Active matrix liquid crystal image generator with hybrid writing scheme

• US 6,317,112 B1
• Filed: 03/20/1998
• Issued: 11/13/2001
• 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: Morrison, Bryan T., Handschy, Mark A., Meadows, Michael R.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Anyaso, Uchendu O.
• Application Number:
  US09/045,253
• Time in Patent Office: 1,334 Days
• Field of Search: 345/89, 345/87, 345/67, 345/76, 345/102, 345/97, 345/92, 345/90, 345/88, 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 a certain gray scale level capability during a given period of time, the given period of time being made up of a plurality of time segments, the system comprising:

a spatial light modulator including an array of light modulating pixels switchable between different light modulating states so as to act on light in different ways;

an illuminator that, during one portion of the time period, directs light of a first intensity into the spatial light modulator during each of a plurality of time segments having different durations of time and, during an other portion of the time period, directs light of different intensity than the first intensity into the spatial light modulator during at least one other time segment; and

a switching arrangement that switches the pixels to desired light modulating states for each time segment of the period of time;

wherein light is directed into the spatial light modulator without substantial interruption during two consecutive time segments in the time period.

2. A system as defined in claim 1, wherein directing light into the spatial light modulator without substantial interruption occurs during the one portion of the time period.

3. A system as defined in claim 1, wherein the light of different intensity than the first intensity is lower in intensity than the first intensity.

4. A system as defined in claim 1, wherein the light of different intensity than the first intensity is light of a plurality of different intensities, one different intensity for each time segment during the other portion of time.

5. A system as defined in claim 4, wherein each time segment in the other portion of the time period is substantially equal in length.

6. A system as defined in claim 5, wherein each of the plurality of different intensities are approximately twice the intensity of the next lower intensity and approximately half the intensity of the next higher intensity.

7. A system as defined in claim 1, wherein the spatial light modulator is arranged as a two-dimensional array of individual pixels.

8. A system as defined in claim 1, wherein each pixel of the spatial light modulator has substantially only two different light modulating states.

9. A system as defined in claim 1, wherein a modulating signal applied to each pixel has substantially only two different signal levels.

10. A system as defined in claim 1, wherein each time segment in the one portion of the time period is approximately twice the length of the next shorter time segment and approximately half the length of the next longer time segment.

11. A system as defined in claim 1, wherein the illuminator includes an LED.

12. A system as defined in claim 11, wherein the illuminator includes three LEDs, each emitting light of a substantially different wavelength than the other LEDs.

13. A system for producing modulated light having a certain gray scale level capability during a given period of time, the given period of time being made up of a plurality of time segments, the system comprising:

a spatial light modulator including an array of light modulating pixels switchable between different light modulating states so as to act on light in different ways;

an illuminator that directs light into the spatial light modulator; and

a switching arrangement that switches the pixels to desired light modulating states for each time segment of the period of time, the switching of the pixels to desired light modulating states not occurring at times other than the beginning and end of each time segment;

wherein the modulated light produced by each pixel has an optical energy that is determined by a combination of the light modulating state of the pixel and the intensity and duration of the light directed into the spatial light modulator, and

further wherein there are two different portions of the time period, one portion in which the illuminator directs light in a substantially continuous manner at a substantially constant intensity while the light modulating state of the pixel is varied for a series of time segments having different lengths, and another portion in which the light modulating state of the pixel is varied for one or more time segments while the illuminator is varied in at least one of intensity level and time duration.

14. A system as defined in claim 13, wherein directing light into the spatial light modulator without substantial interruption occurs during the one portion of the time period.

15. A system as defined in claim 13, wherein the light of different intensity than the first intensity is lower in intensity than the first intensity.

16. A system as defined in claim 13, wherein the light of different intensity than the first intensity is light of a plurality of different intensities, one different intensity for each time segment during the other portion of time.

17. A system as defined in claim 16, wherein each time segment in the other portion of the time period is substantially equal in length.

18. A system as defined in claim 17, wherein each of the plurality of different intensities are approximately twice the intensity of the next lower intensity and approximately half the intensity of the next higher intensity.

19. A system as defined in claim 13, wherein the spatial light modulator is arranged as a two-dimensional array of individual pixels.

20. A system as defined in claim 13, wherein each pixel of the spatial light modulator has substantially only two different light modulating states.

21. A system as defined in claim 13, wherein a modulating signal applied to each pixel has substantially only two different signal levels.

22. A system as defined in claim 13, wherein each time segment in the one portion of the time period is approximately twice the length of the next shorter time segment and approximately half the length of the next longer time segment.

23. A system as defined in claim 13, wherein the illuminator includes an LED.

24. A system as defined in claim 23, wherein the illuminator includes three LEDs, each emitting light of a substantially different wavelength than the other LEDs.

25. A method for producing modulated light, the method comprising:

receiving a number representing a desired level of modulated light, the number being expressed in binary bits of various significance;

sequentially writing the bits during a time period to a light modulator which switches to one of a first light modulating state and a second light modulating state according to the value of the bit, and to one of a first operational mode and a second operational mode according to the significance of the bit; and

illuminating the light modulator with illumination light to produce modulated light therefrom;

wherein the illumination light is of a first intensity level while the light modulator is in the first operational mode for one group of the binary bits, including at least two of the binary bits;

wherein the illumination light is not of the first intensity level while the light modulator is in the second operational mode for the remaining bits that are not in the one group, and further wherein, for each of those remaining bits, the intensity level of the illumination light multiplied by the time duration that the light modulator is in a particular light modulating state while being illuminated is related to the binary significance of the bit; and

wherein when the light modulator is in the first operational mode, the bits of the one group are written without substantially interrupting the illumination of the light modulator.