Methods and apparatus for tuning devices having mechanical resonators
Methods and apparatus for tuning devices having mechanical resonators are described. In one implementation, a mechanical resonator and a phase shifter are configured in a feedback loop, so that the phase shifter shifts the phase of the resonator output signal. The amount of phase shift induced by the phase shifter may be variable. In another implementation, an LC tuning subcircuit is coupled to a mechanical resonator. In some implementations, the LC tuning subcircuit has a variable capacitance. One or more of the apparatus described herein may be implemented as part, or all, of a microelectromechanical system (MEMS).
1. A device, comprising:
a mechanical resonator having a series resonance frequency, the mechanical resonator comprising:
a layer comprising a piezoelectric material and having a thickness less than three wavelengths of the series resonance frequency; and
multiple electrodes formed on the layer,
wherein the mechanical resonator is configured to support Lamb waves, and
a drive circuit coupled to the mechanical resonator and configured to produce a drive signal for driving the mechanical resonator; and
a tuner coupled to the mechanical resonator and configured to be able to adjust an operating frequency of the device to frequencies less than and greater than the series resonance frequency,
wherein the tuner comprises an LC tuning subcircuit comprising a variable inductor and a variable capacitor,
wherein the mechanical resonator, variable inductor, and variable capacitor are connected in series,
wherein the tuner is configured to adjust the operating frequency of the device over a range of at least 400 parts per million of the series resonance frequency, and
wherein an output of the drive circuit is connected to an input of the variable capacitor, an output of the variable capacitor is connected to an input of the variable inductor, an output of the variable inductor is connected to an input of the mechanical resonator, and an output of the mechanical resonator is connected to an input of the drive circuit.
2. The device of claim 1 , wherein the tuner is configured to adjust the operating frequency of the device over a range of at least 500 parts per million of the series resonance frequency.
3. The device of claim 2 , wherein the tuner is configured to adjust the operating frequency of the device over a range of between 500 parts per million and 700 parts per million of the series resonance frequency.
4. The device of claim 3 , wherein the tuner is configured to adjust the operating frequency of the device over a range of between 600 parts per million and 800 parts per million of the series resonance frequency.
5. The device of claim 1 , wherein the piezoelectric material is aluminum nitride.
6. The device of claim 1 , wherein the operating frequency of the device is between 100 MHz and 1 GHz.