Method for operating a micromirror device with electromechanical pulse width modulation

• US 8,797,629 B2
• Filed: 10/04/2011
• Issued: 08/05/2014
• Est. Priority Date: 04/24/2009
• Status: Active Grant

• Current Assignee: IMEC International, Universiteit Gent Vzw
• Original Assignee: IMEC International, Universiteit Gent Vzw
• Inventors: De Smet, Herbert, Beernaert, Roel
• Primary Examiner(s): Ben, Loha
• Application Number:
  US13/252,927
• Publication Number:
  US 20120062978A1
• Time in Patent Office: 1,036 Days
• Field of Search: 359290-295, 359/298, 359/213.1, 359/220.1, 359/225.1, 359/224.1, 359/847, 359/872, 355/67, 355/77, 310/309, 216/24, 216/37, 735/040.2, 735/143.2
• US Class Current: 359/290
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833

Abstract

A method of operating by pulse width modulation a micromirror device is disclosed. In one aspect, the method includes providing a micromirror device having a micromirror element electrostatically deflectable around a rotation axis between a first and second position. The micromirror element is controllable by applying voltage signals to a first and second electrode on one side of the rotation axis and a third and fourth electrode on the other side. The method includes associating an intermediate value of intensity to the micromirror element during a time frame, the intensity being between a first value corresponding to the first position and a second value corresponding to the second position. The method includes switching the micromirror element between the first and second position. The intermediate value corresponds to the ratio of periods in the time frame in which the micromirror element is in the first or second position.

Claims

1. A method of operating a micromirror device comprising:

providing a micromirror device comprising at least one micromirror element being electrostatically deflectable around a rotation axis between at least two positions being a first position and a second position, the micromirror element being controlled by applying voltage signals to at least four electrodes, the four electrodes comprising a first and second electrode located on one side of the rotation axis and a third and fourth electrode on the other side;

associating an intermediate value of intensity to the micromirror element during a time frame, the intensity being between a first value and a second value, the first value corresponding to the first position and the second value corresponding to the second position;

switching the micromirror element between the first position and the second position and vice-versa so that the micromirror element is either in the first position or in the second position, the intermediate value of intensity corresponding to a ratio of periods of time in the time frame in which the micromirror element is either in the first position or in the second position,

wherein the switching is obtained by applying fixed voltage signals to the second and third electrodes during the time frame while applying periodic voltage signals having a period equal to the length of the time frame to the first and fourth electrodes, the fixed voltage signals being kept constant during half of the time frame.

2. The method according to claim 1, wherein the periodic signals are characterized by a monotonic variation in a first half of their period, and a monotonic variation in a second half of their period.

3. The method according to claim 1, wherein the first and fourth voltage signals are antiphase signals.

4. The method according to claim 1, wherein the periodic voltage signals correspond to voltage differences that are directly applied between the micromirror element and the first and fourth electrodes, and wherein the second and third fixed voltage signals correspond to voltage differences that are applied between the micromirror element and the second and third electrodes.

5. The method according to claim 1, wherein the periodic voltage signals are in the form of a triangular waveform, a saw-tooth waveform, gamma corrected triangular waveform, or sinusoidal waveform signal.

6. The method according to claim 1, wherein the first value of intensity corresponds to a white pixel while the second value of intensity corresponds to a black pixel with the intermediate value of intensity corresponding to gray levels in between.

7. The method according to claim 1, wherein the first value of intensity corresponds to a colored status while the second value of intensity corresponds to a non colored status with intermediate colored levels in between.

8. A micromirror device comprising:

at least one micromirror, each micromirror being configured to rotate along an axis parallel to the micromirror from a first position to a second position;

a substrate underneath the micromirror;

at least four controlling electrodes for each micromirror, the at least four controlling electrodes comprising a first and a second set, each set comprising two controlling electrodes, a first controlling electrode of each set being located on one side of the rotation axis of the micromirror and a second controlling electrode of each set being located on the other side of the rotation axis of the micromirror,

wherein each electrode of the second set is connected to a circuit, the circuit being configured to keep, in use, a constant analog voltage signal during half of a time frame.

9. The micromirror device according to claim 8, wherein the circuit connected to each electrode of the second set comprises a storage capacitor configured to keep a fixed analog voltage during the time frame.

10. The micromirror device according to claim 9, wherein the circuit connected to each electrode of the second set comprises a MOSFET switch.

11. A spatial light modulator comprising a micromirror device according to claim 8.

12. A system for operating a micromirror device, the micromirror device comprising at least one micromirror element being electrostatically deflectable around a rotation axis between at least two positions being a first position and a second position, the micromirror device further comprising a first and second electrode located on one side of the rotation axis and a third and fourth electrode on the other side, the system comprising:

means for associating an intermediate value of intensity to the micromirror element during a time frame, the intensity being between a first value and a second value, the first value corresponding to the first position and the second value corresponding to the second position; and

means for switching the micromirror element between the first position and the second position and vice-versa so that the micromirror element is either in the first position or in the second position, the intermediate value of intensity corresponding to a ratio of periods of time in the time frame in which the micromirror element is either in the first position or in the second position,

wherein the switching is obtained by applying fixed voltage signals to the second and third electrodes during the time frame while applying periodic voltage signals having a period equal to the length of the time frame to the first and fourth electrodes, the fixed voltage signals being kept constant during half of the time frame.

13. The system according to claim 12, wherein the periodic signals are characterized by a monotonic variation in a first half of their period, and a monotonic variation in a second half of their period.

14. The system according to claim 12, wherein the first and fourth voltage signals are antiphase signals.

15. The system according to claim 12, wherein the periodic voltage signals correspond to voltage differences that are directly applied between the micromirror element and the first and fourth electrodes, and wherein the second and third fixed voltage signals correspond to voltage differences that are applied between the micromirror element and the second and third electrodes.

16. The system according to claim 12, wherein the periodic voltage signals are in the form of a triangular waveform, a saw-tooth waveform, gamma corrected triangular waveform, or sinusoidal waveform signal.

17. The system according to claim 12, wherein the first value of intensity corresponds to a white pixel while the second value of intensity corresponds to a black pixel with the intermediate value of intensity corresponding to gray levels in between.

18. The system according to claim 12, wherein the first value of intensity corresponds to a colored status while the second value of intensity corresponds to a non colored status with intermediate colored levels in between.