Micromirror modulation method and digital apparatus with improved grayscale

• US 6,999,224 B2
• Filed: 03/10/2004
• Issued: 02/14/2006
• Est. Priority Date: 03/10/2004
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Huibers, Andrew
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US10/798,777
• Publication Number:
  US 20050200939A1
• Time in Patent Office: 706 Days
• Field of Search: 359/290
• US Class Current: 359/290
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H04N 9/312 Driving therefor driving of electronic spatial light modulators in displays other than projection devices G09G3/34, G09G3/36; control of liquid crystal elements G02F1/133; control of micromechanical modulators G02B26/08
• CPC Class Codes: H04N 9/3182 Colour adjustment, e.g. white balance, shading or gamut white balance per se H04N9/73; control of amplitude of colour signals H04N9/68; colour control circuits for displays in general G09G5/02, G09G3/2003, G09G3/3607

Abstract

A method and apparatus are disclosed for increasing contrast in micromirror-based image display devices. As a result the displayed image is a more faithful reproduction of the original and is more pleasing to human perception than is possible with a low contrast display. The method and apparatus comprise a micromirror design and a modulation scheme for driving micromirrors with a combination of analog and digital techniques to achieve partial and full micromirror deflection. The analog techniques permit the mirrors to be deflected to positions intermediate between the resting position and the position of maximum deflection. These intermediate deflections appear as intermediate light levels in an image. Compared to digital modulation, the analog techniques provide an increase in the number of light levels that can be displayed by a system that is limited by its incoming data rate and maximum micromirror speed.

Claims

1. A method for displaying an image, comprising:

directing light onto a micromirror array;

modulating micromirrors within the micromirror array; and

using analog modulation in combination with digital modulation to achieve grayscale levels in the displayed image.

2. The method as in claim 1 wherein the number of grayscale levels in the displayed image is greater than the number of time slots per image frame time.

3. An apparatus for displaying an image, comprising:

micromirrors in a micromirror array; and

an electronic controller which sends analog or digital control signals, depending on the light level desired, to the micromirrors in the micromirror array.

4. The apparatus as in claim 3 wherein, the electronic controller uses an algorithm or a lookup table to convert linear encoded light level data to nonlinear analog or digital micromirror control signals.

5. The apparatus as in claim 3 wherein, the analog control signals are amplitude modulated signals and the digital control signals are digital pulsewidth modulated signals.

6. The apparatus as in any of claims 3, wherein each micromirror in the micromirror array has only one landing pad or mechanical stop.

7. The apparatus as in claim 6, wherein, the micromirrors in the micromirror array are deflected by the application of electrostatic force.

8. The apparatus as in claim 7 wherein, the micromirrors in the micromirror array are deflected to positions intermediate between the resting position and the maximum deflection position.

9. The apparatus as in claim 8 wherein, the micromirrors in the micromirror array always return to the same position when electrostatic forces are removed.

10. The apparatus as in claim 8 wherein, only one electrical pulse is used per image frame.

11. The apparatus as in claim 8 wherein, more than one electrical pulse is used to direct the micromirror to a position intermediate between the resting position and the maximum deflection position.

12. The apparatus as in claim 8 wherein, the amount of light appearing at a pixel in the image during an image frame depends on the duration of the application of electrical force to the micromirror corresponding to the pixel such that

when the duration of the force is less than that required to move the micromirror to its position of maximum deflection, the amount of light appearing at the pixel in the image during the image frame is approximately proportional to the square of the duration of the force;

and

when the duration of the force is more than that required to move the micromirror to its position of maximum deflection, the amount of light appearing at the pixel in the image during the image frame is approximately linearly proportional to the duration of the force.

13. The apparatus as in claim 9 wherein, when an electrical control pulse is applied to a micromirror in the micromirror array, the release of stored mechanical energy is not significant compared to the electrostatic force applied.

14. The apparatus as in claim 13 wherein, no stored mechanical energy is released when the micromirror is deflected by electrostatic force.

15. A method for displaying an image, comprising:

directing light onto an array of tilting micromirrors;

tilting micromirrors within the micromirror array; and

using analog and digital techniques wherein the

analog techniques include tilting the micromirrors to arbitrary angles between their minimum and maximum deflection angles, and the

digital techniques include tilting the micromirrors to only their minimum or maximum deflection angles for varying time periods.

16. A method for displaying an image, comprising:

directing light onto an array of tilting, flat-plate micromirrors;

deflecting micromirrors within the micromirror array to various tilt angles;

combining analog and digital techniques to control the tilt angles according to digitally encoded pixel intensity data.

17. The method as in claim 16 wherein,

maximum and minimum tilt angles are controlled using digital techniques for all but the least significant bit of the intensity data, and

intermediate tilt angles are controlled by analog techniques for the least significant bit of the intensity data.

18. An apparatus for displaying an image, comprising:

micromirrors in a micromirror array; and

an electronic controller which sends analog modulated control signals in combination with digital modulated control signals appropriate to partially deflect or fully deflect, depending on the light level desired, the micromirrors in the micromirror array.

19. The apparatus as in claim 18 wherein, the electronic controller uses an algorithm or a lookup table to convert linear encoded light level data to micromirror control data that results in partial or full micromirror deflection signals.

20. The apparatus as in claim 18 wherein, the analog control signals are amplitude modulated signals and the digital control signals are digital pulsewidth modulated signals.

21. The apparatus as in any of claim 18 wherein, each micromirror in the micromirror array has only one landing pad or mechanical stop.

22. The apparatus as in claim 21 wherein, the micromirrors in the micromirror array are deflected by the application of electrostatic force.

23. The apparatus as in claim 22 wherein, the micromirrors in the micromirror array are deflected to positions intermediate between the resting position and the maximum deflection position.

24. The apparatus as in claim 23 wherein, the micromirrors in the micromirror array always return to the same position when electrostatic forces are removed.

25. The apparatus as in claim 23 wherein, only one electrical pulse is used per image frame.

26. The apparatus as in claim 23 wherein, more than one electrical pulse is used to direct the micromirror to a position intermediate between the resting position and the maximum deflection position.

27. The apparatus as in claim 23 wherein, the amount of light appearing at a pixel in the image during an image frame depends on the duration of the application of electrical force to the micromirror corresponding to the pixel such that

when the duration of the force is less than that required to move the micromirror to its position of maximum deflection, the amount of light appearing at the pixel in the image during the image frame is not linearly proportional to the duration of the force;

and

when the duration of the force is more than that required to move the micromirror to its position of maximum deflection, the amount of light appearing at the pixel in the image during the image frame is approximately linearly proportional to the duration of the force.

28. The apparatus as in claim 24 wherein, when an electrical control pulse is applied to a micromirror in the micromirror array, the release of stored mechanical energy is not significant compared to the electrostatic force applied.

29. The apparatus as in claim 28 wherein, no stored mechanical energy is released when the micromirror is deflected by electrostatic force.

30. A method for displaying an image, comprising:

directing light onto a micromirror array;

modulating micromirrors within the micromirror array; and

,

using analog modulation in combination with digital modulation to achieve grayscale levels in the displayed image, wherein

analog modulation includes operation of a micromirror where the micromirror is deflected to an angle θ

₁ less than its maximum possible deflection angle θ

_max and remains deflected to angle θ

₁ with approximately zero angular velocity for longer than an instantaneous time, i.e. the time for which the angular velocity is zero during a velocity reversal encountered at the extreme points in the motion of a vibrating micromirror in the absence of electrostatic driving forces.

31. The method as in claim 30 wherein the digital modulation is pulsewidth modulation.

32. The method as in claim 30 wherein the micromirror is deflected to, or stopped at, angle θ

₁ through the application of analog control voltages to one or more control electrodes.

33. The method as in claim 30 wherein the micromirror is deflected to, or stopped at, angle θ

₁ by mechanical stops.

34. The method as in claim 30 wherein the micromirror is deflected to, or stopped at, angle θ

₁ by remaining at a natural rest position intermediate between positions achieved by electrostatic actuation.

35. The method as in claim 30 wherein the micromirror is deflected to one of a plurality of possible deflection angles θ

_i less than its maximum possible deflection angle θ

_max.

36. A method for displaying an image, comprising:

directing light onto a micromirror array;

deflecting micromirrors within the micromirror array; and

using a plurality of micromirror deflection angles to achieve grayscale levels in the displayed image wherein the brightness of one or more pixels in the image is controlled by analog modulation of a micromirror or micromirrors and the brightness of one or more other pixels in the image is controlled by digital pulsewidth modulation of a micromirror or micromirrors.