A Study on the Design Parameters for MEMS Oscillators Incorporating Nonlinearities

This paper presents a comprehensive study on the design parameters for MEMS oscillators incorporating nonlinear mechanisms. Three different CMOS amplifier topologies in tandem with double-ended tuning-fork resonators are developed to perform a general study, thus revealing the CMOS circuit design scenarios for low phase noise. The close-to-carrier phase noise cancellation is experimentally demonstrated by either varying the gain and phase of the feedback amplifier or the dc-bias (V-p) of the resonator for harnessing the optimal bias point at the resonator's lower bifurcation point. All prototype oscillators in this paper are fabricated by a monolithic 0.35-mu m CMOS-MEMS platform with typical openloop resonator Q-factor of 1500. The hest-case close-to-carrier phase noise is obtained from a 1.23-MHz 180-mu W integratordifferentiator transimpedance amplifier-based nonlinear oscillator with V-p = 70 V, exhibiting phase noise of -80 dBc/Hz at 10 Hz, -97 dBc/Hz at 100-Hz, and -112 dBc/Hz at 1-kHz offset (FOM = 1893 dB at 10-Hz offset).