Abstract
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 (VP) 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-&null CMOS-MEMS platform with typical open-loop resonator Q-factor of 1500. The best-case close-to-carrier phase noise is obtained from a 1.23-MHz 180-&null integrator-differentiator transimpedance amplifier-based nonlinear oscillator with VP = 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 = 189.3 dB at 10-Hz offset).