MEMS gyroscopes with reduced errors

• US 9,212,908 B2
• Filed: 04/26/2012
• Issued: 12/15/2015
• Est. Priority Date: 04/26/2012
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A., Chang, John F.
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): Zhong, Xin
• Application Number:
  US13/456,706
• Publication Number:
  US 20130283908A1
• Time in Patent Office: 1,328 Days
• Field of Search: 735/041.2, 73/13.7, 73/13.8
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/574 the devices having two sensing masses in anti-phase motion
• CPC Class Codes: G01C 19/5755 the devices having a single sensing mass

Abstract

In comb drive vibratory gyroscopes, drive-induced Coriolis accelerometer offset is effectively canceled by demodulating the output during equal times of in-phase and anti-phase drive of the shuttle with respect to the velocity signal used for angular rate demodulation. This reduces or eliminates the corresponding thermal and die-stress effects otherwise needing calibration.

Claims

1. A method of operating vibratory gyroscope having a shuttle and a Coriolis accelerometer, the method comprising:

driving, by a first shuttle driver, vibratory motion of the shuttle using a drive signal having alternating phase and anti-phase drive signal periods; and

demodulating, by a demodulator, output of the Coriolis accelerometer during equal times of phase and anti-phase drive of the shuttle with respect to a velocity signal used for angular rate demodulation.

2. A method according to claim 1, wherein the phase and anti-phase drive signal periods are unequal periods of time.

3. A method according to claim 1, wherein the drive signal is applied such that amplitude of shuttle oscillation does not cross zero during steady state operation.

4. A method according to claim 1, wherein the drive signal is applied such that amplitude of shuttle oscillation periodically crosses zero during steady state operation.

5. A method according to claim 1, wherein the Coriolis accelerometer output is demodulated continually.

6. A method according to claim 1, wherein the Coriolis accelerometer output is demodulated during intervals about the points of greatest shuttle amplitude with blanking between such intervals to discard low amplitude signals and equalize effective up and down periods of demodulation.

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

maintaining phase coherency of the shuttle drive using a phase-locked loop.

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

maintaining phase coherency of the shuttle drive using phase information from a second gyroscope operating in anti-phase with the gyroscope.

9. A method according to claim 1, wherein the equal times of phase and anti-phase drive of the shuttle during which the output of the Coriolis accelerometer is demodulated are centered at the transitions from the phase drive signal period to the anti-phase drive signal period.

10. A method according to claim 1, wherein the vibratory motion of the shuttle is driven using at least one comb drive electrode.

11. A method according to claim 1, wherein the vibratory motion of the shuttle is driven using at least one electrode capacitively coupled with the shuttle.

12. A method according to claim 1, wherein the vibratory motion of the shuttle is driven using at least one piezoelectric electrode.

13. A method according to claim 1, wherein the vibratory motion of the shuttle includes a flexural mode.

14. A method according to claim 1, wherein the vibratory motion of the shuttle includes a bulk acoustic mode.

15. A method according to claim 1, wherein the vibratory motion of the shuttle includes a rotational oscillation.

16. A method according to claim 1, wherein the vibratory motion of the shuttle includes a translational oscillation.

17. A method according to claim 1, wherein the shuttle and the Coriolis accelerometer operate in the same plane.

18. A method according to claim 1, wherein the shuttle and the Coriolis accelerometer operate in different planes.

19. A method according to claim 1, wherein the phase and anti-phase drive signal periods are equal periods of time.

20. A method according to claim 10, wherein the equal periods of time are defined as a predetermined number of shuttle cycles, and wherein the drive signal is applied such that amplitude of shuttle oscillation is continually ramping without reaching a theoretical maximum shuttle amplitude.

27. A gyroscope according to claim 12, wherein:

phase coherency of the shuttle drive is maintained using a phase-locked loop.

28. A gyroscope according to claim 12, further comprising:

a second shuttle; and

a second shuttle driver configured to drive vibratory motion of the second shuttle, wherein the second shuttle driver is configured to operate in anti-phase with the first shuttle driver such that amplitude/velocity of the first shuttle is near its maximum when the amplitude/velocity of the second shuttle is near its minimum and vice versa, and wherein phase coherency of each shuttle/driver is maintained using phase information from the other shuttle/driver.

29. A gyroscope according to claim 12, wherein the equal times of phase and anti-phase drive of the shuttle during which the output of the Coriolis accelerometer is demodulated are centered at the transitions from the phase drive signal period to the anti-phase drive signal period.

21. A gyroscope comprising:

a first shuttle;

a first shuttle driver;

a Coriolis accelerometer; and

a demodulator, wherein the first shuttle driver is configured to drive vibratory motion of the first shuttle using a first drive signal having alternating phase and anti-phase drive signal periods, and wherein the demodulator is configured to demodulate output of the Coriolis accelerometer during equal times of phase and anti-phase drive of the first shuttle with respect to a velocity signal used for angular rate demodulation.

22. A gyroscope according to claim 21, wherein the phase and anti-phase drive signal periods are unequal periods of time.

23. A gyroscope according to claim 21, wherein the drive signal is applied such that amplitude of shuttle oscillation does not cross zero during steady state operation.

24. A gyroscope according to claim 21, wherein the drive signal is applied such that amplitude of shuttle oscillation periodically crosses zero during steady state operation.

25. A gyroscope according to claim 21, wherein the Coriolis accelerometer output is demodulated continually.

26. A gyroscope according to claim 21, wherein the Coriolis accelerometer output is demodulated during intervals about the points of greatest shuttle amplitude with blanking between such intervals to discard low amplitude signals and equalize effective up and down periods of demodulation.

30. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle is driven using at least one comb drive electrode.

31. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle is driven using at least one electrode capacitively coupled with the shuttle.

32. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle is driven using at least one piezoelectric electrode.

33. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle includes a flexural mode.

34. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle includes a bulk acoustic mode.

35. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle includes a rotational oscillation.

36. A gyroscope according to claim 21, wherein the vibratory motion of the shuttle includes a translational oscillation.

37. A gyroscope according to claim 21, wherein the shuttle and the Coriolis accelerometer operate in the same plane.

38. A gyroscope according to claim 21, wherein the shuttle and the Coriolis accelerometer operate in different planes.

39. A gyroscope according to claim 21, wherein the phase and anti-phase drive signal periods are equal periods of time.

40. A gyroscope according to claim 39, wherein the equal periods of time are defined as a predetermined number of shuttle cycles, and wherein the drive signal is applied such that amplitude of shuttle oscillation is continually ramping without reaching a theoretical maximum shuttle amplitude.

41. A gyroscope control circuit for a vibratory gyroscope having a shuttle and a Coriolis accelerometer, the gyroscope control circuit comprising:

a first shuttle driver configured to drive vibratory motion of the shuttle using a first drive signal having alternating phase and anti-phase drive signal periods; and

a demodulator configured to demodulate output of the Coriolis accelerometer during equal times of phase and anti-phase drive of the shuttle with respect to a velocity signal used for angular rate demodulation.

42. A gyroscope control circuit according to claim 41, wherein the phase and anti-phase drive signal periods are unequal periods of time.

43. A gyroscope control circuit according to claim 41, wherein the drive signal is applied such that amplitude of shuttle oscillation does not cross zero during steady state operation.

44. A gyroscope control circuit according to claim 41, wherein the drive signal is applied such that amplitude of shuttle oscillation periodically crosses zero during steady state operation.

45. A gyroscope control circuit according to claim 41, wherein the Coriolis accelerometer output is demodulated continually.

46. A gyroscope control circuit according to claim 41, wherein the Coriolis accelerometer output is demodulated during intervals about the points of greatest shuttle amplitude with blanking between such intervals to discard low amplitude signals and equalize effective up and down periods of demodulation.

47. A gyroscope control circuit according to claim 41, wherein phase coherency of the shuttle drive is maintained using a phase-locked loop.

48. A gyroscope control circuit according to claim 41, wherein phase coherency of the shuttle drive is maintained using phase information from a second gyroscope operating in anti-phase with the gyroscope.

49. A gyroscope control circuit according to claim 41, wherein the equal times of phase and anti-phase drive of the shuttle during which the output of the Coriolis accelerometer is demodulated are centered at the transitions from the phase drive signal period to the anti-phase drive signal period.

50. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle is driven using at least one comb drive electrode.

51. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle is driven using at least one electrode capacitively coupled with the shuttle.

52. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle is driven using at least one piezoelectric electrode.

53. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle includes a flexural mode.

54. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle includes a bulk acoustic mode.

55. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle includes a rotational oscillation.

56. A gyroscope control circuit according to claim 41, wherein the vibratory motion of the shuttle includes a translational oscillation.

57. A gyroscope control circuit according to claim 41, wherein the shuttle and the Coriolis accelerometer operate in the same plane.

58. A gyroscope control circuit according to claim 41, wherein the shuttle and the Coriolis accelerometer operate in different planes.

59. A gyroscope control circuit according to claim 41, wherein the phase and anti-phase drive signal periods are equal periods of time.

60. A gyroscope control circuit according to claim 59, wherein the equal periods of time are defined as a predetermined number of shuttle cycles, and wherein the drive signal is applied such that amplitude of shuttle oscillation is continually ramping without reaching a theoretical maximum shuttle amplitude.

61. A gyroscope comprising:

means for driving vibratory motion of a shuttle using a drive signal having alternating phase and anti-phase drive signal periods; and

means for demodulating output of a Coriolis accelerometer during equal times of phase and anti-phase drive of the shuttle with respect to a velocity signal used for angular rate demodulation.