MEMS SENSOR WITH COMPENSATION OF RESIDUAL VOLTAGE

• US 20170168085A1
• Filed: 11/29/2016
• Published: 06/15/2017
• Est. Priority Date: 12/10/2015
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense International, Inc. (TDK Corporation)
• Inventors: Gafforelli, Giacomo, Giambastiani, Adolfo, Coronato, Luca
• Granted Patent: US 10,877,063 B2
• Time in Patent Office: Days
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81C 1/00698 Electrical characteristics, e.g. by doping materials
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A microelectromechanical (MEMS) sensor, such as an accelerometer, has one more proof masses that respond to movement of the sensor, the movement of which is measured based on a distance between the one or more proof masses and on one or more sense electrodes. The accelerometer also has a plurality of auxiliary electrodes and a signal generator configured to apply an auxiliary signal having a first harmonic frequency to the plurality of auxiliary electrodes. Circuitry receives a sensed signal from the plurality of sense electrodes and identifies a portion of the sensed signal having the first harmonic frequency. Based on this identified portion of the sensed signal, the circuitry determines whether a residual voltage is present on the one or more proof masses or on the one or more sense electrodes, and the circuitry modifies the operation of the accelerometer when the residual voltage is determined to be present in order to compensate for the residual voltage.

Claims

1. A method for compensating for a residual voltage on an accelerometer, comprising:

applying, to a plurality of auxiliary electrodes located opposite one or more planar surfaces of one or more proof masses, an auxiliary signal having a first harmonic frequency;

determining, based on a signal from one or more sense electrodes located opposite the one or more planar surfaces, a sensed signal;

identifying, from the sensed signal, a portion of the sensed signal having the first harmonic frequency;

determining, based on the portion of the sensed signal, that the residual voltage is present on the one or more proof masses or on the one or more sense electrodes; and

modifying the operation of the accelerometer based on the determination that the residual voltage is present on the one or more proof masses or on the electrodes.

2. The method of claim 1, wherein determining that the residual voltage is present comprises comparing an amplitude of the portion of the sensed signal to a first threshold.

3. The method of claim 2, wherein the first threshold corresponds to a minimum value at which the residual voltage affects device performance.

4. The method of claim 1, wherein determining that the residual voltage is present comprises comparing an amplitude of the portion of the sensed signal to a plurality of thresholds, and wherein modifying the operation of the accelerometer comprises taking different forms of corrective action based on the largest of the plurality of thresholds that is exceeded.

5. The method of claim 4, wherein the different forms of corrective action comprise changing a scaling factor, applying a compensating voltage at one or more of the plurality of auxiliary electrodes, or applying a compensating voltage at one or more of the one or more sense electrodes.

6. The method of claim 1, further comprising:

applying, at a second time subsequent to the modification, the auxiliary signal;

receiving, at the second time, a second sensed signal based one the auxiliary signal;

identifying, from the second sensed signal, a second portion of the sensed signal having the first harmonic frequency; and

adjusting the modification based on the second portion of the sensed signal.

7. The method of claim 1, wherein the first harmonic frequency is less than half of the resonance frequency for the accelerometer.

8. The method of claim 7, wherein a second harmonic of the first harmonic frequency is less than half of the resonance frequency for the accelerometer.

9. The method of claim 1, wherein the first harmonic frequency is greater than the resonance frequency for the accelerometer.

10. The method of claim 1, wherein both the first harmonic frequency and a second harmonic frequency are more than 5% away from a resonance frequency for the accelerometer.

11. The method of claim 1, wherein the plurality of auxiliary electrodes and the one or more sense electrodes are located on a planar surface of a substrate.

12. The method of claim 11, wherein the one or more proof masses move such that, when at least one of the one or more one or more planar surfaces moves towards the planar surface of the substrate, at least one of the one or more planar surfaces moves in the opposite direction.

13. The method of claim 12, wherein the plurality of auxiliary electrodes comprises two auxiliary electrodes, and wherein the two auxiliary electrodes are located on the planar surface of the substrate facing the one or more planar surfaces of the one or more proof masses.

14. The method of claim 13, wherein the one or more sense electrodes comprise two sense electrodes, and wherein the two sense electrodes are located on the planar surface of the substrate facing the one or more planar surfaces of the one or more proof masses.

15. The method of claim 13, wherein the first auxiliary electrode and the second auxiliary electrode are located relative to the proof mass such that the proof mass is symmetric with respect to the first auxiliary electrode and the second auxiliary electrode, and wherein the auxiliary signal applied to the first auxiliary electrode and the auxiliary signal applied to the second auxiliary electrode are AC differential signals.

16. The method of claim 1, wherein the auxiliary signal applied to a first auxiliary electrode of the plurality of auxiliary electrodes has a first polarity, and wherein the auxiliary signal applied to a second auxiliary electrode of the plurality of auxiliary electrodes has an opposite polarity from the first polarity.

17. An accelerometer, comprising:

one or more proof masses having one or more planar surfaces;

a plurality of auxiliary electrodes located opposite the one or more planar surfaces;

a signal generator configured to apply an auxiliary signal to the plurality of auxiliary electrodes, the auxiliary signal having a first harmonic frequency;

a plurality of sense electrodes located opposite the one or more planar surfaces; and

circuitry coupled to provide a sensed signal based on a signal from the plurality of sense electrodes, wherein the circuitry identifies a portion of the sensed signal having the first harmonic frequency and determines, based on the portion of the sensed signal, that a residual voltage is present on the one or more proof masses or the plurality of sense electrodes, and wherein the circuitry modifies the operation of the accelerometer based on a determination that the residual voltage is present on the one or more proof masses or the plurality of sense electrodes.

18. An accelerometer, comprising:

one or more proof masses having one or more planar surfaces;

a plurality of auxiliary electrodes located opposite the one or more planar surfaces;

a plurality of sense electrodes located opposite the one or more planar surfaces and configured to output a signal representative of a capacitance;

a first signal generator configured to apply an auxiliary signal to the plurality of auxiliary electrodes, the auxiliary signal having a first harmonic frequency;

a second signal generator configured to apply an operating signal to the accelerometer, the operating signal having an operating frequency different than the first harmonic frequency; and

circuitry configured to determine a sensed signal from signal representative of the capacitance, the circuitry configured to identify a first portion of the sensed signal having the first harmonic frequency and to determine, based on the first portion of the sensed signal, that a residual voltage is present on the one or more proof masses or on the plurality of sense electrodes, wherein the circuitry is further configured to compensate for the residual voltage in response to a determination that the residual voltage is present on the one or more proof masses or on the plurality of sense electrodes, and wherein the circuitry is further configured to identify a second portion of the sensed signal having the operating frequency and to determine, based on the second portion of the sensed signal, a linear acceleration for the accelerometer.

19. The accelerometer of claim 18, wherein the operating signal is applied to the plurality of sense electrodes.

20. The accelerometer of claim 18, wherein the operating signal is applied to the one or more proof masses.