Monochrome and color digital display systems and methods

• US 6,388,661 B1
• Filed: 05/03/2000
• Issued: 05/14/2002
• Est. Priority Date: 05/03/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Richards, Peter W.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Tran, Henry N.
• Application Number:
  US09/564,069
• Time in Patent Office: 741 Days
• Field of Search: 345/204, 345/87, 345/205, 345/690, 345/691-694, 345/206, 348/742, 348/744, 353/20, 353/80
• 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 and having a plurality of rows, wherein each memory cell controls the state of one of the pixel elements; and

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

wherein when a blanking control signal is applied to the gating circuits, all associated pixel elements are simultaneously forced to an off state regardless of the content of the associated memory cells.

2. The SLM of claim 1, further including a signal line coupled to each gating circuit for simultaneously applying the blanking control signal to each gating circuit.

3. The SLM of claim 2, wherein each gating circuit includes a logical AND gate having a first input terminal coupled to the signal line and a second input terminal coupled to the output of the associated memory cell, and an output terminal coupled to the associated pixel element, wherein when the blanking control signal applied to the AND gates is low, all associated pixel elements are simultaneously forced to the off state.

4. The SLM of claim 2, wherein each gating circuit includes a logical gate selected from the group consisting of an AND gate, an OR gate, a NOR gate and a NAND gate.

5. A spatial light modulator (SLM) comprising:

an array of electrostatic 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 by applying a control voltage to the corresponding pixel element; and

a switching circuit coupled to all of the pixel elements for providing a bias voltage to all 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 all pixel elements are, in an off state,

wherein when a blanking signal is applied to the switching circuit, the switching circuit switches the bias voltage to the second level such that all pixel elements are simultaneously forced to an off state regardless of the applied control voltages.

6. A method of driving a spatial light modulator (SLM) in a field-sequential-color (FSC) display system, wherein the SLM includes an array of memory cells coupled to an array of pixel elements, said array of memory cells comprising a plurality of rows, wherein each memory cell controls the state of one of the pixel elements, wherein the FSC system includes a color generating mechanism capable of illuminating the pixel elements with multiple color fields, the method comprising the steps of:

illuminating the pixel elements with the multiple color fields in a cyclical manner, wherein each color field illuminates the SLM one or more times during a frame;

during each field, selecting the rows of the SLM in an update sequence having a plurality of update events, each update event in said update sequence corresponding to a predetermined row of an image and one of a plurality of predetermined bitplanes of said image, each bitplane having a predetermined pixel waveform segment duration;

providing a plurality of image data signals to the SLM at each update event, such that the selected row of the SLM is updated with image data corresponding to the selected row and bitplane of the image;

between each subsequent color field, blanking all pixel elements for an interval having a predetermined duration; and

during each blanking interval, pre-loading the memory cells of the SLM such that when the blanking interval ends, the next color field'"'"'s update sequence may be resumed in a continuous manner so as to eliminate pixel dead time after the end of the blanking interval.

7. The method of claim 6, wherein the update events for each row are staggered relative to the update events of a previous row in a row order, wherein during each stagger interval a number of update events occur, said number of update events being equal to the number of update events occurring for each row during a frame.

8. The method of claims 7, wherein the stagger interval has a duration equal to the frame duration divided by the number of said plurality of rows.

9. The method of claim 6, wherein the FSC system includes a light source and a color wheel, wherein the step of illuminating the pixels with the multiple color fields in a cyclical manner includes the steps of illuminating the color wheel with the light source and rotating the color wheel such that the color of the illumination incident on the SLM is synchronized with the color field data displayed on the SLM.

10. The method of claim 6, wherein the color fields include a red (R), a green (G) and a blue (B) color field.

11. The method of claim 6, wherein each color field illuminates the pixel array two or more times during a cycle.

12. The method of claim 6, wherein the durations of the color fields are different during a cycle.

13. A method of reducing an amount of flicker perceived by a viewer in a field-sequential color (FSC) system having a spatial light modulator (SLM), wherein the SLM includes an array of memory cells coupled to an array of pixel elements, said memory cell array comprising a plurality of rows, wherein each memory cell controls the state of one of the pixel elements, wherein the FSC system includes a color generating mechanism capable of illuminating the pixel elements with multiple color fields, the method comprising the steps of:

illuminating the pixel elements with the multiple color fields in a cyclical manner, wherein each color field illuminates the SLM two or more times during a frame;

during each field, selecting the rows of the SLM in an update sequence having a plurality of update events, each update event in said update sequence corresponding to a predetermined row of an image and one of a plurality of predetermined bitplanes of said image, each bitplane having a predetermined pixel waveform segment duration;

providing a plurality of image data signals to the SLM at each update event, such that the selected row of the SLM is updated with image data corresponding to the selected row and bitplane of the image;

blanking all pixel elements between each subsequent color field for an interval having a predetermined duration; and

during each blanking interval, preloading the memory cells with data such that when the blanking interval ends, the next color field'"'"'s update sequence may be resumed in a continuous manner so as to reduce the amount of flicker perceived by the viewer.

14. The method of claim 13, wherein the update events for each row are staggered relative to the update events of a previous row in a row order, wherein during each stagger interval a number of update events occurs, said number of update events occurring during each stagger interval being equal to the number of update events occurring for each row during a frame.

15. The method of claim 14, wherein the stagger interval has a duration equal to the frame duration divided by the number of said plurality of rows.

16. The method of claim 13, wherein the FSC system includes a light source and a color wheel, wherein the step of illuminating the pixels with the multiple color fields in a cyclical manner includes the steps of illuminating the color wheel with the light source and rotating the color wheel such that each color field illuminates the pixel array two or more times during a cycle.

17. The method of claim 13, wherein the color fields include a red (R), a green (G) and a blue (B) color field.

18. A method of reducing an amount of color breakup perceived by a viewer in a field-sequential color (FSC) system having a spatial light modulator (SLM) driven by bitplane data signals, wherein the SLM includes an array of memory cells coupled to an array of pixel elements, wherein each memory cell controls the state of one of the pixel elements, wherein the FSC system includes a color generating mechanism capable of illuminating the pixel elements with multiple color fields, the method comprising the steps of:

illuminating the pixel elements with the multiple color fields in a cyclical manner, wherein each color field illuminates the SLM during each cycle;

providing bitplane data signals to the memory cells such that during each color field each of a plurality of rows of memory cells is updated by one or more of a plurality of update bitplanes, each update bitplane having a predetermined weight;

simultaneously blanking all pixel elements one or more times during each separate color field for an interval having a predetermined duration, so as to split each color field into two or more subfields;

simultaneously blanking all pixel elements between each separate color field for said interval having said predetermined duration; and

during each blanking interval, preloading the memory cells with data such that when the blanking interval ends, the update sequence may be resumed in a continuous manner for the next color field or subfield.

19. The method of claim 18, wherein the update events foor each row are staggered by a stagger interval relative to the update events of a previous row in a row order, the stagger interval has a duration equal to the frame duration divided by the number of said plurality of rows.

20. The method of claim 18, wherein the update events for each row are staggered relative to the update events of a previous row in a row order, wherein during each stagger interval a number of update events occurs, said number of update events occurring during each stagger interval being equal to the number of update events occurring for each row during a frame.

21. The method of claim 18, wherein the FSC system includes a light source and a color wheel, wherein the step of illuminating the pixels with the multiple color fields in a cyclical manner includes the steps of illuminating the color wheel with the light source and rotating the color wheel.

22. The method of claim 18, wherein the color fields include a red (R), a green (G) and a blue (B) color field.

23. A method of driving a spatial light modulator (SLM), wherein the SLM has a plurality of rows, each row having a plurality of pixels, wherein each pixel includes a storage bit and a light-modulating element, and wherein each of the plurality of rows is updated with pixel data at each of a plurality of update events during each of a plurality of frames to be displayed by the SLM, wherein each update event has a predetermined weight, the method comprising the steps of, for each frame:

writing pixel data associated with a first bitplane and a first one of the plurality of rows to the first row at a first update time;

writing pixel data associated with said first bitplane and a second one of the plurality of rows to the second row at a second update time different from the first update time by a stagger interval with duration equal to the frame duration divided by the number of said plurality of rows.

24. The method of claim 23, wherein the first and second rows are physically adjacent to each other.

25. The method of claim 23, wherein the method further comprises the step of, for each of the remaining subsequent rows, writing pixel data associated with said first bitplane and the row to the row at subsequent update times each separated by said stagger interval.

26. The method of claim 25, wherein during each stagger interval, a number of update events occur in the SLM, said number of update events being equal to the number of the plurality of update events occurring to a row during a frame.

27. A method of driving a spatial light modulator (SLM), wherein the SLM has a plurality of rows, each row having a plurality of pixels, wherein each pixel includes a storage bit and a light-modulating element, and wherein each of the plurality of rows is updated with pixel data at a plurality of update events, said events corresponding to at least two bitplanes, during each of a plurality of frames to be displayed by the SLM, wherein each update event has a predetermined weight, the method comprising the steps of, for each frame:

for each row, writing to the row pixel data associated with the row and a first bitplane at a first update event, said first update event occurring at a first update time wherein the first update time for the row is staggered from the first update time of the previous row by a stagger interval with duration equal to the frame duration divided by the number of said plurality of rows; and

for each row, writing to the row pixel data associated with the row and a second bitplane at a second update event, said second update event occurring at a second update time, wherein the second update time for the row is different from the first update time for the row by a duration based on the weight corresponding to the first update event, and wherein the second update time for the row is different from the second update time of the previous row by said stagger interval.

28. The method of claim 27, wherein each row is physically adjacent to its previous row.

29. The method of claim 27, wherein the first update events of each of the plurality of rows are staggered in a logical row order.

30. The method of claim 29, wherein the logical order corresponds to a physically sequential order.

31. The method of claim 29, wherein the logical order corresponds to a physically random order.

32. The method of claim 29, wherein the logical order corresponds to a physically interleaved order.

33. 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 frame is provided without dummy pixel subsets.

34. The method of claim 33, wherein the subsets of the plurality of pixels are rows or columns within a pixel array made up of said plurality of pixels.

49. The method of any of claims 33, 35, 36, 42, or 44, wherein the pixels are deflectable micromirrors or deflectable diffractive elements.

50. The method of any of claims 33, 35, 36, 40, or 44, wherein the pixels comprise liquid crystal and are part of a transmissive or reflective liquid crystal display.

35. 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 length of at least one of the stagger intervals is equal to the frame duration divided by the number of rows.

48. The method of any of claims 35, or 44, wherein the pixel subsets are rows or columns of pixels within a pixel array made up of said plurality of pixels.

36. 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 for at least half of the stagger intervals in a frame, the number of subsets of the plurality of pixels in the spatial light modulator that are updated is the same.

37. The method of claim 36, wherein at least 80% of the stagger intervals in a frame have the same number of pixel subsets updated.

38. The method of claim 37, wherein in all of the stagger intervals, the number of pixel subsets that are updated is the same.

39. The method of claim 36, wherein the pixel subsets are rows or columns of pixels within a pixel array comprising said plurality of pixels.

40. 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 total number of pixel subsets updated in a frame divided by the number of pixel subsets is greater than (X−

20%), where X is the number of bits in an X-bit binary weighted waveform.

41. The method of claim 40, wherein the total number of pixel subsets updated in a frame divided by the number of pixel subsets is greater than (X−

10%).

42. The method of claim 41, wherein the total number of pixel subsets updated in a frame divided by the number of pixel subsets is greater than (X−

1%).

43. The method of claim 40, wherein the pixel subsets are rows or columns of a pixel array made up of said plurality of pixels.

44. A method for displaying a color image, that is made up of a plurality of color component images, comprising:

a) providing a spatial light modulator having a plurality of pixels;

b) displaying a plurality of color component images for each frame on the spatial light modulator, each color component image comprising a plurality of bitplanes;

c) subdividing each frame into a plurality of color fields;

c) subdividing each color field into a plurality of stagger intervals;

d) subdividing each stagger interval into a plurality of subintervals;

e) 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 color component image;

f) wherein the duration of each color field is less than the number of pixel subsets multiplied by the length of the stagger interval.

45. The method of claim 44, wherein the-duration of each color field is one half or less of the number of pixel subsets multiplied by the length of the stagger interval.

46. The method of claim 45, wherein the duration of each color field is from ¼

to ½

the length of the stagger interval multiplied by the number of pixel subsets.

47. The method of claim 44, wherein the pixel subsets are rows or columns in a pixel array made up of said plurality of pixels.

51. 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 means, coupled to the pixel elements, for simultaneously forcing all pixel elements to an off state in response to a blanking signal regardless of the content of the memory cells,

wherein the blanking means 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.

52. 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 means, coupled to the pixel elements, for simultaneously forcing all pixel elements to an off state in response to a blanking signal regardless of the content of the memory cells.

wherein the blanking means 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.