Mode-matching apparatus and method for micromachined inertial sensors

• US 8,616,055 B2
• Filed: 04/09/2012
• Issued: 12/31/2013
• Est. Priority Date: 05/21/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A.
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US13/442,010
• Publication Number:
  US 20120192648A1
• Time in Patent Office: 631 Days
• Field of Search: 73/13.8, 735/041.2, 735/041.3, 735/041.4, 735/09, 735/10, 735/140.1, 735/140.2
• 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

In an inertial sensor having a resonator and an accelerometer, acceleration signals are induced by resonating at least one shuttle of the resonator in a device plane at a shuttle resonance mode frequency and modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer. The motion may be modulated in the device plane or out of the device plane. A shuttle resonance mode and an accelerometer resonance mode may me matched based on the induced accelerometer signals, for example, by providing a feedback signal to the inertial sensor in response to such induced accelerometer signals to substantially nullify the induced accelerometer signals.

Claims

1. A method of inducing acceleration signals 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 accelerometer signals from the accelerometer, wherein 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.

2. A method according to claim 1, wherein the accelerometer signals are electromechanically modulated accelerometer signals.

3. A method according to claim 1, wherein the motion is modulated outside of the device plane.

4. A method according to claim 1, wherein the motion is modulated in the device plane.

5. 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;

or

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

6. A method according to claim 1, further comprising:

matching a shuttle resonance mode and an accelerometer resonance mode based on the induced accelerometer signals.

7. A method according to claim 6, wherein modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer comprises providing 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.

8. A method according to claim 7, wherein matching the shuttle resonance mode and the accelerometer resonance mode based on the induced accelerometer signals comprises:

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

9. An inertial sensor comprising:

an accelerometer characterized by an accelerometer resonance mode;

a resonator including at least one shuttle configured to resonate in a device plane;

a shuttle resonance drive servo configured to provide a drive signal, the drive signal resonating the at least one shuttle in the device plane at a shuttle resonance mode frequency; and

a test signal generator configured to provide a test signal, the test signal modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer, wherein the test signal is applied to a variable-overlap electrode associated with the at least one shuttle.

10. An inertial sensor according to claim 9, wherein the accelerometer signals are electromechanically modulated accelerometer signals.

11. An inertial sensor according to claim 9, wherein the motion is modulated outside of the device plane.

12. An inertial sensor according to claim 9, wherein the motion is modulated in the device plane.

13. An inertial sensor according to claim 9, 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;

or

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

14. An inertial sensor according to claim 9, further comprising:

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.

15. An inertial sensor according to claim 14, wherein the test signal generator is configured to provide the 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.

16. An inertial sensor according to claim 15, wherein the mode matching servo is configured to provide a feedback signal to the inertial sensor in response to such induced accelerometer signals to substantially nullify the induced accelerometer signals.

17. A method of inducing acceleration signals 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;

modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer; and

matching a shuttle resonance mode and an accelerometer resonance mode based on the induced accelerometer signals.

18. A method according to claim 17, wherein the accelerometer signals are electromechanically modulated accelerometer signals.

19. A method according to claim 17, wherein the motion is modulated outside of the device plane.

20. A method according to claim 17, wherein the motion is modulated in the device plane.

21. A method according to claim 17, wherein 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.

22. A method according to claim 17, wherein modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer comprises providing 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.

23. A method according to claim 22, wherein matching the shuttle resonance mode and the accelerometer resonance mode based on the induced accelerometer signals comprises:

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

24. A method according to claim 22, wherein providing the feedback signal comprises:

demodulating accelerometer signals against a quadrature signal to produce a modulated quadrature signal;

demodulating the modulated quadrature signal against a product of the test signal with a shuttle frequency signal to produce an error signal; and

producing the feedback signal based on the error signal.

25. A method according to claim 22, wherein, providing the feedback signal comprises at least one of:

placing a bias voltage on the at least one shuttle;

placing a bias voltage on a quadrature adjusting electrode;

or

placing a bias voltage on a separate mode adjusting electrode.

26. An inertial sensor comprising:

an accelerometer characterized by an accelerometer resonance mode;

a resonator including at least one shuttle configured to resonate in a device plane;

a shuttle resonance drive servo configured to provide a drive signal, the drive signal resonating the at least one shuttle in the device plane at a shuttle resonance mode frequency;

a test signal generator configured to provide a test signal, the test signal modulating the motion of the at least one resonator shuttle to induce accelerometer signals from the accelerometer; 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.

27. An inertial sensor according to claim 26, wherein the accelerometer signals are electromechanically modulated accelerometer signals.

28. An inertial sensor according to claim 26, wherein the motion is modulated outside of the device plane.

29. An inertial sensor according to claim 26, wherein the motion is modulated in the device plane.

30. An inertial sensor according to claim 26, wherein the test signal is applied to a variable-overlap electrode associated with the at least one shuttle.

31. An inertial sensor according to claim 26, wherein the test signal generator is configured to provide the 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.

32. A method according to claim 26, wherein the mode matching servo comprises:

a mode matching servo demodulator configured to demodulate a modulated quadrature signal with the test signal to produce an error signal; and

a mode matching servo integrator configured to remove accelerometer signals from the error signal and magnify the error signal to produce the feedback signal.

33. A method according to claim 26, wherein, the feedback signal is provided to at least one of:

the at least one shuttle;

a quadrature adjusting electrode;

or

a separate mode adjusting electrode.