operated between different light modulating states independently from the others during each of said frames said array of liquid crystal pixels including a layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns;

b) means for selectively controlling the light modulating states of each of said pixels for a controlled portion of time during each of said frames, said frames being divided into a plurality of subframes, said plurality of subframes including a first and a second group of subframes, and during said subframes, each of said pixels has a selected light modulating state; and

c) illumination means including a source of light and means for coupling said light with said spatial light modulator in a way which causes said spatial light modulator to produce a visual display depending upon the light modulating state of the various pixels, said illuminating means including means for coupling a controllable brightness of light with said spatial light modulator for each of said subframes, said controllable brightness being substantially continuous at a substantially constant brightness during said first group of subframes and, during said second group of subframes, said brightness of light being varied from subframe to subframe

whereby said plurality of subframes provide binary control of the gray scale of each of said pixels for each of said frames by selectively controlling the light modulating state of each of said pixels during each of said subframes in combination with selectively controlling said brightness of light during each of said subframes.

27. A system according to claim 26 wherein said first group of subframes is made up of subframes having different lengths of time.

28. A system according to claim 27 wherein said first group of subframes is made up of subframes having different lengths of time such that a longest subframe in said first group of subframes is twice as long as a second longest subframe in said first group of subframes and each of any remaining subframes in said first group of subframes are half as long as their respective next longer subframe in said first group of subframes.

29. A system according to claim 26 wherein said second group of subframes is made up of subframes having equal lengths of time.

30. A system according to claim 29 wherein said second group of subframes is made up of subframes having equal lengths of time which are equal to the length of time of the shortest subframe in said first group of subframes and wherein said brightness of light is varied such that it is the same brightness during a brightest subframe within said second group of subframes as the light is during said first group of subframes and during each of any remaining subframes within said second group of subframes said light is half as bright as it is for the respective next brighter subframe in said second group of subframes.

31. A system for producing modulated light having gray scale during a given period of time comprising;

(a) a spatial light modulator including a layer of liquid crystal light modulating material switchable between different states so as to act on light in different ways, said layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns,

(b) means for switching said modulating means between different states in a controlled way during said period, and

(c) illumination means for selectively and alternately directing light of constant intensity into said modulating means during each of a first plurality of subperiods of said period and for selectively and alternately directing light of a different intensity than said constant intensity into said modulating means during a different subperiod of said period.

32. A system according to claim 31 wherein said illumination means for selectively and alternately directing light of a different intensity than said constant intensity into said modulating means during a different subperiod of said period includes means for selectively and alternately directing light of different intensities than said constant intensity into said modulating means during a second plurality of subperiods of said period.

33. A system according to claim 32 wherein said illumination means directs light of different intensities into said modulator means during each of said second plurality of subperiods.

34. A system according to claim 33 wherein said second plurality of subperiods is a plurality of subperiods of equal lengths of time.

35. A system according to claim 34 wherein each of said different intensities of light double from subperiod to subperiod when said subperiods of equal length are arranged in order of intensity of light.

36. A system according to claim 31 wherein said illumination means directs light of different colors into said modulating means during predetermined subperiods of said period, thereby providing a system for producing modulated colored light having color gray scale during a given period.

37. A system according to claim 31 wherein said first plurality of subperiods is a plurality of subperiods of unequal lengths of time.

38. A system according to claim 37 wherein the durations of the subperiods of said first plurality of subperiods, if arranged in order of duration, increase by a factor of two.

40. A method according to claim 31 wherein the step of causing said illumination means to selectively and alternately direct light of a different intensity than said constant intensity into said modulating means during a different subperiod of said period includes the step of causing said illumination means to selectively and alternately direct light of different intensities than said constant intensity into said modulating means during a second plurality of subperiods of said period.

41. A method according to claim 40 wherein said illumination means directs light of different intensities into said modulator means during each of said second plurality of subperiods.

42. A method according to claim 41 wherein said second plurality of subperiods is a plurality of subperiods of equal lengths of time.

43. A method according to claim 42 wherein each of said different intensities of light double from subperiod to subperiod when said subperiods of equal length are arranged in order of intensity of light.

44. A method according to claim 31 wherein said step of causing said illumination means to selectively and alternately direct light of constant intensity and different intensity into said modulating means includes the step of causing said illumination means to direct light of different colors into said modulating means during predetermined subperiods of said period, thereby providing a system for producing modulated colored light having color gray scale during a given period.

45. A method according to claim 31 wherein said first plurality of subperiods is a plurality of subperiods of unequal lengths of time.

46. A method according to claim 45 wherein the durations of the subperiods of said first plurality of subperiods, if arranged in order of duration, increase by a factor of two.

39. A method for producing modulated light having gray scale during a given period of time comprising the steps of;

(a) providing a spatial light modulator including a layer of liquid crystal light modulating material switchable between different states so as to act on light in different ways, said layer of liquid crystal material having a substantially uniform thickness of at most approximately 2 microns,

(b) switching said modulating means between different states in a controlled way during said period,

(c) providing illumination means, and

(d) causing said illumination means to selectively and alternately direct light of constant intensity into said modulating means during each of a first plurality of subperiods of said period and to selectively and alternately direct light of a different intensity than said constant intensity into said modulating means during a different subperiod of said period.