Anti-Capture Method and Apparatus for Micromachined Devices

• US 20110221454A1
• Filed: 05/23/2011
• Published: 09/15/2011
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Samuels, Howard R., Hollocher, David C.
• Granted Patent: US 8,917,099 B2
• Time in Patent Office: Days
• US Class Current: 324/661
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 3/0008 Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

A MEMS device has a movable beam, a differential capacitor with a movable electrode that moves in response to the displacement of the movable beam and that is disposed between two stationary electrodes, and a voltage circuit for applying a first voltage to the first stationary electrode, second voltage to the second stationary electrode, and a third voltage to the moveable electrode. The MEMS device also has a monitor operably coupled with the movable beam to monitor the displacement of the movable beam. In some embodiments, the monitor may monitor the distance between the movable electrode and at least one of the stationary electrodes. The MEMS device further has a voltage reducing circuit operatively coupled with the monitor, the movable electrode, and the stationary electrodes. The voltage reducing circuit reduces the differential between the third voltage and the voltages on the stationary electrodes when the monitor detects that the displacement of the movable beam is greater than or equal to a threshold value.

Claims

1. An electrode driver comprising:

a detector for monitoring the output of a MEMS device to determine whether a beam displacement exceeds a threshold distance, the detector having a detector output; and

a driver circuit capable of producing a plurality of electrode drive signals and having a driver circuit input and an electrode driver output, the driver circuit input coupled to the detector output.

2. An electrode driver according to claim 1 wherein the driver circuit comprises a first transistor operably coupled to a first voltage source and a second transistor operably coupled to a second voltage source.

3. An electrode driver according to claim 1, the driver circuit further comprising a selector for operably coupling one of a plurality of electrode drive signals to the electrode driver output in response to the detector output.

4. An electrode driver according to claim 3 wherein the selector comprises a switch.

5. An electrode driver according to claim 3 wherein the selector comprises a transistor.