Generation, Injection and Use of Pilot Tones for Gyro System Characterization

• US 20110192226A1
• Filed: 02/08/2010
• Published: 08/11/2011
• Est. Priority Date: 02/08/2010
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Hayner, David A., Mijuskovic, Dejan
• Granted Patent: US 8,578,775 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719

Abstract

A microcontroller-based method and apparatus are described for generating one or more amplitude and frequency selectable low frequency pilot tone signals (PT) that are injected into an embedded MEMS sensor (110) and mixed signal ASIC (120) and then recovered at the microcontroller (140) to compute or measure various gyro parameters during operational use of the device with no down time or interference with normal operations.

Claims

1. A MEMS sensor, comprising:

a gyro transducer configured to sense an angular rate about a rotational axis, comprising;

a drive mass configured to undergo oscillatory linear motion within a plane;

a sense mass configured to undergo an oscillatory motion out of the plane as a function of the angular rate about the rotational axis within the plane;

one or more electrodes positioned in relation to the sense mass for receiving a rate feedback signal and a quadrature feedback signal which includes a pilot test tone signal, and for electrostatically controlling motion of the sense mass; and

a processor for generating one or more pilot tone signals that are included in the feedback signal, comprising;

a digital pilot tone generation module for generating the one or more pilot tone signals which are injected into the gyro transducer through the one or more electrodes during normal sensing operation of the gyro transducer;

a test signal recovery module for recovering a pilot tone signal from the gyro transducer; and

a gyro parameter extraction module for computing one or more performance parameters of the gyro transducer based on the recovered pilot tone signal without requiring down time or interference with normal sensing operation of the gyro transducer.

2. The MEMS sensor of claim 1, further comprising an integrated circuit coupled between the gyro transducer and the processor which serves as an analog/digital interface between the gyro transducer and the processor.

3. The MEMS sensor of claim 2, where the integrated circuit comprises a synchronous demodulator for generating a demodulated cosine channel which conveys the recovered pilot tone signal, and for generating a demodulated sine channel which conveys an angular rate signal which represents the angular rate about the rotational axis.

4. The MEMS sensor of claim 1, where the gyro transducer and processor are assembled together in a common package.

5. The MEMS sensor of claim 1, where the processor feeds back a quadrature error correction signal to the gyro transducer to correct for quadrature errors by reducing the amplitude of potential interfering signals in the quadrature feedback signal.

6. The MEMS sensor of claim 1, where the gyro parameter extraction module uses the recovered pilot tone signal to estimate sense resonator Q, plant gain, gain offset, one or more bias terms, frequency offsets between the drive and sense resonators, coupling coefficients, delay, or correlation values for the gyro transducer while continuously monitoring the angular rate of the gyro transducer about the rotational axis.

7. The MEMS sensor of claim 1, where the test signal recovery module applies a Goertzel algorithm or another frequency selective filtering method on a pair of baseband output signals received from the gyro transducer to extract or block content from the pair of baseband output signals at one or more predetermined frequencies corresponding to the one or more pilot tone signals which are injected into the gyro transducer.

8. The MEMS sensor of claim 1, where the gyro parameter extraction module computes a predetermined performance parameter by measuring a ratio of a first pilot tone signal that is injected into the gyro transducer to the recovered pilot tone signal corresponding to the first pilot tone signal.

9. The MEMS sensor of claim 1, where the digital pilot tone generation module is configured to generate an amplitude and frequency selectable low frequency pilot tone signal for injection into the gyro transducer.

10. An inertial sensor, comprising:

a transducer unit comprising a feedback input for receiving a feedback control signal, the transducer unit comprising a sense resonator for generating an output signal that is responsive to motion of the transducer unit experiencing an angular velocity;

a synchronous demodulator coupled to receive the output signal from the transducer unit for generating baseband output signals comprising a first baseband output signal for conveying angular velocity data, and a second baseband output signal for conveying oscillation data for the sense resonator which includes a pilot tone signal; and

a transducer feedback control system having a pair of inputs for receiving the first and second baseband output signals, and a feedback output coupled to the feedback input of the transducer unit, the transducer feedback control system comprising;

a pilot test tone signal generator for generating a predetermined pilot tone signal that is applied to the feedback output for injection into the sense resonator;

a filter module for performing frequency selective filtering on the first and second baseband output signals to extract or block predetermined frequency content corresponding to the predetermined pilot tone signal from the quadrature channel, thereby generating an extracted pilot tone signal; and

an extraction module for processing the extracted pilot tone signal to determine one or more predetermined sensor performance parameters for the transducer unit.

11. The inertial sensor of claim 10, where the transducer unit comprises a MEMS gyro sensor for sensing an angular velocity about a rotational axis.

12. The inertial sensor of claim 11, where the MEMS gyro sensor comprises a sense resonator and a drive resonator.

13. The inertial sensor of claim 10, where the synchronous demodulator comprises:

a first analog-to-digital converter for sampling the output signal from the transducer unit at a first oscillating drive signal sin(ω

_Dt) to generate the first baseband output signal for conveying angular velocity data, and

a second analog-to-digital converter for sampling the output signal from the transducer unit at a second oscillating drive signal cos(ω

_Dt) to generate the second baseband output signal for conveying oscillation data for the sense resonator which includes a pilot tone signal.

14. The inertial sensor of claim 10, wherein the first and second baseband output signal are an I signal and a Q signal.

15. The inertial sensor of claim 14, wherein the filter module comprises:

first Goertzel filter for performing the Goertzel algorithm on the I signal; and

second Goertzel filter for performing the Goertzel algorithm on the Q signal.

16. A method of operating an inertial sensor having a transducer with a sense resonator, comprising:

causing an oscillation of the sense resonator in a quadrature channel by injecting a pilot tone signal;

providing a first signal from the sense resonator that is responsive to the oscillation of the sense resonator in the quadrature channel;

providing a second signal from the sense resonator that is responsive to an angular rate experienced by the sense resonator in a non-quadrature channel;

providing a first baseband signal and a second baseband signal responsive to the first and second signals from the sense resonator;

extracting or blocking predetermined frequency content from the first baseband signal and the second baseband signal corresponding to the pilot tone signal, thereby generating an extracted pilot tone signal; and

processing the extracted pilot tone signal to extract one or more inertial sensor performance parameters.

17. The method of claim 16, further comprising using the inertial sensor performance parameters to update one or more control laws or adjust one or more frequency offsets for the inertial sensor.

18. The method of claim 16, where extracting or blocking predetermined frequency content comprises performing a Goertzel algorithm on the first baseband signal and the second baseband signal to extract or block predetermined frequency content corresponding to the pilot tone signal.

19. The method of claim 16, where causing the oscillation of the sense resonator in the quadrature channel comprises generating one or more pilot tone signals PT(nT)=M(nT) sin(ω

_pnT), each having a known amplitude (M), frequency (ω

_P) and time value nT, where n is an integer and T is time value.

20. The method of claim 16, where processing the extracted pilot tone signal comprises measuring amplitude variations in the extracted pilot tone signal and calibrating measured amplitude variations to a Q for the sense resonator.