Monochrome and color digital display systems and methods for implementing the same

• US 6,756,976 B2
• Filed: 03/22/2002
• Issued: 06/29/2004
• Est. Priority Date: 05/03/2000
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Richards, Peter W.
• Primary Examiner(s): Tran, Henry N.
• Application Number:
  US10/104,112
• Publication Number:
  US 20020145585A1
• Time in Patent Office: 830 Days
• Field of Search: 345/204-206, 345/87, 345/690-694, 345/90, 345/531, 345/545, 345/558, 353/20, 353/80, 348/742, 348/744
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0275 Details of drivers for data electrodes, other than drivers for liquid crystal, plasma or OLED displays, not related to handling digital grey scale data or to communication of data to the pixels by means of a current
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/2029 the sub-frames having non-binary weights
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833

Abstract

Methods and apparatus for producing a pulse-width-modulated (PWM) grayscale or color image using a binary spatial light modulator. By staggering and re-quantizing the PWM intervals to a clock of a period based on the frame time divided by number of rows in the display, the system'"'"'s peak bandwidth requirements are optimized for displays of arbitrary resolution and arbitrary choice of PWM waveform. Additionally, a gating circuit increases the optical efficiency of a spatial light modulator using this PWM method in a field-sequential color system by reducing the duration of the blanking period between color fields.

Claims

1. A spatial light modulator (SLM) comprising:

an array of pixel elements;

an array of memory cells coupled to the array of pixel elements, wherein each memory cell controls the state of one of the pixel elements; and

a blanking signal source, coupled to the pixel elements, for simultaneously forcing all pixel elements to an off state in response to a blanking signal without clearing the content of the memory cells.

2. The SLM of claim 1, wherein the blanking signal source includes:

a plurality of gating circuits, each gating circuit being coupled to one of the pixel elements;

a signal line coupled to each gating circuit for simultaneously applying the blanking signal to each gating circuit.

3. The SLM of claim 1, wherein the blanking signal source includes a switching circuit coupled to each of the pixel elements for providing a bias voltage to the pixel elements, wherein when the bias voltage is at a first level the state of each pixel is controlled by the control voltage from the respective memory cell, and wherein when the bias voltage is at a second level the pixel elements are in an off state, wherein when the blanking signal is applied to the switching circuit, the switching circuit switches to the bias voltage such that the pixel elements are simultaneously forced to the off state.

4. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes, each bitplane having a corresponding bitplane weighting, and each bitplane weighting corresponds to a waveform segment duration;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein the stagger intervals are not an integer multiple of the shortest waveform segment duration.

5. The method of claim 4, wherein the subset of pixels is a row or column in a pixel array made up of said plurality of pixels.

6. The method of claim 5, wherein the updating of the row or column is in a spatially sequential order.

7. The method of claim 5, wherein the updating of the row or column is in a spatially non-sequential order.

8. The method of claim 5, wherein the updating of the row or column is in a random or interleaved order.

9. The method of claim 5, wherein the stagger interval has a duration equal to the frame duration divided by the number of the plurality of rows.

10. The method of claim 4, wherein the subintervals between subsequent update events are irregular during each stagger interval.

11. The method of claim 4, further including the step of altering the pixel waveform segment durations such that the update events are distributed at equal subintervals during each stagger interval.

12. The method of claim 4, wherein the step of providing pixels with pixel data includes the steps of storing the image data signals in a buffer over a slow bus, and updating the spatial light modulator with the buffered data signals at the irregular subintervals over a fast bus coupling the buffer to the spatial light modulator.

13. The method of claim 12, wherein the buffer and the spatial light modulator are integrated on the same IC chip.

14. The method of claim 4, wherein the stagger interval is less than the least significant bit.

15. The method of claim 14, wherein the asymmetric updatings are subsequently requantized to make them uniform across the stagger interval.

16. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein the updatings within the corresponding stagger interval are irregularly distributed within the stagger interval.

17. A method for displaying an image comprising a plurality of bitplanes, each bitplane having a bitplane weighting, the method comprising:

displaying a plurality of frames on a spatial light modulator having a plurality of pixels;

wherein during a frame of the plurality of frames, a pixel is updated at a plurality of update events, each of the update events corresponding to a bitplane of the image;

wherein the update events are temporally separated by a plurality of bitplane durations, the bitplane durations being proportional to the bitplane weightings;

wherein the plurality of bitplane durations has a shortest bitplane duration; and

wherein a bitplane duration of the plurality of bitplane durations is not an integer multiple of the shortest bitplane duration.

18. A spatial light modulator comprising

an array of light modulating pixels;

an external data bus;

a FIFO buffer between the external data bus and the array of light modulating pixels;

wherein the FIFO buffer is of a size sufficient to store N rows, where N is the number of bitplanes in the image to be displayed;

and wherein the bus is capable of loading rows of pixel data into said FIFO buffer during a stagger interval, and wherein the FIFO buffer is capable of subsequently loading the rows of pixel data into the array of light modulating pixels at an irregular rate during the stagger interval.

19. A spatial light modulator comprising

an array of light modulating pixels;

an external data bus; and

a FIFO Buffer between the external data bus and the array of light modulating pixels;

wherein the FIFO buffer is constructed so as to allow data to be loaded from an external controller via said external data bus into the FIFO buffer at a constant rate within each stagger interval, and constructed so as to allow data loading from the FIFO buffer to the array of light modulating pixels at an irregular rate.

20. A method for displaying an image comprising;

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein said pixel data is stored in a buffer via a first bus, and wherein the subsets of the plurality of pixels are updated with the pixel data stored in the buffer via a second bus coupling the buffer to the plurality of pixels; and

wherein the subintervals are irregular within the stagger intervals, and the data signals from the buffer are provided to each subset of pixels at irregular subintervals.

21. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein said pixel data is stored in a buffer via a first bus, and

wherein the subsets of the plurality of pixels are updated with the pixel data stored in the buffer via a second bus coupling the buffer to the plurality of pixels; and

wherein the updating with pixel data in the first bus is slower than that in the second bus.

22. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein the average number of pixel subsets that are updated within the stagger intervals is greater than or equal to the bit depth.

23. A method comprising,

providing a pulse width modulation waveform to drive a plurality of pixels in a spatial light modulator;

the waveform comprising repeating frame durations within which the waveform is modulated on and off for a plurality of frame segments of predetermined durations within a frame;

wherein a frame segment having the shortest length in time is a least significant bit;

wherein the plurality of pixels is made up of a plurality of pixel subsets, where the waveform is staggered by a stagger interval between pixel subsets; and

wherein the stagger interval is not equal to an integer multiple of the least significant bit duration.

24. The method of claim 23, wherein the frame segments having lengths greater than the least significant bit are power-of-2 multiples of the least significant bit.

25. The method of claim 23, wherein the number of frame segments is at least eight, and the number of possible grayscale levels is at least 256.

26. The method of claim 23, wherein the stagger interval is not an integer multiple of the least significant bit.

27. The method of claim 23, that achieves 100% bandwidth efficiency.

28. The method of claim 23, wherein the number of grayscale levels is independent of the number of rows.

29. The method of claim 23, wherein the pulse width modulation waveform is independent of logical to physical row mapping.

30. The method of claim 29, wherein the FIFO buffer has a capacity at least equal to the number of bits in a row times a number of update events in a stagger interval.

31. The method of claim 23, wherein a FIFO buffer is provided.

32. The method of claim 23, wherein the pixel subsets are rows in the spatial light modulator.

33. The method of claim 32, wherein an order for updating rows is a spatially sequential order.

34. The method of claim 32, wherein an order for updating rows is a spatially non-sequential order.

35. The method of claim 32, wherein an order for updating rows is one of a random order and an interleaved order.

36. The method of claim 32, wherein each stagger interval is subdivided into a plurality of subintervals, and during each subinterval, a subset of said plurality of pixels is updated with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes.

37. The method of claim 36, wherein the subintervals between subsequent update events are irregular during each stagger interval.

38. The method of claim 37, further including the step of altering the waveform frame segment durations such that the update events are distributed at equal subintervals during each stagger interval.

39. The method of claim 36, wherein the updating of the pixels is based on a video signal source.

40. The method of claim 39, wherein the video signal source is a television tuner, MPEG decoder, video disc player, video tape player or PC graphics card.

41. The method of claim 39, further comprising a video conversion circuit for converting a video signal from the video signal source to digital RGB pixel data.

42. The method of claim 23, further comprising a FIFO buffer, and wherein the buffer and the SLM are integrated on the same IC chip.

43. The method of claim 23, wherein the waveform frame segment durations are binary-weighted.

44. The method of claim 23, wherein the waveform frame segment durations are non-binary-weighted.

45. The method of claim 23, wherein the stagger interval has a duration equal to the frame duration divided by the number of pixel subsets.

46. The method of claim 23, wherein the waveform frame segment duration is different for each of the plurality of bitplanes.

47. A method for operating a spatial light modulator (SLM) comprising:

providing a spatial light modulator having an array of pixel elements and an array of memory cells coupled to the array of pixel elements, wherein each memory cell controls the state of one of the pixel elements;

providing a blanking signal during a blanking interval to the pixel elements to simultaneously force all pixel elements to an off state; and

preloading the spatial light modulator with data during the blanking interval, wherein the blanking signal is provided by a plurality of gating circuits, each gating circuit being coupled to one of the pixel elements; and

a signal line coupled to each gating circuit for simultaneously applying the blanking signal to each gating circuit.

48. A method for operating a spatial light modulator (SLM) comprising:

providing a spatial light modulator having an array of pixel elements and an array of memory cells coupled to the array of pixel elements, wherein each memory cell controls the state of one of the pixel elements;

providing a blanking signal during a blanking interval to the pixel elements to simultaneously force all pixel elements to an off state; and

preloading the spatial light modulator with data during the blanking interval, wherein the blanking signal is provided by a switching circuit coupled to each of the pixel elements for providing a bias voltage to the pixel elements, wherein when the bias voltage is at a first level the state of each pixel is controlled by the control voltage from the respective memory cell, and wherein when the bias voltage is at a second level the pixel elements are in an off state, wherein when the blanking signal is applied to the switching circuit, the switching circuit switches to the bias voltage such that the pixel elements are simultaneously forced to the off state.

49. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a row or column of said plurality of pixels with pixel corresponding to the row or column of pixels and a bitplane of the plurality of bitplanes;

wherein the updating of the row or column is in a spatially non-sequential order.

50. A method for displaying an image comprising:

providing a spatial light modulator having a plurality of pixels;

displaying a plurality of frames on the spatial light modulator, each frame comprising a plurality of bitplanes, each bitplane having a corresponding bitplane weighting, and each bitplane weighting corresponds to a waveform segment duration;

subdividing each frame into a plurality of stagger intervals;

subdividing each stagger interval into a plurality of subintervals;

during each subinterval, updating a subset of said plurality of pixels with pixel data corresponding to the subset of pixels and a bitplane of the plurality of bitplanes;

wherein, during a frame, a subset of said plurality of pixels is updated at a sequence of subset update events, and

wherein the ordering of bitplanes of the update events in a subinterval is different than the ordering of bitplanes of the update events of said subset of pixels during a frame.