Microelectromechanical gyroscope with continuous self-test function

• US 8,459,093 B2
• Filed: 12/20/2010
• Issued: 06/11/2013
• Est. Priority Date: 12/21/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Donadel, Andrea, Prandi, Luciano, Caminada, Carlo
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US12/973,636
• Publication Number:
  US 20110146402A1
• Time in Patent Office: 904 Days
• Field of Search: 73/13.7, 735/041.2
• US Class Current: 73/1.37
• 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: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A microelectromechanical gyroscope includes a body and a sensing mass, which is movable with a degree of freedom in response to rotations of the body about an axis. A self-test actuator is capacitively coupled to the sensing mass for supplying a self-test signal. The capacitive coupling causes, in response to the self-test signal, electrostatic forces that are able to move the sensing mass in accordance with the degree of freedom at an actuation frequency. A sensing device detects transduction signals indicating displacements of the sensing mass in accordance with the degree of freedom. The sensing device is configured for discriminating, in the transduction signals, spectral components that are correlated to the actuation frequency and indicate the movement of the sensing mass as a result of the self-test signal.

Claims

1. A microelectromechanical gyroscope, comprising:

a body;

a sensing mass, elastically coupled to the body and movable with respect to the body according to a degree of freedom in response to rotations of the body about a sensing axis;

a self-test actuator configured to produce a self-test signal, the self-test actuator including;

a modulator having a first input configured to receive a base-band signal and a second input configured to receive a carrier signal, the modulator being configured to generate the self-test signal by modulation of the carrier signal with the base-band signal;

a capacitive coupling that couples the self-test actuator to the sensing mass and is configured to apply, in response to a self-test signal from the self-test actuator, electrostatic forces to move the sensing mass in accordance with the degree of freedom and at an actuation frequency; and

a sensing device configured to sense transduction signals indicative of displacements of the sensing mass according to the degree of freedom, and to discriminate, in the transduction signals, spectral components corresponding to the actuation frequency and spectral components indicative of motion of the sensing mass caused by the rotation of the body, the sensing device including;

a signal demodulator having a demodulation input configured to receive the carrier signal and a transduction signal input coupled to the sensing mass and configured to receive the transduction signals, the signal demodulator being configured to generate first demodulated signals by demodulation of the transduction signals with the carrier signal; and

a self-test demodulator having a signal input coupled to the signal demodulator and configured to receive the first demodulated signals and a demodulation input configured to receive the base-band signal, the self-test demodulator being configured to generate second demodulated signals by demodulation of the first demodulated signals with the base-band signal.

2. The gyroscope according to claim 1, comprising:

a driving mass, elastically coupled to the body to be movable according to a driving degree of freedom, the sensing mass being elastically coupled to the driving mass so as to be drawn in motion by the driving mass in accordance with the driving degree of freedom and to be movable relative to the driving mass in accordance with the degree of freedom; and

a driving device, coupled to the driving mass to form a microelectromechanical loop including the driving mass and configured to maintain the driving mass in oscillation in accordance to the driving degree of freedom and at a driving frequency.

3. The gyroscope according to claim 2, wherein the driving device is configured to provide the carrier signal and wherein the carrier signal is at the driving frequency.

4. The gyroscope according to claim 3, wherein the base-band signal has a self-test frequency equal to an integer submultiple of the driving frequency.

5. The gyroscope according to claim 4, wherein the self-test actuator comprises a frequency divider coupled to the driving device for receiving the carrier signal and configured to provide the base-band signal.

6. The gyroscope according to claim 4, wherein the sensing device comprises a low-pass filter, cascade coupled to the self-test demodulator and having a cut-off frequency not greater than the self-test frequency.

7. The gyroscope according to claim 1, wherein the capacitive coupling comprises dedicated self-test electrodes, coupled to the self-test actuator for providing a self-test signal.

8. The gyroscope according to claim 1, wherein the capacitive coupling comprises sensing electrodes and selective-connection devices controlled to couple the sensing electrodes selectively to the sensing device and to the self-test actuator in time division.

9. The gyroscope according to claim 8, comprising a plurality of systems of sensing masses, elastically coupled to the body and movable with respect to the body according to respective degrees of freedom, in response to rotations of the body about respective axes;

wherein the self-test actuator is selectively connectable to each system of sensing masses through respective capacitive couplings by the selective-connection devices, to provide the self-test signal;

and wherein the capacitive couplings are configured to apply, in response to the self-test signal, electrostatic forces to move the systems of sensing masses according to the respective degrees of freedom and at the actuation frequency.

10. A self-test method, comprising:

moving a sensing mass of a microelectromechanical gyroscope in accordance with a degree of freedom and at an actuation frequency, the moving including applying electrostatic forces to the sensing mass;

sensing transduction signals indicative of displacements of the sensing mass in accordance with the degree of freedom;

supplying a self-test signal by modulating a carrier signal with a self-test signal; and

discriminating, in the transduction signals, spectral components corresponding to the actuation frequency and spectral components indicative of a movement of the sensing mass in response to rotation of the sensing mass the discriminating including;

generating a first demodulated signal by demodulating the transduction signals using the carrier signal; and

generating a second demodulated signal by demodulating the first demodulated signal using the self-test signal.

11. The method according to claim 10, wherein applying electrostatic forces comprises supplying the self-test signal to the sensing mass through a capacitive coupling.

12. A method, comprising:

driving a sensing mass by introducing a first signal to a microelectromechanical gyroscope, the sensing mass being movably coupled to a body in the microelectromechanical gyroscope, the sensing mass being movable with respect to the body according to a degree of freedom in response to rotations of the body about a first axis;

detecting a second signal corresponding to movement of the sensing mass according to a degree of freedom, the second signal including a first component directed toward movement of the rotations of the body and a second component directed to movement of the sensing mass in response to introduction of the first signal;

producing the first signal by modulating a third signal having a frequency equal to a drive frequency of the sensing mass with a fourth signal having a frequency lower than the drive frequency; and

separating the first and the second component from the second signal, the separating including;

producing a first demodulated signal by demodulating the second signal with a fifth signal having a frequency equal to the drive frequency;

deriving the first component of the second signal from the first demodulated signal;

producing a second demodulated signal by demodulating the first demodulated signal with a sixth signal having a frequency equal to the frequency of the fourth signal; and

deriving the second component of the second signal from the second demodulated signal.

13. The method of claim 12 wherein deriving the second component includes extracting a DC component of the second demodulated signal.

14. The method of claim 12, comprising determining, based on an amplitude of the second component, whether the microelectromechanical gyroscope is functioning correctly.

15. A device, comprising:

a microelectromechanical gyroscope including;

a body;

a driving mass movably coupled to the body; and

a sensing mass movably coupled to the driving mass;

a driving device configured to drive the body, the sensing mass being configured to move in response to movement of the body;

an actuator configured to apply a biasing force to the sensing mass to introduce a corresponding motion to the sensing mass relative to the driving mass;

a sensing device configured to detect motion of the sensing mass according to a degree of freedom and to distinguish in the detected motion a component corresponding to motion of the body from a component corresponding to motion of the sensing mass introduced by the biasing force applied by the actuator, the sensing device including;

a capacitive coupling that couples the sensing device to the body, the sensing device being configured to detect differential changes in the capacitive coupling in response to motion of the sensing mass and configured to produce a corresponding first signal;

first and second demodulators, the first demodulator configured to extract, from a first signal produced by the detected motion of the sensing mass, a second signal corresponding to the motion of the body, and the second demodulator configured to extract, from the second signal, a third signal corresponding to motion of the sensing mass introduced by the biasing force applied by the actuator.

16. The device of claim 15 wherein the actuator is capacitively coupled to the body and the biasing force is produced by electrostatic operation.

17. The device of claim 15 wherein the actuator is configured to apply a modulated self-test signal to the sensing mass as the biasing force.

18. The device of claim 15 wherein:

the sensing mass is one of a plurality of sensing masses, each movably coupled to the driving mass according to a respective axis of freedom;

the actuator is configured to apply a biasing force to each of the plurality of sensing masses to introduce a corresponding motion to each sensing mass according to the respective axis of freedom;

the sensing device is configured to detect motion of each of the sensing masses according to the respective axis of freedom and to distinguish in the detected motion a component corresponding to motion of the body in a corresponding one of a plurality of axes of detection from a component corresponding to motion of the respective sensing mass introduced by the biasing force applied by the actuator.

19. The device of claim 18 wherein:

the actuator is configured to apply the biasing force to each of the plurality of sensing masses sequentially; and

the sensing device is configured to detect motion of each of the sensing masses sequentially.

20. The device of claim 19 wherein each of the sensing masses comprises a respective single capacitive coupling, and wherein the actuator and sensing device are configured to be capacitively coupled to each sensing mass alternately, via the respective single capacitive coupling.

21. The device of claim 15 wherein the device is one of a palm-top computer, a laptop computer, a cell phone, a messaging device, a digital music player, or a digital camera, and wherein the microelectromechanical gyroscope is incorporated in the device to detect movement of the device.