Mode-Matching Apparatus and Method for Micromachined Inertial Sensors

• US 20100294039A1
• Filed: 05/21/2009
• Published: 11/25/2010
• Est. Priority Date: 05/21/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A.
• Granted Patent: US 8,151,641 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• 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: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719

Abstract

A mode matching servo for an inertial sensor having a resonator and an accelerometer provides a test signal at a frequency higher than a predetermined inertial sensor response frequency and lower than an accelerometer resonance mode frequency so as to induce acceleration signals from the accelerometer substantially at the test signal frequency when the modes are not matched. A feedback signal is provided in response to such induced signals to substantially nullify the signals.

Claims

1. In an inertial sensor having a resonator and an accelerometer, the resonator including at least one shuttle characterized by a shuttle resonance mode, the accelerometer characterized by an accelerometer resonance mode, a method of matching the shuttle resonance mode and the accelerometer resonance mode, the method comprising:

providing a test signal to the inertial sensor at a frequency higher than a predetermined inertial sensor response frequency and lower than a predetermined accelerometer resonance mode frequency, the test signal inducing accelerometer signals when the shuttle resonance mode and the accelerometer resonance mode are not matched; and

providing a feedback signal to the inertial sensor in response to such induced accelerometer signals to substantially nullify the induced accelerometer signals.

2. A method according to claim 1, wherein the test signal modulates the motion of the at least one shuttle to induce the accelerometer signals.

3. A method according to claim 2, wherein the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle outside of the device plane, and the bias signal produces a force outside of the device plane.

4. A method according to claim 3, wherein providing the test signal comprises:

applying the test signal to a set of variable-overlap electrodes underlying the at least one shuttle.

5. A method according to claim 2, wherein the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle in the device plane, and the bias signal produces a force in the device plane.

6. A method according to claim 5, wherein providing the test signal comprises:

applying the test signal to a set of variable-overlap electrodes adjacent to the at least one shuttle.

7. A method according to claim 1, wherein at least one of:

the test signal frequency is an integer fraction of the shuttle resonance mode frequency;

the test signal is a zero-average test signal; and

the test signal causes alternating movements of the at least one shuttle in two substantially equal but opposite directions.

8. A method according to claim 1, wherein the resonator includes a plurality of shuttles that operate substantially at a single shuttle resonance mode frequency.

9. A method according to claim 8, wherein the resonator includes at least one pair of shuttles coupled to resonate rotationally in anti-phase with one another.

10. A method according to claim 1, wherein providing the feedback signal to the inertial sensor comprises applying a bias voltage to one of (1) the at least one shuttle;

(2) a set of quadrature adjusting electrodes; and

(3) a separate set of mode adjusting electrodes.

11. A method according to claim 1, wherein providing the test signal comprises applying the test signal to a set of quadrature adjusting electrodes.

12. An inertial sensor comprising:

an accelerometer characterized by an accelerometer resonance mode;

a resonator including at least one shuttle characterized by a shuttle resonance mode;

a test signal generator configured to provide a test signal at a frequency higher than a predetermined inertial sensor response frequency and lower than a predetermined accelerometer resonance mode frequency, the test signal inducing accelerometer signals when the shuttle resonance mode and the accelerometer resonance mode are not matched; and

a mode matching servo for matching the shuttle resonance mode and the accelerometer resonance mode, the servo configured to provide a feedback signal to the inertial sensor in response to such induced accelerometer signals to substantially nullify the induced accelerometer signals.

13. An inertial sensor according to claim 12, wherein the test signal modulates the motion of the at least one shuttle to induce the accelerometer signals.

14. An inertial sensor according to claim 13, wherein the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle outside of the device plane, and the bias signal produces a force outside of the device plane.

15. An inertial sensor according to claim 14, wherein providing the test signal comprises:

applying the test signal to a set of variable-overlap electrodes underlying the at least one shuttle.

16. An inertial sensor according to claim 13, wherein the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle in the device plane, and the bias signal produces a force in the device plane.

17. An inertial sensor according to claim 16, wherein providing the test signal comprises:

applying the test signal to a set of variable-overlap electrodes adjacent to the at least one shuttle.

18. An inertial sensor according to claim 12, wherein at least one of:

the test signal frequency is an integer fraction of the shuttle resonance mode frequency;

the test signal is a zero-average test signal; and

the test signal causes alternating movements of the at least one shuttle in two substantially equal but opposite directions.

19. An inertial sensor according to claim 12, wherein the resonator includes a plurality of shuttles that operate substantially at a single shuttle resonance mode frequency.

20. An inertial sensor according to claim 19, wherein the resonator includes at least one pair of shuttles coupled to resonate rotationally in anti-phase with one another.

21. An inertial sensor according to claim 12, wherein the feedback signal is a bias voltage applied to one of (1) the at least one shuttle;

(2) a set of quadrature adjusting electrodes; and

(3) a separate set of mode adjusting electrodes.

22. An inertial sensor according to claim 12, wherein the test signal is applied to a set of quadrature adjusting electrodes.

23. An inertial sensor according to claim 12, wherein the resonator further includes a plurality of shuttle drivers oriented along radial spokes of the at least one shuttle for rotationally resonating the at least one shuttle, and wherein the accelerometer includes a plurality of acceleration sensor electrodes positioned so as to be unaligned with the spokes.

24. An inertial sensor according to claim 12, wherein the at least one shuttle includes a plurality of plates, each plate completely overlaying a corresponding acceleration sensor electrode on an underlying substrate and partially overlaying a pair of quadrature electrodes on opposite sides of the acceleration sensor electrode on the underlying substrate, such that capacitive coupling between the plate and each of the quadrature electrodes is dependent upon the rotational position of the at least one shuttle while capacitive coupling between the plate and the acceleration sensor electrode is substantially independent of the rotational position of the at least one shuttle.

25. A controller for matching a shuttle resonance mode and an accelerometer resonance mode for an inertial sensor having a resonator and an accelerometer, the controller comprising:

a test signal generator configured to provide a test signal at a frequency higher than a predetermined inertial sensor response frequency and lower than a predetermined accelerometer resonance mode frequency, the test signal inducing accelerometer signals when the shuttle resonance mode and the accelerometer resonance mode are not matched; and

a mode matching servo configured to provide a feedback signal to the inertial sensor in response to such induced accelerometer signals to substantially nullify the induced accelerometer signals.

26. An inertial sensor comprising:

a substrate having a plurality of electrode arrangements, each electrode arrangement including an acceleration sensor electrode and a pair of quadrature electrodes on opposite sides of the acceleration sensor electrode; and

a resonator disposed above the substrate and having at least one shuttle including a plurality of plates, each plate completely overlaying a corresponding acceleration sensor electrode and partially overlaying the pair of quadrature electrodes on opposite sides of the acceleration sensor electrode, such that capacitive coupling between the plate and each of the quadrature electrodes is dependent upon the rotational position of the at least one shuttle while capacitive coupling between the plate and the acceleration sensor electrodes is substantially independent of the rotational position of the at least one shuttle.

27. An inertial sensor according to claim 26, wherein each electrode arrangement further includes a phase-compensating electrode.

28. A method of inducing acceleration signals for matching a shuttle resonance mode and an accelerometer resonance mode in an inertial sensor having a resonator and an accelerometer, the resonator including at least one shuttle, the method comprising:

resonating the at least one shuttle in a device plane at a shuttle resonance mode frequency; and

modulating the motion of the at least one resonator shuttle to induce the accelerometer signals.

29. A method according to claim 28, wherein at least one of:

the accelerometer signals are electromechanically modulated accelerometer signals;

the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle outside of the device plane, and the bias signal produces a force outside of the device plane;

the at least one shuttle resonates in a device plane, the test signal modulates the motion of the at least one shuttle in the device plane, and the bias signal produces a force in the device plane; and

modulating the motion of the at least one resonator shuttle comprises applying a test signal to a variable-overlap electrode associated with the at least one shuttle.