Noise reduction in mems oscillators and related apparatus and methods

Abstract

Mechanical resonating structures are used to generate signals having a target frequency with low noise. The mechanical resonating structures may generate output signals containing multiple frequencies which may be suitably combined with one or more additional signals to generate the target frequency with low noise. The mechanical resonating structures may be used to form oscillators.

What is claimed is: 
     
         1 . A method, comprising:
 generating a multiple-frequency output signal of a piezoelectric mechanical resonating structure;   generating, from the multiple-frequency output signal, a correction signal comprising at least one frequency; and   combining the correction signal and at least a portion of the multiple-frequency output signal.   
     
     
         2 . The method of  claim 1 , wherein generating the multiple-frequency output signal comprises generating a first frequency comb, and wherein generating the correction signal comprises generating a second frequency comb. 
     
     
         3 . The method of  claim 2 , wherein the mechanical resonating structure is configured to exhibit multiple resonance modes, and wherein generating the first frequency comb comprises exciting the multiple resonance modes of the mechanical resonating structure. 
     
     
         4 . The method of  claim 2 , wherein generating the first frequency comb comprises nonlinearly exciting the mechanical resonating structure. 
     
     
         5 . The method of  claim 2 , wherein generating the second frequency comb comprises mixing the multiple-frequency output signal. 
     
     
         6 . The method of  claim 1 , wherein combining the correction signal and at least a portion of the multiple-frequency output signal comprises performing a subtraction operation. 
     
     
         7 . The method of  claim 1 , wherein generating the correction signal comprises processing first and second frequencies of the multiple-frequency output signal. 
     
     
         8 . The method of  claim 1 , wherein combining the correction signal and at least the portion of the multiple-frequency output signal produces a combined signal comprising a target frequency, and wherein the combined signal comprising the target frequency has greater stability than the multiple-frequency output signal. 
     
     
         9 . The method of  claim 1 , wherein combining the correction signal and at least the portion of the multiple-frequency output signal produces a combined signal comprising a target frequency, and wherein the combined signal comprising the target frequency has improved noise characteristics compared to the multiple-frequency output signal. 
     
     
         10 . A timing oscillator, comprising:
 a piezoelectric mechanical resonator;   a driving circuit configured to excite the mechanical resonator, wherein the mechanical resonator is configured to produce a multiple-frequency output signal in response to being excited by the driving circuit;   correction circuitry configured to generate, from the multiple-frequency output signal, a correction signal comprising at least one frequency; and   combination circuitry configured to combine the correction signal and at least a portion of the multiple-frequency output signal.   
     
     
         11 . The timing oscillator of  claim 10 , wherein the multiple-frequency output signal comprises a first frequency comb, and wherein the correction signal comprises a second frequency comb. 
     
     
         12 . The timing oscillator of  claim 11 , wherein the mechanical resonator is configured to exhibit multiple resonance modes, and wherein the driving circuit is configured to excite the multiple resonance modes of the mechanical resonator. 
     
     
         13 . The timing oscillator of  claim 12 , wherein the multiple resonance modes include a target resonance mode and at least one spurious resonance mode, and wherein the at least one spurious resonance mode is associated with a coupling between a suspended portion of the mechanical resonator and at least one anchor. 
     
     
         14 . The timing oscillator of  claim 11 , wherein the driving circuit is configured to nonlinearly excite the mechanical resonator. 
     
     
         15 . The timing oscillator of  claim 11 , wherein the timing oscillator comprises mixing circuitry, wherein the mixing circuitry includes the correction circuitry and the combination circuitry, and wherein the mixing circuitry is configured to generate the second frequency comb at least in part by mixing the multiple-frequency output signal. 
     
     
         16 . The timing oscillator of  claim 10 , wherein the correction circuitry is configured to generate the correction signal by processing at least two separate frequencies of the multiple-frequency output signal. 
     
     
         17 . The timing oscillator of  claim 10 , wherein the combination circuitry comprises circuitry configured to perform a subtraction operation to produce a combined signal. 
     
     
         18 . The timing oscillator of  claim 17 , wherein the combined signal comprises a target frequency, and wherein the combined signal comprising the target frequency has greater stability than the multiple-frequency output signal. 
     
     
         19 . The timing oscillator of  claim 17 , wherein the combined signal comprises a target frequency, and wherein the combined signal comprising the target frequency has improved noise characteristics compared to the multiple-frequency output signal. 
     
     
         20 . The timing oscillator of  claim 10 , wherein the mechanical resonator comprises silicon.