MEMS inertial sensor with frequency control and method
An inertial sensor has a transducer with a sense resonator. The sense resonator is oscillated. A signal responsive to the oscillation is provided. A first baseband signal and a second baseband signal are provided responsive to the signal responsive to the oscillation of the sense resonator. A signal for controlling a resonance frequency of the sense resonator is provided responsive to performing a Goertzel algorithm on the first baseband signal and the second baseband signal. One use of controlling the resonance frequency is to control an offset between the resonance frequency of the sense resonator and the frequency of the oscillation of drive masses in the sense resonator. Using the Goertzel algorithm is particularly efficient in controlling the resonance frequency.
1. An inertial sensor, comprising:
a drive oscillator;
a transducer unit having a first input coupled to the drive oscillator, an output providing a signal responsive to motion of the transducer unit experiencing an angular velocity, a second input, and a third input, wherein the transducer unit includes a sense resonator;
a frequency tuning unit having an output coupled to the second input of the transducer for altering a resonant frequency of the sense resonator of the transducer, and an input;
a capacitance-to-voltage amplifier having an input coupled to the output of the sense resonator, and an output;
a synchronous demodulator having an input coupled to the output of the capacitance-to-voltage amplifier, and an output providing a pair of baseband signals, wherein one of the pair is representative of the angular velocity;
a transducer feedback control system having a pair of inputs for receiving the pair of baseband signals, and an output coupled to the third input of the transducer unit; and
extraction means for performing a Goertzel algorithm on the pair of baseband signals, multiplying results of performing the Goertzel algorithm, and providing a signal on an output responsive to the results, wherein the output of the extraction means is coupled to the input of the frequency tuning unit.
2. The inertial sensor of claim 1 , further comprising:
a tone generator having an output coupled to the transducer feedback control system.
3. The inertial sensor of claim 2 , wherein the output of the transducer feedback control system includes a pilot frequency.
4. The inertial sensor of claim 3 , wherein the Goertzel algorithm extracts content at the pilot frequency.
5. The inertial sensor of claim 4 , wherein the extraction means further comprises:
control law means for receiving the results and providing an output, wherein the output of the extraction means is responsive to the output of the control law means.
6. The inertial sensor of claim 5 , wherein the extraction means further comprises:
a design offset circuit having an input coupled to the output of the control law means and an output as the output of the extraction means.
7. The inertial sensor of claim 1 , wherein the pair of baseband signals are an I signal and a Q signal.
8. The inertial sensor of claim 7 , wherein the extraction means comprises:
first Goertzel means for performing the Goertzel algorithm on the I signal; and
second Goertzel means for performing the Goertzel algorithm on the Q signal.
9. The inertial sensor of claim 8 , wherein the extraction means further comprises:
multiplier means having a first input coupled to an output of the first Goertzel means and a second input coupled to an output of the second Goertzel means.
10. The inertial sensor of claim 1 , further comprising:
a pilot tone generator for providing a pilot tone at a pilot frequency to the transducer feedback control system, wherein,
the output of the transducer feedback control system includes the pilot frequency.
11. An inertial sensor, comprising:
a transducer that is responsive to motion having an angular rate component, wherein the transducer comprises a sense resonator, wherein the sense resonator comprises a drive resonator;
a capacitance-to-voltage amplifier, coupled to the transducer, having an output for providing a signal responsive to the motion having an angular rate component;
an oscillator, coupled to the transducer, that establishes a frequency of the drive resonator in a first phase;
a pilot tone generator for providing a pilot tone at a pilot frequency;
feedback means coupled to the pilot tone generator and responsive to the signal provided by the capacitance-to-voltage amplifier for providing a correction signal that includes the pilot frequency to the transducer, wherein the sense resonator responds to the pilot tone with an oscillation in a second phase substantially electrically orthogonal to the first phase; and
dynamic frequency control means, responsive to the signal provided by the capacitance-to-voltage amplifier, for providing a signal for use in controlling a resonance frequency of the sense resonator.
12. The inertial sensor of claim 11 , wherein the dynamic frequency control means performs a Goertzel algorithm in providing the signal for controlling the resonance frequency of the sense resonator.
13. The inertial sensor of claim 12 , further comprising:
a demodulator coupled to the capacitance-to-voltage amplifier for generating a first baseband signal and a second baseband signal, wherein the feedback means and the dynamic frequency control means are coupled to the capacitance-to-voltage amplifier through the demodulator.
14. The inertial sensor of claim 13 , wherein the dynamic frequency control means comprises:
Goertzel means for performing the Goertzel algorithm on the first baseband signal to provide a first result and for performing the Goertzel algorithm on the second baseband signal to provide a second result; and
a multiplier for providing an output resulting from multiplying the first result with the second result, wherein
the output of the multiplier is used in generating the signal for controlling the resonance frequency of the sense resonator.
15. The inertial sensor of claim 14 , wherein the dynamic frequency control means further comprises offset means for establishing a desired offset between the resonance frequency of the transducer and the frequency of the sense resonator.
16. A method of operating an inertial sensor having a transducer with a sense resonator, comprising:
causing an oscillation of the sense resonator;
providing a capacitive signal responsive to the oscillation of the sense resonator;
providing a first baseband signal and a second baseband signal responsive to the signal responsive to the oscillation of the sense resonator;
providing a signal for controlling a resonance frequency of the transducer responsive to performing a Goertzel algorithm on the first baseband signal and the second baseband signal.
17. The method of claim 16 , wherein the step of causing an oscillation of the sense resonator is further characterized by the oscillation having:
a first frequency in a first phase for use in determining a motion having an angular rate; and
a second frequency in a second phase substantially electrically orthogonal to the first phase for use in the step of providing a signal for controlling a resonance frequency of the sense resonator.
18. The method of claim 17 , wherein the step of providing a signal for controlling a resonance frequency of the sense resonator is further characterized by the Goertzel algorithm tuned for the first frequency.
19. The method of claim 18 , further comprising:
applying a feedback signal to the transducer, wherein the second frequency is introduced to the sense resonator through the feedback signal.
20. The method of claim 16 , wherein the step of providing a signal for controlling a resonance frequency of the sense resonator is further characterized as being responsive to multiplying results of the performing the Goertzel algorithm on the first baseband signal and the second baseband signal.