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 a differential output signal of the mechanical resonator, the differential output signal comprising a first end and a second end;
producing a phase-shifted signal by phase shifting at least one of the first end and the second end, wherein producing the phase-shifted signal comprises phase shifting the first end by a first amount and phase shifting the second end by a second amount, wherein the first amount and the second amount differ from each other by between three degrees and twenty degrees; and
providing the phase-shifted signal as an input signal to the mechanical resonator.
2. The method of claim 1 , wherein the first amount and the second amount are variable.
3. The method of claim 1 , wherein the first amount is within 5 degrees of the second amount.
4. The method of claim 1 , wherein phase shifting the first end of the differential output signal by a first amount and phase shifting the second end of the differential output signal by a second amount is performed to maintain a constant power of the phase-shifted signal over time.
5. The method of claim 1 ,
wherein producing the phase-shifted signal further comprises amplifying the first end and second end by different amounts.