Dual Mode Gyroscope

• US 20170074656A1
• Filed: 09/14/2015
• Published: 03/16/2017
• Est. Priority Date: 09/14/2015
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: Tallur, Siddharth, Bhave, Sunil Ashok
• Granted Patent: US 10,234,288 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5677 of essentially two-dimensional vibrators, e.g. ring-shaped vibrators
• CPC Class Codes: G01C 19/5684 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5698 using acoustic waves, e.g. surface acoustic wave gyros

Abstract

A BAW gyroscope is configured to operate with two pairs of orthogonal modes instead of a single pair in order to mitigate the impact of changes in gaps (e.g., introduced from external stresses such as thermal gradients, external shocks, mechanical stress/torque, etc.). Specifically, the BAW gyroscope resonator is configured to be simultaneously driven to resonate with a two disparate resonant modes (referred to herein as the “fundamental” mode and the “compound” mode), with the same set of drive electrodes used to drive both resonant modes (i.e., all of the drive electrodes are used to drive the two drive modes). When the sensor experiences external rotation, energy couples from the driven modes of vibration to two corresponding orthogonal sense modes via the Coriolis force. The same set of sense electrodes is used to sense both sense modes (i.e., all of the sense electrodes are used to sense the two sense modes). The fundamental mode is differential with respect to the electrodes, while the compound mode is seen as common-mode with respect to the electrodes. Thus, differential gap change will impact offset of rate measured with the fundamental mode only, while common-mode gap change will impact offset of rate measured with the compound mode only.

Claims

1. A bulk acoustic wave gyroscope comprising:

a resonator;

a set of drive electrodes including at least one pair of opposed drive electrodes;

a set of sense electrodes including at least one pair of opposed sense electrodes; and

a gyroscope control circuit configured to provide drive signals to the set of drive electrodes to drive the resonator to resonate with two disparate drive modes including a fundamental mode and a compound mode, receive sense signals from the set of sense electrodes to sense two orthogonal sense modes of the resonator including a sensed fundamental mode and a sensed compound mode, and produce a gyroscope rate output signal based on a weighted sum of the sensed fundamental and compound modes.

2. A gyroscope according to claim 1, wherein all of the drive electrodes are used to drive both the fundamental mode and the compound mode, and wherein all of the sense electrodes are used to sense both of the sensed modes.

3. A gyroscope according to claim 1, wherein the resonator is a ring-shaped resonator.

4. A gyroscope according to claim 1, wherein the drive electrodes are arranged to drive the drive modes along at least one drive axis, and wherein the sense electrodes are arranged to sense the sense modes along at least one sense axis that is 45 degrees offset from the at least one drive axis.

5. A gyroscope according to claim 1, wherein the fundamental mode frequency and the compound mode frequency are different.

6. A gyroscope according to claim 1, wherein the fundamental mode frequency and the compound mode frequency are the same.

7. A gyroscope according to claim 1, wherein the fundamental mode and the compound mode are N=2 modes.

8. A gyroscope according to claim 1, wherein the fundamental mode and the compound mode are N=3 modes.

9. A gyroscope according to claim 1, wherein the gyroscope control circuit comprises:

a fundamental mode driver configured to apply a differential signal across opposing drive electrodes at a fundamental mode frequency;

a compound mode driver configured to apply a same polarity signal to opposing drive electrodes at a compound mode frequency;

a fundamental mode sense circuit configured to demodulate sensed fundamental mode signals at the fundamental mode frequency;

a compound mode sense circuit configured to demodulate sensed compound mode signals at the compound mode frequency; and

a rate output circuit configured to produce the gyroscope rate output signal based on a weighted sum of the demodulated signals.

10. A gyroscope according to claim 9, wherein the fundamental mode driver comprises a first output coupled to a first subset of the drive electrodes and a second output coupled to a second subset of the drive electrodes, and wherein the compound mode driver comprises an output coupled to all of the drive electrodes.

11. A gyroscope according to claim 9, wherein the fundamental mode sense circuit comprises a differential trans-impedance amplifier having a first input coupled to a first subset of the sense electrodes and a second input coupled to a second subset of the sense electrodes and further comprises a demodulator coupled to receive an output of the differential trans-impedance amplifier, and wherein the compound mode sense circuit comprises a single-ended amplifier having an input coupled to the sense electrodes and a demodulator coupled to receive an output of the single-ended amplifier.

12. A method for operating a bulk acoustic wave gyroscope having a resonator, a set of drive electrodes including at least one pair of opposed drive electrodes, and a set of sense electrodes including at least one pair of opposed sense electrodes, the method comprising:

providing drive signals to the set of drive electrodes to drive the resonator to resonate with two disparate drive modes including a fundamental mode and a compound mode;

receiving sense signals from the set of sense electrodes and sensing from the received sense signals two orthogonal sense modes of the resonator including a sensed fundamental mode and a sensed compound mode; and

producing a gyroscope rate output signal based on a weighted sum of the sensed fundamental and compound modes.

13. A method according to claim 12, wherein:

providing the drive signals comprises applying a differential signal across opposing drive electrodes at a fundamental mode frequency and applying a same polarity signal to opposing drive electrodes at a compound mode frequency;

sensing the two orthogonal sense modes comprises demodulating sensed fundamental mode signals at the fundamental mode frequency and demodulating sensed compound mode signals at the compound mode frequency; and

producing the gyroscope rate output signal comprises producing the gyroscope rate output signal based on a weighted sum of the demodulated signals.

14. A method according to claim 12, wherein the fundamental mode frequency and the compound mode frequency are different.

15. A method according to claim 12, wherein the fundamental mode frequency and the compound mode frequency are the same.

16. A gyroscope control circuit for a dual-mode BAW gyroscope, the gyroscope control circuit comprising:

a fundamental mode driver configured to apply a differential signal across opposing drive electrodes of a set of drive electrodes at a fundamental mode frequency;

a compound mode driver configured to apply a same polarity signal to opposing drive electrodes of the set of electrodes at a compound mode frequency;

a fundamental mode sense circuit configured to demodulate sensed fundamental mode signals from opposing sense electrodes of a set of sense electrodes at the fundamental mode frequency;

a compound mode sense circuit configured to demodulate sensed compound mode signals from opposing sense electrodes of the set of sense electrodes at the compound mode frequency; and

a rate output circuit configured to produce a gyroscope rate output signal based on a weighted sum of the demodulated signals.

17. A gyroscope control circuit according to claim 16, wherein the fundamental mode driver comprises a first output coupled to a first subset of the drive electrodes and a second output coupled to a second subset of the drive electrodes, and wherein the compound mode driver comprises an output coupled to all of the drive electrodes.

18. A gyroscope control circuit according to claim 16, wherein the fundamental mode sense circuit comprises a differential trans-impedance amplifier having a first input coupled to a first subset of the sense electrodes and a second input coupled to a second subset of the sense electrodes and further comprises a demodulator coupled to receive an output of the differential trans-impedance amplifier, and wherein the compound mode sense circuit comprises a single-ended amplifier having an input coupled to the sense electrodes and a demodulator coupled to receive an output of the single-ended amplifier.

19. A gyroscope control circuit according to claim 16, wherein the fundamental mode frequency and the compound mode frequency are different.

20. A gyroscope control circuit according to claim 16, wherein the fundamental mode frequency and the compound mode frequency are the same.