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 method of tuning a device having a mechanical resonator, the method comprising:
producing an output signal of the mechanical resonator;
shifting a phase of the output signal of the mechanical resonator to produce a phase-shifted signal having a different phase than the phase of the output signal of the mechanical resonator, wherein shifting the phase of the output signal of the mechanical resonator comprises performing a coarse phase adjustment with a variable coarse phase adjustor and a fine phase adjustment with a variable fine phase adjustor; and
providing the phase-shifted signal to the mechanical resonator.
2 . The method of claim 1 , wherein shifting the phase of the output signal of the mechanical resonator comprises inverting the output signal of the mechanical resonator.
3 . The method of claim 1 , wherein performing the coarse phase adjustment comprises inverting the output signal of the mechanical resonator.
4 . The method of claim 1 , wherein the coarse phase adjustment is performed prior to the fine phase adjustment.
5 . The method of claim 4 , wherein performing the coarse phase adjustment comprises inverting the output signal of the mechanical resonator.
6 . The method of claim 1 , wherein the fine phase adjustment is performed prior to the coarse phase adjustment.
7 . The method of claim 1 , further comprising amplifying the output signal of the mechanical resonator prior to shifting the phase of the output signal of the mechanical resonator.
8 . The method of claim 1 , further comprising amplifying the phase-shifted signal.
9 . The method of claim 1 , wherein the mechanical resonator has a resonance frequency that varies with temperature, and wherein shifting the phase of the output signal of the mechanical resonator comprises shifting the phase to compensate for a temperature-induced shift in the resonance frequency of the mechanical resonator.
10 . The method of claim 1 , wherein the mechanical resonator has a variable resonance frequency, and wherein shifting the phase of the output signal of the mechanical resonator comprises shifting the phase to compensate for variations in the resonance frequency of the mechanical resonator.
11 . The method of claim 10 , wherein the variable resonance frequency varies in response to variations in ambient pressure.
12 . The method of claim 10 , wherein the mechanical resonator is contained at least partially within a package, and wherein the variable resonance frequency varies in response to variations in package-induced stress.
13 . The method of claim 10 , wherein the mechanical resonator is formed of two or more materials, and wherein the variable resonance frequency varies in response to material-dependent stress.
14 . The method of claim 1 , further comprising performing stress tuning of the device using electrostatic or piezoelectric techniques.
15 . The method of claim 1 , wherein the output signal comprises multiple ends having approximately equal phases.
16 . The method of claim 15 , wherein shifting the phase of the output signal comprises shifting the phases of the ends of the output signal by an approximately equal amount.
17 . The method of claim 15 , wherein shifting the phase of the output signal comprises shifting a phase of a first end of the output signal by a first amount and shifting a phase of a second end of the output signal by a second amount different than the first amount.
18 . The method of claim 17 , wherein the first amount and the second amount differ by between approximately 1-10 degrees.
19 . A device, comprising:
a mechanical resonator; and
a phase shifter, wherein the phase shifter comprises a variable coarse phase adjustment subcircuit and a variable fine phase adjustment subcircuit, and
wherein the mechanical resonator and the phase shifter are configured in a feedback loop.
20 . The device of claim 19 , wherein the mechanical resonator is at least part of a microelectromechanical system (MEMS).
21 . The device of claim 19 , wherein the mechanical resonator is a suspended mechanical resonator configured to support Lamb waves, the mechanical resonator comprising:
a layer comprising a piezoelectric material; and
multiple electrodes formed on the layer.
22 . The device of claim 21 , wherein the piezoelectric material comprises aluminum nitride.
23 . A method of tuning a mechanical resonator of an oscillating circuit, the method comprising:
producing an output signal of the mechanical resonator comprising a first end and a second end;
amplifying and phase shifting the first end and second end by different amounts to produce a modified signal; and
inputting the modified signal to the mechanical resonator.
24 . The method of claim 23 , wherein amplifying the first end and second end by different amounts comprises amplifying only one of the first end and the second end.
25 . The method of claim 23 , wherein phase shifting the first end and second end by different amounts comprises phase shifting only one of the first end and the second end.