LOW VOLTAGE DRIVER SCHEME FOR INTERFEROMETRIC MODULATORS

• US 20100245313A1
• Filed: 03/27/2009
• Published: 09/30/2010
• Est. Priority Date: 03/27/2009
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chui, Clarence, Cummings, William, Van Lier, Wilhelmus Johannes Robertus, Lewis, Alan G., Mignard, Marc M., Todorovich, Mark M.
• Granted Patent: US 8,405,649 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 3/3466 based on interferometric effect
• CPC Class Codes: H10N 30/802 Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for

Abstract

A method of driving electromechanical devices such as interferometric modulators includes applying a voltage along a common line to release the electromechanical devices along the common line, followed by applying an address voltage along the common line to actuate selected electromechanical devices along the common line based on voltages applied along segment lines. Hold voltages may be applied along common lines between applications of release and address voltages, and the segment voltages may be selected to be sufficiently small that the segment voltages will not affect the state of the electromechanical devices along other common lines not being written to.

Claims

1. A method of driving an array of electromechanical devices, the method comprising:

performing an actuation operation on an electromechanical device within the array, wherein each actuation operation performed on the electromechanical device comprises;

applying a release voltage across the electromechanical device, wherein the release voltage remains between a positive release voltage of said electromechanical device and a negative release voltage of said electromechanical device; and

applying an address voltage across the electromechanical device, wherein the address voltage is either greater than a positive actuation voltage of said electromechanical device or less than a negative actuation voltage of said electromechanical device.

2. The method of claim 1, wherein the release voltage varies between a high voltage which is less than a positive release value of the electromechanical device and a low voltage which is greater than a negative release value of the electromechanical device.

3. The method of claim 1, wherein each actuation operation further comprises applying a hold voltage across the electromechanical device, wherein the hold voltage remains within a hysteresis window of the electromechanical device.

4. The method of claim 3, wherein the hold voltage varies between a high voltage within a hysteresis window of the electromechanical device and a low voltage within the same hysteresis window of the electromechanical device.

5. The method of claim 1, wherein the array of electromechanical devices comprises an array of interferometric modulators.

6. The method of claim 1, additionally comprising performing an actuation operation on a second electromechanical device, wherein the method comprises simultaneously applying a release voltage to said second electromechanical device and applying an address voltage to said first mechanical device.

7. A display comprising a plurality of electromechanical display elements, the display comprising:

an array of electromechanical display elements; and

driver circuitry configured to perform an actuation operation on an electromechanical device within the array, wherein each actuation operation performed on the electromechanical device comprises;

applying a release voltage across the electromechanical device, wherein the release voltage remains between a positive release voltage of said electromechanical device and a negative release voltage of said electromechanical device; and

applying an address voltage across the electromechanical device, wherein the address voltage is either greater than a positive actuation voltage of said electromechanical device or less than a negative actuation voltage of said electromechanical device

8. The display of claim 7, wherein the driver circuitry is further configured to apply a hold voltage across the electromechanical device after applying the address voltage, wherein the hold voltage remains within a hysteresis window of the electromechanical device

9. The display of claim 8, wherein the hold voltage varies between a high voltage within a hysteresis window of the electromechanical device and a low voltage within the same hysteresis window of the electromechanical device.

10. The display of claim 7, wherein the release voltage varies between a high voltage which is less than a positive release value of the electromechanical device and a low voltage which is greater than a negative release value of the electromechanical device.

11. The display of claim 7, wherein the driver circuitry is configured to simultaneously apply a release voltage to a second electromechanical display element and an address voltage to said electromechanical display element.

12. The display of claim 7, wherein the array comprises a plurality of interferometric modulators of a first color and a plurality of interferometric modulators of a second color.

13. The display of claim 12, wherein said electromechanical element comprises an interferometric modulator of the first color, and wherein a second electromechanical element comprises an interferometric modulator of a second color, wherein the driver circuitry is configured to simultaneously apply a release voltage to a second electromechanical display element and an address voltage to said electromechanical display element.

14. A method of driving an electromechanical device in an array of electromechanical devices, the electromechanical device comprising a first electrode in electrical communication with a segment line spaced apart from a second electrode in electrical communication with a common line, the method comprising:

applying a segment voltage on the segment line, wherein the segment voltage varies between a maximum voltage and a minimum voltage, and wherein a difference between the maximum voltage and the minimum voltage is less than a width of a hysteresis window of the electromechanical device;

applying a reset voltage on the common line, wherein the reset voltage is configured to place the electromechanical device in an unactuated state; and

applying an overdrive voltage on the common line, wherein the overdrive voltage is configured to cause the electromechanical device to actuate based upon the state of the segment voltage.

15. The display of claim 14, additionally comprising applying a hold voltage on the common line, wherein the hold voltage is configured to maintain the electromechanical device in its current state, regardless of the state of the segment voltage.

16. The method of claim 15, wherein the hold voltage is applied after applying the reset voltage and prior to applying the overdrive voltage.

17. The method of claim 15, wherein the hold voltage is applied after applying the overdrive voltage.

18. The method of claim 17, additionally comprising a second hold voltage after applying the reset voltage and prior to applying the overdrive voltage, wherein the first hold voltage is within a first hysteresis window of the electromechanical device and wherein the second hold voltage is within a second hysteresis window of the electromechanical device.

19. The method of claim 18, wherein applying a reset voltage comprises applying a voltage on the common which varies from the first hold voltage to the second hold voltage, the voltage remaining within a release window of the electromechanical device for a period of time sufficient to cause release of the electromechanical device.

20. The method of claim 15, wherein an absolute value of the overdrive voltage is greater than an absolute value of the hold voltage.

21. The method of claim 15, wherein the hold voltage lies within a hysteresis window of the electromechanical device.

22. A method of driving an array of electromechanical devices, the array including a plurality of common lines and a plurality of segment lines, each electromechanical device comprising a first electrode in electrical communication with a common line spaced apart from a second electrode in electrical communication with a segment line, the method comprising:

applying a segment voltage on each of the plurality of segment lines, wherein the segment voltage applied on a given segment line is switchable between a high segment voltage state and low segment voltage state; and

simultaneously applying a release voltage on a first common line and an address voltage on a second common line, wherein the release voltage causes release of all actuated electromechanical devices along the first common line independent of the state of a segment voltage applied to each electromechanical device, and wherein the address voltage causes actuation of electromechanical devices dependent upon the state of the segment voltage applied to a given electromechanical device.

23. The method of claim 22, wherein the address voltage is applied on the second common line after release of any actuated electromechanical devices located along said second common line.

24. The method of claim 22, additionally comprising applying a hold voltage on the second common line after applying the address voltage, wherein the hold voltage maintains the electromechanical devices along the second common line in their current state, independent the state of the segment voltage applied to each of the electromechanical devices.

25. The method of claim 22, wherein the array includes a first plurality of electromechanical devices configured to reflect a first color in an actuated position, and a second plurality of electromechanical devices configured to reflect a second color in an actuated position.

26. The method of claim 25, wherein said first plurality of electromechanical devices are arranged along a first common line, and wherein said second plurality of electromechanical devices are arranged along a second common line.

27. The method of claim 26, wherein the address voltage applied on the first common line is a first address voltage, wherein the address voltage applied on the second common line is a second address voltage, and wherein the first address voltage is different from the second address voltage.

28. The method of claim 25, wherein said first plurality of electromechanical devices are arranged along a first segment line, and wherein said second plurality of electromechanical devices are arranged along a second segment line.

29. The method of claim 28, wherein the segment voltage applied on the first segment line varies between a first high segment voltage and a first low segment voltage, wherein the segment voltage applied on the second segment line varies between a second high segment voltage and a second low segment voltage, and wherein the first high segment voltage is different from the second high segment voltage.

30. A display device, comprising:

an array of electromechanical devices, the array comprising a plurality of common lines and a plurality of segment lines, each electromechanical device comprising a first electrode in electrical communication with a common line spaced apart from a second electrode in electrical communication with a segment line; and

driver circuitry configured to apply high segment voltage and a low segment voltage on segment lines, and configured to apply release voltages and address voltages on common lines, wherein the driver circuitry is configured to simultaneously apply a release voltage along a first common line and an address voltage along a second common line;

wherein the high and low segment voltages are selected such that the release voltages release electromechanical devices located along a common line regardless of the applied segment voltage, and the address voltages cause actuation of certain electromechanical devices along a common line dependent upon the applied segment voltage.

31. The display device of claim 30, wherein the driver circuitry is further configured to apply hold voltages on common lines, wherein the hold voltages maintain the electromechanical devices along a common line in their current state regardless of the applied segment voltage

32. The display device of claim 31, wherein the driver circuitry is configured to apply one of a release voltage, a high hold voltage, a high address voltage, a low hold voltage, and a low address voltage.

33. The display device of claim 32, wherein a given electromechanical device actuates subsequent to application of the high address voltage on a corresponding common line, and application of the low segment voltage on a corresponding segment line.

34. The display device of claim 32, wherein a given electromechanical device actuates subsequent to application of the low address voltage on a corresponding common line, and application of the high segment voltage on a corresponding segment line.

35. The display device of claim 31, wherein the driver circuitry is further configured to apply the same segment voltages on each of the segment lines when no address voltages are being applied on any common lines.

36. The display device of claim 31, wherein the driver circuitry is further configured to apply optimized hold voltages when no address voltages are being applied on any common lines, wherein the optimized hold voltages are configured to maintain unactuated electromechanical devices in a desired unactuated position.

37. The display device of claim 36, wherein the optimized hold voltages are selected at least in part based on the resultant the white balance of the array when the optimized hold voltages are applied.

38. The display device of claim 36, wherein the optimized hold voltages are different from the hold voltages.

39. A method of balancing charges within an array of electromechanical devices, the array comprising a plurality of segment lines and a plurality of common lines, the method comprising:

performing a write operation on said common line, wherein performing a write operation comprises;

selecting a polarity for said write operation based at least in part on charge-balancing criteria;

performing a reset operation by applying a reset voltage across a common line, the reset voltage placing each of the electromechanical devices along a common line in an unactuated state;

applying a hold voltage of said selected polarity across said common line, wherein the hold voltage does not cause any of the electromechanical devices along said common line to actuate; and

simultaneously applying an overdrive voltage of said selected polarity across said common line and a plurality of segment voltages across said segment lines, wherein the segment voltages vary between a first polarity and a second polarity, and wherein said overdrive voltage causes the actuation of an electromechanical device when the polarity of the overdrive voltage and the polarity of the corresponding segment voltage are not the same.

40. The method of claim 39, wherein selecting a polarity for said write operation comprises alternating the polarity of write operations on said common line.

41. The method of claim 39, wherein selecting a polarity for said write operation comprises selecting a polarity in a pseudo-random manner.

42. The method of claim 42, wherein selecting a polarity for said write operation in a pseudo-random manner comprises selecting a polarity for a first common line in a pseudo-random pattern, the method further comprising determining a polarity for subsequent write operations in a frame based upon the selected polarity for the first common line.