Voltage biased pull analog interferometric modulator with charge injection control

• US 9,035,934 B2
• Filed: 05/02/2012
• Issued: 05/19/2015
• Est. Priority Date: 05/02/2012
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chan, Edward K., Hong, John H., Kim, Cheonhong, Lee, Chong U., Wen, Bing
• Primary Examiner(s): REGN, MARK W
• Application Number:
  US13/462,696
• Publication Number:
  US 20130293523A1
• Time in Patent Office: 1,112 Days
• Field of Search: 345/204, 345/211, 345/212
• US Class Current: 345/212
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2310/0272 Details of drivers for data electrodes, the drivers communicating data to the pixels by means of a current
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 3/3466 based on interferometric effect
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

This disclosure provides systems, methods and apparatus for driving three-terminal electromechanical systems (EMS) devices. The driving systems and methods described herein include a switched capacitor charge injection circuit that is configured to isolate a single EMS device and transfer a desired amount of charge to the isolated device such that the device can be actuated to produce a desired optical, electrical or mechanical effect. The charge injection circuit can include an operational amplifier and can be connected such that the EMS device is placed in the feedback path of the operational amplifier.

Claims

1. An apparatus, comprising:

an array of three terminal electromechanical systems (EMS) devices arranged in a plurality of rows and columns, each EMS device including;

a first stationary electrode layer connected to a first drive line;

a movable electrode layer connected to a second drive line; and

a second stationary electrode layer connected to a third drive line, the movable electrode layer disposed between the first and the second stationary electrode layers,

wherein a portion of the movable electrode layer and the first stationary electrode layer form a first variable capacitor having a first variable capacitance value, and

wherein a portion of the movable electrode layer and the second stationary electrode layer form a second variable capacitor having a second variable capacitance value;

a bias voltage circuit having a bias voltage line connected to the third drive line of each of the EMS devices in a column of the array, the bias voltage circuit configured to provide a potential difference between the second stationary electrode layer and the movable electrode layer; and

a charge injection circuit configured to electrically connect to the first drive line and the second drive line of each of the EMS devices in the column of the array such that the charge injection circuit is electrically connected to the first and second drive line of only one of the EMS devices at any one time to provide a desired charge to the first stationary electrode layer,

wherein the charge injection circuit includes;

an operational amplifier having an inverting input line, a non-inverting input line, and an output line, the inverting input line of the operational amplifier being electrically connected to the second drive line of each of the EMS devices in the column;

a plurality of row-select switches controlled to selectively electrically connect the output line of the operational amplifier to the first drive line of each of the EMS devices in the column such that the output line of the operational amplifier is electrically connected to the first drive line of only one EMS device at any one time; and

an input capacitor circuit configured to be electrically connected to the inverting line of the operational amplifier or to a voltage circuit for charging the input capacitor circuit to a charge Q_in,

wherein the charge injection circuit is controlled to selectively connect the first drive line of each EMS device in the column, for each of the display elements in the column, to the output line of the operational amplifier while a charge from the input capacitor circuit is transferred to the first drive line of the EMS device electrically connected to the charge injection circuit.

2. The apparatus of claim 1, further comprising an operational amplifier grounding switch coupled between the operational amplifier output line and the operational amplifier inverting line.

3. The apparatus of claim 1, wherein the movable electrode layer of each EMS device includes a first conductor proximal to the first stationary electrode layer and a second conductor proximal to the second stationary electrode layer, the first conductor connected to the second drive line and electrically insulated from the second conductor, the first conductor and the first stationary electrode layer forming the first variable capacitor, the second conductor and the second stationary electrode layer forming the second variable capacitor.

4. The apparatus of claim 3, further comprising a movable electrode reset switch configured to connect the second conductor of the movable electrode layer of each EMS devices to an electrical ground.

5. The apparatus of claim 3, further comprising a storage capacitor having a storage capacitance value, the storage capacitor electrically connected between the first stationary electrode layer and the first conductor of the movable electrode layer of each of the EMS devices.

6. The apparatus of claim 5, wherein the storage capacitance has a value that is greater than a smallest value of the first variable capacitance.

7. The apparatus of claim 1, further comprising a bypass capacitor having a bypass capacitance value electrically connected between the inverting line of the operational amplifier and the bias voltage line of the bias voltage circuit.

8. The apparatus of claim 7, wherein the bypass capacitance value is greater than a sum of the second variable capacitance values for all the electromechanical systems devices in the column.

9. The apparatus of claim 7, wherein the bypass capacitor is connected to a charging voltage source through a charging switch.

10. The apparatus of claim 1, further comprising a clamping diode electrically connected between the inverting line and the non-inverting line of the operational amplifier.

11. The apparatus of claim 1, wherein the charge injection circuit is configured to transfer about 10 picocoulombs of charge in about 10 microseconds.

12. The apparatus of claim 1, wherein each of the EMS devices is a display pixel or a portion of a display pixel.

13. The apparatus of claim 12, wherein each of the EMS devices includes an IMOD.

14. The apparatus of claim 12, further comprising:

a display;

a processor that is configured to communicate with the display, the processor being configured to process image data; and

a memory device that is configured to communicate with the processor.

15. The apparatus as recited in claim 14, further comprising:

a driver circuit configured to send at least one signal to the display;

a controller configured to send at least a portion of the image data to the driver circuit; and

an image source module configured to send the image data to the processor, wherein the image source module includes at least one of a receiver, transceiver, and transmitter.

16. The apparatus as recited in claim 14, further comprising:

an input device configured to receive input data and to communicate the input data to the processor.

17. A method of calibrating a three-terminal electromechanical systems (EMS) device in the apparatus of claim 14, the method comprising:

providing a first amount of known charge to the EMS device;

determining a first calculated voltage value for voltage developed across the first stationary electrode and the movable electrode in response to the provided first amount of known charge;

measuring a first voltage value across the first stationary electrode and the movable electrode in response to the provided first amount of known charge;

comparing the first calculated voltage value with the measured first voltage value to obtain a first difference value;

providing a second amount of known charge to the EMS device;

determining a second calculated voltage value for voltage developed across the first stationary electrode and the movable electrode in response to the provided second amount of known charge;

measuring a second voltage value across the first stationary electrode and the movable electrode in response to the provided second amount of known charge;

comparing the second calculated voltage value with the measured second voltage value to obtain a second difference value;

determining calibration information of at least one of a stiffness constant of the movable electrode and a launch bias of the movable electrode based on the first and second difference values; and

storing the calibration information in the memory of the apparatus.

18. An apparatus, comprising:

an array of three terminal electromechanical systems (EMS) devices arranged in a plurality of rows and columns, each EMS device including;

a first stationary means for conducting electricity connected to a first drive line;

a movable means for conducting electricity connected to a second drive line; and

a second stationary means for conducting electricity connected to a third drive line, the movable conducting means disposed between the first and the second stationary conducting means,

wherein a portion of the movable conducting means and the first stationary conducting means form a first variable capacitor having a first variable capacitance value, and

wherein a portion of the movable conducting means and the second stationary conducting means form a second variable capacitor having a second variable capacitance value;

a bias voltage circuit having a bias voltage line connected to the third drive line of each of the EMS devices in a column of the array, the bias voltage circuit configured to provide a potential difference between the second stationary conducting means and the movable conducting means; and

a means for injecting electrical charge configured to electrically connect to the first drive line and the second drive line of each of the EMS devices in the column of the array such that the charge injecting means is electrically connected to the first and second drive line of only one of the EMS devices at any one time to provide a desired charge to the first stationary conducting means, wherein the charge injecting means includes

a means for amplifying having a means for inverting an input, a means for non-inverting an input, and a means for providing an output, the input inverting means being electrically connected to the second drive line of each of the EMS devices in the column;

a plurality of means for selectively electrically connecting the output providing means to the first drive line of each of the EMS devices in the column such that the output providing means is electrically connected to the first drive line of only one EMS device at any one time; and

means for storing capacitance configured to be electrically connected to the input inverting means or to a means for charging the capacitance storing means to a charge Q_in,

wherein the charge injecting means is controlled to selectively connect the first drive line of each EMS device in the column, for each of the display elements in the column, to the output providing means while a charge from the capacitance storing means is transferred to the first drive line of the EMS device electrically connected to the charge injecting means.

19. The apparatus of claim 18, wherein the first stationary conducting means includes a first stationary electrode layer, the second stationary conducting means includes a second stationary electrode layer, the movable conducting means includes a movable electrode layer, the charge injecting means includes a charge injection circuit, and the selectively electrically connecting means includes a row-select switch.

20. The apparatus of claim 18, further comprising an operational amplifier grounding switch coupled between the output providing means and the input inverting means.

21. The apparatus of claim 18, wherein the movable conducting means of each EMS device includes a first conductor proximal to the first stationary conducting means and a second conductor proximal to the second stationary conducting means, the first conductor connected to the second drive line and electrically insulated from the second conductor, the first conductor and the first stationary conducting means forming the first variable capacitor, the second conductor and the second stationary conducting means forming the second variable capacitor.

22. The apparatus of claim 21, further comprising a storage capacitor having a storage capacitance value, the storage capacitor electrically connected between the first stationary conducting means and the first conductor of the movable conducting means of each of the EMS devices.

23. The apparatus of claim 18, further comprising a bypass capacitor having a bypass capacitance value electrically connected between the input inverting means and the bias voltage line of the bias voltage circuit.

24. The apparatus of claim 18, further comprising a clamping diode electrically connected between the input inverting means and the non-input inverting means.

25. A method of manufacturing, comprising:

providing an array of three terminal electromechanical systems devices arranged in a plurality of rows and columns, each electromechanical systems (EMS) device including;

a first stationary electrode layer connected to a first drive line;

a movable electrode layer connected to a second drive line; and

a second stationary electrode layer connected to a third drive line, the movable electrode layer disposed between the first and the second stationary electrode layers,

wherein a portion of the movable electrode layer and the first stationary electrode layer form a first variable capacitor having a first variable capacitance value, and

wherein a portion of the movable electrode layer and the second stationary electrode layer form a second variable capacitor having a second variable capacitance value;

connecting a bias voltage circuit having a bias voltage line connected to the third drive line of each of the EMS devices in a column of the array, the bias voltage circuit configured to provide a potential difference between the second stationary electrode layer and the movable electrode layer; and

selectively coupling a charge injection circuit to the first drive line and the second drive line of only one of the EMS devices in the column of the array at any one time to provide a desired charge to the first stationary electrode layer, wherein the charge injection circuit includes;

an operational amplifier having an inverting input line, a non-inverting input line, and an output line, the inverting input line of the operational amplifier being electrically connected to the second drive line of each of the EMS devices in the column;

a plurality of row-select switches controlled to selectively electrically connect the output line of the operational amplifier to the first drive line of each of the EMS devices in the column such that the output line of the operational amplifier is electrically connected to the first drive line of only one EMS device at any one time; and

an input capacitor circuit configured to be electrically connected to the inverting line of the operation amplifier or to a voltage circuit for charging the input capacitor circuit to a charge Q_in,

wherein the charge injection circuit is controlled to selectively connect the first drive line of each EMS device in the column, for each of the display elements in the column, to the output line of the operational amplifier while a charge from the input capacitor circuit is transferred to the first drive line of the EMS device electrically connected to the charge injection circuit.

26. The method of claim 25, wherein each of the EMS devices includes an IMOD.

27. The method of claim 25, further comprising connecting a storage capacitor having a storage capacitance value between the first stationary electrode layer and a first conductor of the movable electrode layer of each of the EMS devices, the first conductor being proximal to the first stationary electrode layer.

28. The method of claim 25, further comprising connecting a bypass capacitor having a bypass capacitance value electrically between the inverting line of the operational amplifier and the bias voltage line of the bias voltage circuit.

29. The method of claim 25, further comprising connecting a clamping diode between the inverting line and the non-inverting line of the operational amplifier.

30. A display device manufactured by the method of claim 25.