Offset detection and compensation for micromachined inertial sensors

• US 8,783,103 B2
• Filed: 08/21/2009
• Issued: 07/22/2014
• Est. Priority Date: 08/21/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Clark, William A., Geen, John A.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US12/545,334
• Publication Number:
  US 20110041609A1
• Time in Patent Office: 1,796 Days
• Field of Search: 73/13.7, 73/13.8, 735/041.2
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

Error sources relating to the drive signal applied to the resonator of an inertial sensor, such as in-phase offset errors relating to the drive signal and/or electronic pass-through of the drive signal to accelerometer sense electronics, are detected by modulating the drive signal and sensing accelerometer signals that are induced by the modulated drive signal. Error sources related to aerodynamics of an inertial sensor resonator are detected by modulating the distance between the resonator and the underlying substrate and sensing accelerometer signals that are induced by such modulation. Compensating signals may be provided to substantially cancel errors caused by such error sources.

Claims

1. A method of detecting at least one error source relating to the magnitude of a drive signal applied to the resonator in an inertial sensor having a resonator and an accelerometer for measuring a Coriolis acceleration signal in a Coriolis acceleration signal band of a Coriolis channel, wherein the at least one error source induces corresponding error signals in the Coriolis channel that are in-phase with the drive signal and include error signals that affect the Coriolis acceleration signal, the method comprising:

providing a modulated drive signal to the resonator, the modulated drive signal modulating the magnitude of the drive force applied to the resonator so as to modulate the magnitude of the at least one error source so as to induce corresponding modulated error signals in the Coriolis channel, wherein the error signals are modulated at a frequency outside of the Coriolis acceleration signal band;

sensing the modulated error signals in the Coriolis channel; and

providing at least one compensating signal responsive to the sensed modulated error signals to substantially cancel errors introduced by the at least one error source that affect the Coriolis acceleration signal.

2. A method according to claim 1, wherein providing the modulated drive signal to the resonator comprises:

modulating a drive signal using one of amplitude modulation, frequency modulation, on/off keying, or a spread spectrum modulation.

3. A method according to claim 1, wherein sensing modulated error signals induced by the modulated drive signal includes demodulating accelerometer signals based on a modulation signal used to modulate the drive signal.

4. A method according to claim 1, wherein the at least one error source includes in-phase offset error that is substantially in-phase with the modulated drive signal, and wherein providing at least one compensating signal responsive to the sensed accelerometer signals comprises providing at least one compensating signal to substantially cancel the in-phase offset error.

5. A method according to claim 4,

wherein providing at least one compensating signal to substantially cancel the in-phase offset error comprises providing a compensating signal to a set of in-phase-compensating electrodes to substantially cancel the in-phase offset error.

6. A method according to claim 4, wherein the at least one error source includes drive force misalignment.

7. A method according to claim 1, wherein the at least one error source includes electronic pass-through of the drive signal to the accelerometer, and wherein providing at least one compensating signal responsive to the sensed modulated error signals comprises providing at least one compensating signal to substantially cancel the pass-through.

8. A method according to claim 7,

wherein providing at least one compensating signal to substantially cancel the pass-through comprises providing a compensating signal to the accelerometer to substantially cancel the pass-through.

9. A method according to claim 1, wherein the resonator includes a plurality of shuttles coupled to resonate at a single resonance frequency.

10. A method according to claim 1, wherein the accelerometer includes at least one of:

a sense electrode in a plane of the resonator;

or

a sense electrode out of the plane of the resonator.

11. An inertial sensor comprising:

a resonator;

an accelerometer for measuring a Coriolis acceleration signal in a Coriolis acceleration signal band of a Coriolis channel, wherein the at least one error source induces corresponding error signals in the Coriolis channel that are in-phase with the drive signal and include error signals that affect the Coriolis acceleration signal;

a resonator driver configured to provide a modulated drive signal to the resonator, the modulated drive signal modulating the magnitude of the drive force applied to the resonator so as to modulate the magnitude of the at least one error source so as to induce corresponding modulated error signals in the Coriolis channel, wherein the error signals are modulated at a frequency outside of the Coriolis acceleration signal band;

an offset detector configured to sense the modulated error signals in the Coriolis channel; and

a servo configured to provide at least one compensating signal responsive to the sensed modulated error signals to substantially cancel errors introduced by the at least one error source that affect the Coriolis acceleration signal.

12. An inertial sensor according to claim 11, wherein the resonator driver is configured to modulate the drive signal using one of amplitude modulation, frequency modulation, on/off keying, or a spread spectrum modulation.

13. An inertial sensor according to claim 11, wherein the offset detector is configured to demodulate accelerometer signals based on a modulation signal used to modulate the drive signal to sense modulated error signals induced by the modulated drive signal.

14. An inertial sensor according to claim 11, wherein the at least one error source includes in-phase offset error that is substantially in-phase with the modulated drive signal, and wherein the servo is configured to provide at least one compensating signal responsive to the sensed accelerometer signals to substantially cancel the in-phase offset error.

15. An inertial sensor according to claim 14, wherein the servo is configured to provide a compensating signal to a set of in-phase-compensating electrodes to substantially cancel the in-phase offset error.

16. An inertial sensor according to claim 14, wherein the at least one error source includes drive force misalignment.

17. An inertial sensor according to claim 11, wherein the at least one error source includes electronic pass-through of the drive signal to the accelerometer, and wherein the servo is configured to provide at least one compensating signal responsive to the sensed modulated error signals to substantially cancel the pass-through.

18. An inertial sensor according to claim 17, wherein the servo is configured to provide a compensating signal to the accelerometer to substantially cancel the pass-through.

19. An inertial sensor according to claim 11, wherein the resonator includes a plurality of shuttles coupled to resonate at a single resonance frequency.

20. An inertial sensor according to claim 11, wherein the accelerometer includes at least one of:

a sense electrode in a plane of the resonator;

or

a sense electrode out of the plane of the resonator.

21. A controller for detecting at least one error source relating to the magnitude of a drive signal applied to a resonator of an inertial sensor including the resonator and an accelerometer for measuring a Coriolis acceleration signal in a Coriolis acceleration signal band of a Coriolis channel, wherein the at least one error source induces corresponding error signals in the Coriolis channel that are in-phase with the drive signal and include error signals that affect the Coriolis acceleration signal, the controller comprising:

a resonator driver configured to provide a modulated drive signal to the resonator, the modulated drive signal modulating the magnitude of the drive force applied to the resonator so as to modulate the magnitude of the at least one error source so as to induce corresponding modulated error signals in the Coriolis channel, wherein the error signals are modulated at a frequency outside of the Coriolis acceleration signal band;

an offset detector configured to sense the modulated error signals in the Coriolis channel; and

a servo configured to provide at least one compensating signal responsive to the sensed accelerometer signals to the inertial sensor to substantially cancel errors introduced by the at least one error source that affect the Coriolis acceleration signal.

22. A controller according to claim 21, wherein the resonator driver is configured to modulate the drive signal using one of amplitude modulation, frequency modulation, on/off keying, or a spread spectrum modulation.

23. A controller according to claim 21, wherein the offset detector is configured to demodulate accelerometer signals based on a modulation signal used to modulate the drive signal to sense modulated error signals induced by the modulated drive signal.

24. A controller according to claim 21, wherein the at least one error source includes in-phase offset error that is substantially in-phase with the modulated drive signal, and wherein the servo is configured to provide at least one compensating signal responsive to the sensed modulated error signals to substantially cancel the in-phase offset error.

25. A controller according to claim 24, wherein the servo is configured to provide a compensating signal to a set of in-phase-compensating electrodes to substantially cancel the in-phase offset error.

26. A controller according to claim 24, wherein the at least one error source includes drive force misalignment.

27. A controller according to claim 21, wherein the at least one error source includes electronic pass-through of the drive signal to the accelerometer, and wherein the servo is configured to provide at least one compensating signal responsive to the sensed accelerometer signals to substantially cancel the pass-through.

28. A controller according to claim 27, wherein the servo is configured to provide a compensating signal to the accelerometer to substantially cancel the pass-through.