Orientation stabilization for MEMS devices

• US 20040061925A1
• Filed: 09/30/2002
• Published: 04/01/2004
• Est. Priority Date: 09/30/2002
• Status: Active Grant

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Weingartner, Wendelin, Azarov, Alexei V., Giles, Randy C.
• Granted Patent: US 6,768,571 B2
• Time in Patent Office: Days
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B

Abstract

A control circuit designed to control driving voltages applied to the actuating electrodes of a MEMS mirror. The control circuit is interfaced with a mirror position sensor and includes a variable gain amplifier whose output depends on a desired mirror equilibrium angle and a current mirror tilt angle determined by the sensor. The desired equilibrium angle can be changed by varying a reference signal applied to the amplifier. The control circuit can stabilize the mirror at relatively large tilt angles and, as a result, extend the available angular range beyond the snap-down angle. Since the number of MEMS mirrors that can be arrayed in an optical cross-connect is a function of the available angular range, the number of channels in a cross-connect may be substantially increased.

Claims

1. A method comprising:

receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current position of a movable part of the MEMS device with respect to a stationary part of the MEMS device; and

generating a control signal as a function of the sensor signal, wherein an actuator of the MEMS device achieves a desired position of the movable part with respect to the stationary part based on the control signal.

2. The invention of claim 1, wherein:

the movable part is rotatably coupled to the stationary part;

the sensor signal is indicative of a current rotation angle between the movable and stationary parts;

the control signal is a function of the current rotation angle;

the desired position corresponds to an equilibrium rotation angle between the movable and stationary parts; and

the generating step comprises generating the control signal based on the sensor signal and a reference signal corresponding to the equilibrium rotation angle.

3. The invention of claim 2, further comprising adjusting the reference signal to change the equilibrium rotation angle.

4. The invention of claim 2, wherein the equilibrium rotation angle is greater than or substantially equal to a snap-down angle for the MEMS device.

5. The invention of claim 1, wherein the MEMS device forms part of an optical switch.

6. Apparatus, comprising:

a MEMS device; and

a controller adapted to;

receive, from a position sensor corresponding to the MEMS device, a sensor signal indicative of a current position of a movable part of the MEMS device with respect to a stationary part of the MEMS device; and

generate a control signal as a function of the sensor signal, wherein an actuator of the MEMS device is adapted to achieve a desired position of the movable part with respect to the stationary part based on the control signal.

7. The invention of claim 6, wherein the control signal has a voltage profile, wherein a first portion of the voltage profile has voltage having an absolute value greater than a snap-down voltage for the MEMS device.

8. The invention of claim 7, wherein a second portion of the voltage profile has voltage varying substantially linearly with a current rotation angle between the movable and stationary parts.

9. The invention of claim 7, wherein a second portion of the voltage profile has voltage corresponding to a substantially constant electrostatic torque applied to the movable part with respect to the stationary part.

10. The invention of claim 6, wherein:

the movable part is rotatably coupled to the stationary part;

the sensor signal is indicative of a current rotation angle between the movable and stationary parts;

the control signal is a function of the current rotation angle;

the desired position corresponds to an equilibrium rotation angle between the movable and stationary parts; and

the control circuit is adapted to generate the control signal based on the sensor signal and a reference signal corresponding to the equilibrium rotation angle.

11. The invention of claim 10, wherein an adjustment of the reference signal corresponds to a change in the equilibrium rotation angle.

12. The invention of claim 10, wherein the control circuit comprises a first amplifier adapted to:

receive the reference signal and a fourth signal based on the sensor signal; and

generate a fifth signal, wherein the control signal is based on the fifth signal.

13. The invention of claim 12, wherein the fourth signal is a substantially linear function of the current rotation angle.

14. The invention of claim 12, wherein the control circuit further comprises a second amplifier adapted to amplify the fifth signal to generate the control signal.

15. The invention of claim 12, wherein the first amplifier comprises:

an operational amplifier adapted to operate as an inverting adder; and

a voltage regulator connected to an output of the operational amplifier, wherein;

the operational amplifier is adapted to receive the reference and fourth signals; and

the fifth signal is a regulated output signal of the operational amplifier.

16. The invention of claim 15, wherein the voltage regulator is adapted to clip the output signal of the operational amplifier if the output signal is more negative than a base voltage of the voltage regulator.

17. The invention of claim 10, wherein the equilibrium rotation angle is greater than or substantially equal to a snap-down angle for the MEMS device.

18. The invention of claim 6, wherein the MEMS device forms part of an optical switch.

19. Apparatus, comprising:

means for receiving, from a position sensor corresponding to a MEMS device, a sensor signal indicative of a current position of a movable part of the MEMS device with respect to a stationary part of the MEMS device; and

means for generating a control signal as a function of the sensor signal, wherein an actuator of the MEMS device achieves a desired position of the movable part with respect to the stationary part based on the control signal.