Microelectromechanical gyroscope with position control driving and method for controlling a microelectromechanical gyroscope

• US 8,375,789 B2
• Filed: 06/02/2010
• Issued: 02/19/2013
• Est. Priority Date: 06/03/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Prandi, Luciano, Caminada, Carlo
• Primary Examiner(s): Kwok, Helen C.
• Application Number:
  US12/792,599
• Publication Number:
  US 20100307243A1
• Time in Patent Office: 993 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.2, 735/041.4, 735/041.5, 735/041.6, 73/17.7
• 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 19/5726 Signal processing
• CPC Class Codes: G01C 19/5762 the sensing mass being connected to a driving mass, e.g. driving frames
• CPC Class Codes: H03F 3/70 Charge amplifiers

Abstract

A MEMS gyroscope includes: a microstructure having a fixed structure, a driving mass, movable with respect to the fixed structure according to a driving axis, and a sensing mass, mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass according to a sensing axis, in response to rotations of the microstructure; and a driving device, for keeping the driving mass in oscillation with a driving frequency. The driving device includes a discrete-time sensing interface, for detecting a position of the driving mass with respect to the driving axis and a control stage for controlling the driving frequency on the basis of the position of the driving mass.

Claims

1. A microelectromechanical gyroscope comprising:

a microstructure including a fixed structure, a driving mass, movable with respect to the fixed structure with a first degree of freedom according to a driving axis, and a first sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a second degree of freedom according to a first sensing axis in response to rotations of the microstructure; and

a sensing device forming a microelectromechanical loop with the microstructure, the microelectromechanical loop being configured to keep the driving mass in oscillation according to the driving axis at a driving frequency;

wherein the sensing device comprises;

a discrete-time sensing interface coupled to the microstructure and configured to sense a discrete-time position of the driving mass with respect to the driving axis, the sensing interface including a discrete-time charge amplifier configured to sense the discrete-time position of the driving mass and provide a discrete-time detection signal that indicates the discrete-time position of the driving mass; and

a controller configured to control an oscillation amplitude of the microelectromechanical loop based on the discrete-time detection signal that indicates the discrete-time position of the driving mass.

2. A gyroscope according to claim 1, wherein the discrete-time charge amplifier is a discrete-time fully-differential charge amplifier.

3. A gyroscope according to claim 2, wherein the microstructure includes feedback sensing terminals capacitively coupled to the driving mass and the charge amplifier has inputs respectively coupled to the feedback sensing terminals.

4. A gyroscope according to claim 1, wherein the charge amplifier comprises:

a fully-differential operational amplifier having first and second inputs and first and second outputs;

a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and

a second amplification capacitor coupled between the second input and the second output of the operational amplifier.

5. A gyroscope according to claim 4, wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier.

6. A gyroscope according to claim 5, wherein the CDS stage comprises;

a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;

a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;

a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and

a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.

7. A gyroscope according to claim 6, wherein the CDS switches are configured to be controlled so as to be closed in an offset sampling step and open in a sensing step of a correlated double sampling cycle.

8. A gyroscope according to claim 7, wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in the offset sampling step and in the sensing step.

9. A gyroscope according to claim 1, wherein the controller comprises a phase shift module cascaded to the charge amplifier and configured to receive the discrete-time detection signal and produce a continuous-time phase-shifted detection signal having a phase shift in a range of 90°

±

40°

.

10. A gyroscope according to claim 9, wherein the controller comprises a low-pass filter arranged downstream of the phase shift module, having a passband that includes the driving frequency, and configured to reduce from the continuous-time, phase-shifted detection signal undesired signal components at least 30 dB.

11. A gyroscope according to claim 10, wherein the controller comprises:

a variable gain amplifier configured to produce a continuous-time driving signal based on the continuous-time, phase-shifted detection signal and drive the driving mass with the continuous-time driving signal; and

a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the microelectromechanical loop.

12. A gyroscope according to claim 1, comprising a first discrete-time reading device coupled to the microstructure and configured to sense displacements of the first sensing mass according to the sensing axis.

13. A gyroscope according to claim 12, wherein the controller includes:

synchronization means for detecting an oscillation phase of the microelectromechanical loop; and

a phase generator stage configured to be controlled by the synchronization means, generate a reading signal having a frequency that is multiple of the driving frequency, and transmit the reading signal to the driving mass and the first sensing mass.

14. A gyroscope according to claim 12, comprising:

a second sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a third degree of freedom according to a second sensing axis independent from the first sensing axis, in response to rotations of the microstructure; and

a second discrete-time reading device coupled to the microstructure and configured to sense displacements of the second sensing mass according to the second sensing axis.

15. A method, comprising:

controlling a microelectromechanical gyroscope provided with a microstructure that includes a fixed structure, a driving mass, movable with respect to the fixed structure with a first degree of freedom according to a driving axis, and a sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a second degree of freedom according to a sensing axis, in response to rotations of the microstructure, the controlling including;

discrete-time sensing a discrete-time position of the driving mass with respect to the driving axis, the discrete-time sensing including producing a discrete-time detection signal that indicates the discrete-time position of the driving mass;

converting the discrete-time detection signal to a continuous-time detection signal; and

controlling an oscillation amplitude of the driving mass based on the continuous-time detection signal.

16. A method according to claim 15, wherein the sensing comprises a sensing using a discrete-time fully-differential charge amplifier that produces the discrete-time detection signal.

17. A method according to claim 15, comprising sensing displacements of the sensing mass according to the sensing axis.

18. A method according to claim 17, comprising:

detecting an oscillation phase of a microelectromechanical loop that includes the driving mass;

generating a reading signal based on the detected oscillation phase, the reading signal having a frequency that is a multiple of the driving frequency, and

transmitting the reading signal to the driving mass and the sensing mass.

19. A system comprising:

a control unit; and

a microelectromechanical gyroscope coupled to the control unit and configured to be controlled by the control unit, the gyroscope including;

a microstructure including a fixed structure, a driving mass, movable with respect to the fixed structure with a first degree of freedom according to a driving axis, and a first sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a second degree of freedom according to a first sensing axis in response to rotations of the microstructure; and

a sensing device forming a microelectromechanical loop with the microstructure, the microelectromechanical loop being configured to keep the driving mass in oscillation according to the driving axis at a driving frequency;

wherein the sensing device comprises;

a discrete-time sensing interface coupled to the microstructure and configured to sense a discrete-time position of the driving mass with respect to the driving axis, the sensing interface including a discrete-time charge amplifier configured to sense the discrete-time position and provide a discrete-time detection signal that indicates the discrete-time position of the driving mass; and

a controller configured to control an oscillation amplitude of the microelectromechanical loop based on the discrete-time detection signal that indicates the discrete-time position of the driving mass.

20. A system according to claim 19, wherein the charge amplifier comprises:

a fully-differential operational amplifier having first and second inputs and first and second outputs;

a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and

a second amplification capacitor coupled between the second input and the second output of the operational amplifier.

21. A system according to claim 20, wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier.

22. A system according to claim 21, wherein the CDS stage comprises;

a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;

a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;

a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and

a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.

23. A system according to claim 22, wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in an offset sampling step and in a sensing step.

24. A system according to claim 19, wherein the controller comprises a phase shift module cascaded to the charge amplifier and configured to receive the discrete-time detection signal and produce a continuous-time phase-shifted detection signal having a phase shift in a range of 90°

±

40°

.

25. A system according to claim 19, wherein the controller comprises:

a variable gain amplifier configured to produce a continuous-time driving signal based on the continuous-time, phase-shifted detection signal and drive the driving mass with the continuous-time driving signal; and

a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the microelectromechanical loop.

26. A system according to claim 19, wherein the gyroscope comprises:

a second sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a third degree of freedom according to a second sensing axis independent from the first sensing axis, in response to rotations of the microstructure; and

a discrete-time reading device coupled to the microstructure and configured to sense displacements of the second sensing mass according to the second sensing axis.

27. A sensing device for a microstructure that includes a fixed structure, a driving mass, movable with respect to the fixed structure with a first degree of freedom according to a driving axis, and a sensing mass mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass with a second degree of freedom according to a sensing axis in response to rotations of the microstructure, the sensing device comprising:

a discrete-time sensing interface configured to sense a discrete-time position of the driving mass with respect to the driving axis and produce a discrete-time detection signal that indicates the discrete-time position of the driving mass;

a converter configured to convert the discrete-time detection signal to a continuous-time detection signal; and

a driving amplifier coupled to the converter and configured to control an oscillation amplitude of the driving mass based on the continuous-time detection signal.

28. A sensing device according to claim 27, wherein the sensing interface comprises a discrete-time fully-differential charge amplifier configured to produce the discrete-time detection signal.

29. A sensing device according to claim 28, wherein the charge amplifier has first and second inputs and first and second outputs, and the sensing interface comprises:

a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and

a second amplification capacitor coupled between the second input and the second output of the operational amplifier.

30. A sensing device according to claim 29, wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier, the CDS stage including:

a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;

a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;

a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and

a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.

31. A sensing device according to claim 30, wherein the CDS switches are configured to be controlled so as to be closed in an offset sampling step and open in a sensing step of a correlated double sampling cycle.

32. A sensing device according to claim 31, wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in the offset sampling step and in the sensing step.

33. A sensing device according to claim 27, wherein the converter includes a phase shift module coupled between the sensing interface and the driving amplifier and configured to convert the discrete-time detection signal to a continuous-time detection signal and introduce a phase shift in a range of 90°

±

40°

.

34. A sensing device according to claim 27, further comprising a low-pass filter coupled between the sensing interface and the driving amplifier, having a passband that includes a driving frequency, and configured to reduce undesired signal components at least 30 dB.

35. A sensing device according to claim 27, wherein the driving amplifier is a variable gain amplifier, the sensing device further comprising a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the driving mass.