Capacitive position sensing for capacitive drive MEMS devices

Patent metadata

Field	Value
Publication number	US-10908361-B2
Application number	US-201816221523-A
Country	US
Kind code	B2
Filing date	Dec 16, 2018
Priority date	Jun 6, 2018
Publication date	Feb 2, 2021
Grant date	Feb 2, 2021

Abstract

An apparatus for driving and position sensing in a comb-drive actuator includes a generator, a driver circuit, sensing circuitry, and signal processing circuitry. The generator is configured to apply a sensing-voltage to a first electrode of the comb-drive actuator. The driver circuit is configured to apply a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode. The sensing circuitry is configured to measure at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode. The signal processing circuitry is configured to estimate a position of the first electrode relative to the second electrode based on the sensed-waveform.

First claim

The invention claimed is:

1. An apparatus for driving and position sensing in a comb-drive actuator, the apparatus comprising:
a generator, configured to apply a sensing-voltage to a first electrode of the comb-drive actuator;
a driver circuit, configured to apply a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode;
sensing circuitry, which is configured to measure at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode; and
signal processing circuitry, which is configured to estimate a position of the first electrode relative to the second electrode based on the sensed-waveform.

2. The apparatus according to claim 1 , wherein the sensed-waveform falls on a resistor connected in series to the second electrode.

3. The apparatus according to claim 1 , wherein the sensed-waveform is measured by a circuit having an adaptive reference ground.

4. The apparatus according to claim 1 , wherein the sensing-voltage comprises a sine waveform.

5. The apparatus according to claim 1 , wherein:
the generator is configured to apply the sensing-voltage to a common first electrode of two or more comb-drive actuators;
the driver circuit comprises two or more driver circuits configured to apply respective drive-voltages to two or more respective second electrodes of the two or more comb-drive actuators;
the sensing circuitry is configured to measure at the second electrodes respective sensed-waveforms resulting from the sensing-voltage applied to the common first electrode; and
the signal processing circuitry is configured to estimate positions of the first electrodes relative to the respective second electrodes based on the respective sensed-waveforms.

6. A method for driving and position sensing in a comb-drive actuator, the method comprising:
applying a sensing-voltage to a first electrode of the comb-drive actuator;
applying a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode;
measuring at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode; and
estimating a position of the first electrode relative to the second electrode based on the sensed-waveform.

7. The method according to claim 6 , wherein measuring the sensed-waveform comprises measuring the sensed-waveform that falls on a resistor connected in series to the second electrode.

8. The method according to claim 6 , wherein measuring the sensed-waveform comprises measuring the sensed-waveform using a circuit having an adaptive reference ground.

9. The method according to claim 6 , wherein applying the sensing-voltage comprises applying a sine waveform.

10. The method according to claim 6 , wherein:
applying the sensing-voltage comprises applying the sensing-voltage to a common first electrode of two or more comb-drive actuators;
applying the drive-voltage comprises applying respective drive-voltages to two or more second electrodes of two or more respective comb-drive actuators;
measuring at the two or more second electrodes respective sensed-waveforms resulting from the sensing-voltage applied to the common first electrode; and
estimating positions of the first electrodes relative to the respective second electrodes based on the sensed-waveforms.

Assignees

• Apple Inc

Inventors

• Fluegel Sebastian
• Sutton Andrew J
• Bradford Bryce T
• Gerson Yuval

Classifications

• G02B26/0841 Primary

  the reflecting element being moved or deformed by electrostatic means · CPC title

• G01B7/003

  for measuring position, not involving coordinate determination (coordinate measuring G01B7/004) · CPC title

• G01P15/125

  by capacitive pick-up · CPC title

• G02B6/357 Primary

  Electrostatic force (electrostatic forces controlling reflecting elements in general G02B26/0841) · CPC title

• G02B6/359

  of the position of the moving element itself during switching, i.e. without monitoring the switched beams · CPC title