Active matrix liquid crystal image generator

• US 6,570,550 B1
• Filed: 03/20/1998
• Issued: 05/27/2003
• Est. Priority Date: 12/22/1994
• Status: Expired due to Fees

• 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.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Alphonse, Fritz
• Application Number:
  US09/045,247
• Time in Patent Office: 1,894 Days
• Field of Search: 345/148, 345/89, 345/85, 345/98, 345/6, 345/83, 345/130, 345/108, 345/97, 359/224, 359/230, 359/291, 359/630, 348/743
• 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, the system comprising:

a) a spatial light modulator having an array of pixels switchable between different light modulating states and having a switching arrangement that switches each of the pixels in response to an applied voltage to modulate light individually by switching the pixels between the different light modulating states, the switching arrangement including an array of subcircuits, each subcircuit of which is dedicated to a specific one of the pixels;

b) a light source for directing light into the spatial light modulator; and

c) a data writing arrangement that writes the switching arrangement with preselected data in accordance with a particular data ordering scheme such that the switching arrangement, in response to the data, causes the pixels to individually switch between their different light modulating states and therefore modulate light from the light source in a way which, depending upon the data, produces a specific overall pattern of gray scale light, the particular data ordering scheme being such that the data writing arrangement writes each of the subcircuits, and therefore each of the pixels, with preselected data in a predetermined successive order, timewise;

wherein the voltage applied to the pixel is configured to be at either one of only two different voltage levels; and

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

2. A system according to claim 1 wherein the spatial light modulator is a liquid crystal spatial light modulator including a layer of liquid crystal material switchable between different light modulating states.

3. A system according to claim 2 wherein the layer of liquid crystal material is a layer of ferroelectric liquid crystal material.

4. A method of displaying gray scale or color images, the method comprising the steps of:

(a) providing an array of light modulating pixels organized in certain groups of pixels, each pixel being switchable between only a first pixel state and a second blackout pixel state in response to input data;

(b) switching all of the pixels to the second blackout pixel state;

(c) after all of the pixels have been switched to the second blackout pixel state, illuminating the array of pixels with light of a first desired brightness and color;

(d) while the array of pixels is being illuminated with the desired brightness and color of light, switching the states of the pixels in each of the groups such that the array of pixels forms a desired pattern of modulated light, at least some of the groups of pixels being switched at different times from other ones of the groups;

(e) switching all of the pixels to the second blackout pixel state a second time in such a manner that the time interval between the time at which the states of the pixels in each group are switched to form the desired pattern of modulated light and the time at which that group is switched to the second blackout pixel state the second time is the same for each group of pixels; and

(f) after all of the pixels have been switched to the second blackout pixel state the second time, illuminating the array of pixels with light of a second desired brightness and color.

5. The method according to claim 4 wherein said array of pixels is an active matrix array of pixels including an array of subcircuits, each subcircuit of which array of subcircuits is dedicated to and defines a specific one of said pixels, said array of subcircuits being configured such that none of said subcircuits requires auxiliary data storage buffer circuitry for storing said input data in order to use said input data to switch the states of said pixels and therefore complexity of said array of subcircuits can be reduced.

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

(a) an active matrix liquid crystal light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material, which liquid crystal material is designed to switch between ON and OFF states, and

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

(b) illumination means including a source of light for directing light from said source into said pixel-divided layer of ferroelectric liquid crystal material; 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 ferroelectric 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, said particular data ordering scheme being 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;

wherein the preselected data written to the switching arrangement is configured to be at either one of only two different voltage levels; and

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

7. The system according to claim 6 wherein said preselected data is digital data 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 a length of time its associated pixel is in the ON and OFF state during said given time frame.

8. The system according to claim 7 wherein each of said given time frames is divided into a plurality of subframes for purposes of obtaining gray scale, and wherein 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, whereby whether any given pixel is in its ON or OFF state during the various subframes of that given time frame determines the overall gray scale of that pixel during that given time frame.

9. The system according to claim 8 wherein said plurality of subframes are a plurality of subframes of unequal lengths of time.

10. The system according to claim 9 wherein duration of the subframes, if arranged in order of duration, increases by a factor of two.

11. The system according to claim 8 wherein each of said digital data commands comprises a series of binary bits, one binary bit for each of said subframes, each binary bit establishing whether its associated pixel is in the ON or OFF state during its associated subframe.

12. The system according to claim 7 wherein each of said given time frames is divided into a plurality of subframes for purposes of obtaining color, wherein each of said subframes is divided into a plurality of sub-subframes of predetermined time periods for purposes of obtaining colored gray scale, wherein said illumination means includes means for alternatively directing light of different colors, equal in number to the number of said subframes, into said pixel-divided layer of ferroelectric liquid crystal material during each successive subframe of each frame, and wherein each of said digital data commands establishes whether its associated pixel is in the ON or OFF state during the various subframes and sub-subframes of a given time frame determines the overall gray scale and color of that pixel during that given time frame.

13. The system according to claim 12 wherein each of said digital data commands comprises a series of binary bits, one for each of said sub-subframes, each binary bit establishing whether its associated pixel is in the ON or OFF state during its associated sub-subframe.

14. The system according to claim 13 wherein each of said subframes includes an additional blackout subframe after each of said first-mentioned 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 the 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 colors before the writing means begins writing the pixels in the next subframe.

15. The system according to claim 6 wherein each of said subcircuits includes one and only one active component for modulating its associated pixel.

16. The system according to claim 6 wherein said illumination means including said light source further includes means for directing light of different colors into said pixel-divided layer of ferroelectric liquid crystal material in a specific way so as to produce modulated colored light having gray scale and a polarizer/analyzer designed to pass light across a broad color band including light of different colors.

17. The system according to claim 6 wherein said illumination means includes at least one light emitting diode serving as said light source.

18. The system according to claim 17 wherein said light emitting diode is the sole source of light of said illumination means.

19. The system according to claim 18 wherein said illumination means includes at least three light emitting diodes serving as said light source, each of which light emitting diodes is a different color from others.

20. The system according to claim 19 wherein said light emitting diodes include red, green and blue light emitting diodes.

21. The system according to claim 6 further comprising means for viewing said light modulated by said layer of ferroelectric liquid crystal material, whereby said system serves as a light display.

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

(a) an active matrix liquid crystal light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material, which liquid crystal material is designed to switch between ON and OFF states, and

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

(b) illumination means including a source of light for directing light from said source into said pixel-divided layer of ferroelectric liquid crystal material; 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 ferroelectric 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, said particular data ordering scheme being 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;

wherein the preselected data written to the switching arrangement is configured to be at either one of only two different voltage levels; and

further wherein each pixel of said array of immediately adjacent pixels has a maximum light modulating area of at most 100 square microns.

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

(a) an active matrix liquid crystal light modulator having

(i) light modulating means including a layer of ferroelectric liquid crystal material, which liquid crystal material is designed to switch between ON and OFF states, and

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

(b) illumination means including a source of light for directing light from said source into said pixel-divided layer of ferroelectric liquid crystal material; 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 ferroelectric 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, said particular data ordering scheme being 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;

wherein the preselected data written to the switching arrangement is configured to be at either one of only two different voltage levels; and

further wherein each of said pixels is square shaped, at most 10 microns on a side.

24. 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 to switch to one of only two different voltage levels that differ by about 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.

25. 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, wherein the light modulation between the two optical states is achieved without substantial mechanical motion;

a light source; 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.

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

a reflective spatial light modulator having an array of rows of pixels switchable between different light modulating states;

a light source; and

a data writing arrangement that writes data to the pixels of the spatial light modulator, 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;

wherein the pitch of each row of pixels is less than 10 μ

m.

27. A system for producing modulated light having gray scale for each of a plurality of different colors, the system comprising:

a spatial light modulator having an array of pixels switchable between different light modulating states, wherein the light modulation between the light modulating states is achieved without substantial mechanical motion;

a light source arrangement that can selectively illuminate the spatial light modulator with the plurality of different colors; and

a data writing arrangement that writes image data to the pixels of the spatial light modulator for each of a series of frames of video data, each frame including a plurality of color subframes 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;

wherein the image data written to each particular pixel is changed multiple times within each color subframe in a manner that changes the gray scale during that color subframe.

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

a reflective spatial light modulator arranged on a silicon substrate, the SLM having an array of pixels switchable between different light modulating states, each pixel having a pixel electrode;

a light source; and

a data writing arrangement that writes data to the pixels, to cause the pixel electrodes to switch to one of only two different voltage levels that differ by about 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.

29. A liquid crystal spatial light modulator having gray scale, for use in cooperation with a light source, comprising:

an array of pixels, each pixel having a plurality of discrete electrical states;

a portion of liquid crystal material associated with each pixel, the liquid crystal material having a plurality of optical states, each portion of liquid crystal material responding optically in a substantially uniform manner to each particular electrical state of its associated pixel; and

a data writing arrangement that writes gray scale image data to the array of pixels;

wherein the image data is arranged into frames of image data, each frame representing an image, and wherein the data writing arrangement can cause any pixel to be in different electrical states during a particular frame, the combination of the electrical states of each pixel representing a gray scale intensity such that the array of pixels, in cooperation with the light source and the liquid crystal material, produces a gray scale image during a frame; and

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

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

a) a spatial light modulator having an array of pixels switchable between different light modulating states and having a switching arrangement that switches each of the pixels to modulate light individually by switching the pixels between the different light modulating states, the switching arrangement including an array of subcircuits, each subcircuit of which is dedicated to a specific one of the pixels;

b) a light source for directing light into the spatial light modulator; and

c) a data writing arrangement that writes the switching arrangement with preselected data in accordance with a particular data ordering scheme such that the switching arrangement, in response to the data, causes the pixels to individually switch between their different light modulating states and therefore modulate light from the light source in a way which, depending upon the data, produces a specific overall pattern of gray scale light, the particular data ordering scheme being such that the data writing arrangement writes each of the subcircuits, and therefore each of the pixels, with preselected data in a predetermined successive order, timewise;

wherein the preselected data written to the switching arrangement is configured to be at either one of only two different voltage levels; and

further wherein none of the subcircuits require auxiliary data storage buffer circuitry.