Methods and apparatus for selectively updating memory cell arrays

• US 7,027,205 B2
• Filed: 11/12/2004
• Issued: 04/11/2006
• Est. Priority Date: 04/02/2003
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Richards, Peter W.
• Primary Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US10/987,896
• Publication Number:
  US 20050088383A1
• Time in Patent Office: 515 Days
• Field of Search: 359/291, 359/290, 359/292, 359/295, 359/297, 359/238, 359/242, 359/223, 359/224
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066
• CPC Class Codes: G09G 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• CPC Class Codes: G09G 2310/02 Addressing, scanning or driving the display screen or processing steps related thereto
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0266 Reduction of sub-frame artefacts
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/34 by control of light from an independent source
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: G11C 11/408 Address circuits
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

Methods and apparatus for selectively updating memory cells of a memory cell array are provided. The memory cells of each row of the memory cell array are provided with a plurality of wordlines. Memory cells of the row are activated and updated by separated wordlines. In an application of display systems using memory cell arrays for controlling the pixels of the display system and pulse-width-modulation (PWM) technique for displaying grayscales, the pixels can be modulated by different PWM waveforms. The perceived dynamic-false-contouring artifacts are reduced thereby. In another application, the provision of multiple wordlines enables precise measurements of voltages maintained by memory cells of the memory cell array.

Claims

1. A method comprising:

providing a memory-cell array comprising a plurality of memory cells;

connecting each memory cell of an array of memory cells to one of an array of electrodes such that an electrostatic property of the electrode can be altered in accordance with information stored in the memory cell;

providing a micromirror array comprising an array of reflective and deflectable mirror plates that are coupled with the array of electrodes such that the mirror plates can be individually moved by the electrodes; and

activating the memory cells of a row of the array using a plurality of separate word lines of the row such that;

at least two memory cells of the row are activated by separate word lines;

wherein

each wordline of the plurality of wordlines connects memory cells of the same row of the array.

2. The method of claim 1, wherein the number of the plurality of separate word lines of the row is 2.

3. The method of claim 1, wherein the step of activating the memory cells of a row of the array using a plurality of separate word lines further comprises:

dividing the memory cells in a row of the array into a set of subgroups according to a predefined criterion; and

coupling the memory cells with the separate word lines of the row such that the memory cells in the same subgroup are coupled with the same word line, and the memory cells in different subgroups are coupled with separate word lines.

4. The method of claim 2, wherein the criterion comprises:

that adjacent memory cells in a row are grouped into different subgroups.

5. The method of claim 2, wherein the criterion comprises:

that the memory cells in a subgroup of a row are randomly selected from the memory cells of the row.

6. The method of claim 2, wherein the criterion comprises:

that in a row, the positions of the memory cells in at least two subgroups are interleaved.

7. The method of claim 1, wherein the micromirror is a type of deflectable reflective micromirror having a size in the order of microns.

8. The method of claim 1, wherein the micromirror array is formed on a first substrate and the electrode array is formed on a second substrate other than the first substrate.

9. The method of claim 1, wherein the micromirror array is formed on the electrode array.

10. The method of claim 1, further comprising:

writing a set of information into the activated memory cells using one or more bit lines.

11. The method of claim 9, wherein the step of writings set of information into the activated memory cells further comprises:

defining at least a first set of waveforms in accordance with a first waveform-format based on a pulse-width-modulation technique;

defining at least a second sot of waveforms in accordance with a second waveform-format based on a pulse-width-modulation technique; and

writing the actuated memory cells in response to the first and second sets of waveforms such that at least two memory cells of the row are written in response to at least two waveforms selected from the first and second sets of waveforms.

12. The method of claim 10, wherein the defined waveform is a binary-weighted waveform.

13. The method of claim 10, wherein the defined waveform is a non-binary-weighted waveform.

14. The method of claim 2, wherein the number of the set of subgroups is 2.

15. The method of claim 2, further comprising:

activating the memory cells in the row using the separate word lines such that memory cells in different subgroups are activated using separate word lines.

16. The method of claim 1, further comprising:

directing an incident light onto the micromirrors;

selectively altering the electrostatic property of each electrode in accordance with the information stored in the memory cell connected to the electrode;

selectively deflecting each micromirror electrostatically according to the altered electrostatic property of the electrode coupled with the micromirror; and

reflecting the incident light, by the deflected micromirror into an optical device.

42. The method of claim 1, wherein each wordline of the plurality of wordlines is along a row of the array.

17. A method for operating a memory cell array of a spatial light modulator of a display system, the memory cell array comprising a plurality of memory cells, the method comprising:

grouping the memory cells in each row of the memory cell array into a set of subgroups according to a predefined criterion, each subgroup comprising at least one memory cell;

connecting the memory cells to a plurality of wordlines such that memory cells in the same subgroup are connected to the same wordline, and memory cells in different subgroups are connected to separate wordlines;

activating the memory cells in a first subgroup connected to a first wordline of a first row of the memory cell array; and

activating the memory cells in a second subgroup connected to a second wordline of a second row of the memory cell array.

18. The method of claim 17, wherein the activation of the memory cells in the first subgroup and the activation of the memory cells in the second subgroup are performed simultaneously.

19. The method of claim 17, wherein the first subgroup comprises the even numbered memory cells of the first row;

and wherein the second subgroup comprises the odd numbered memory cells of the second row.

20. The method of claim 19, wherein the memory cells of the first subgroup are connected to a firs subset of a plurality of bitlines of the memory cell array, and the memory cells of the second subgroup are connected to a second subset other than the first subset of the plurality of bitlines.

21. A system comprising:

a memory-cell array comprising a plurality of memory cells;

an electrode array having a plurality of electrodes, wherein each electrode is connected to one memory cell of the plurality of memory cells such that an electrostatic property of the electrode can be altered corresponding to information stored within the memory cell, wherein the information stored in the memory cell is the voltage stored by the memory cell; and

a plurality of word-lines coupled to the memory cells of a row of the memory-cell array for selectively activating the memory cells such that at least two memory cells of the row are coupled to separate word-lines of the plurality of word-lines.

22. The system of claim 21, wherein the memory cell is a standard DRAM.

23. The system of claim 21, wherein the memory cell is a charge-pump pixel cell.

24. The system of claim 21, wherein the memory cells in a row of the memory cell array are divided into a plurality of subgroups according to a predefined criterion.

25. The system of claim 24, wherein the predefined criterion comprises:

that the adjacent memory cells in a row are divided into different groups of the plurality of subgroups.

26. The system of claim 24, wherein the predefined criterion comprises:

that the memory cells in a subgroup of the plurality of subgroups are randomly selected from the memory cells of the row.

27. The system of claim 24, wherein the predefined criterion comprises:

that in a row, the positions of the memory cells in at least two subgroups are interleaved.

28. The system of claim 24, wherein the memory cells in different subgroups are coupled with separate word lines of the plurality of word lines, and the memory cells in the same subgroup are coupled wit only one word line of the plurality of word lines.

29. The system of claim 21, further comprising:

an micromirror array having a plurality of micromirrors, each micromirror is a deflectable reflective micromirror having a size in the order of microns, wherein each micromirror is coupled with one electrode of the electrode array such that the micromirror can be electrostatically controlled by the electrode coupled with the micromirror.

30. The system of claim 29, further comprising:

a first substrate for forming the micromirror array thereon; and

a second substrate for forming the memory cell array thereon.

31. The system of claim 30, wherein the first substrate is transparent to visible light.

32. The system of claim 30, wherein the second substrate is a silicon wafer.

33. The system of claim 30, wherein the micromirror array is formed on the memory cells array.

34. The system of claim 32, wherein the first and the second substrates are bonded together.

35. The system of claim 32, further comprising:

a first set of waveforms for updating the micromirrors such that the micromirrors generate a gray-scale image, wherein each waveform of the first set of waveforms is created in accordance with the gray scales of the image and a first waveform format that is defined based on a pulse-width-modulation technique; and

a second set of waveforms for updating the micromirrors such that the micromirrors are able to create an image pattern that is different from the gray-scale image, wherein each waveform of the second set of waveforms is generated in accordance with a second waveform format that is defined based on the pulse-width-modulation technique, and the second waveform format is different from the first waveform format.

36. The system of claim 21, further comprising:

a plurality of bit lines for writing the memory cells based on the waveforms selected from the first and second sets of waveforms.

37. The method of claim 35, wherein each waveform of the first set of waveforms is a binary-weighted waveform starting from a least significant bit and ending at a most significant bit.

38. The method of claim 35, wherein each waveform of the first set of waveforms is a non-binary-weighted waveform.

39. The method of claim 35, wherein each waveform of the second set of waveforms is a binary-weighted waveform staffing from a most significant bit and ending at a least significant bit.

40. The method of claim 35, wherein each waveform of the first set of waveforms is a non-binary-weighted waveform.

41. The method of claim 35, wherein each waveform of the first and second sets of waveforms comprises a sequence of updating intervals, and the duration of the intervals are different in the waveforms of the first and second sets of waveforms.