An integrated CMOS micromechanical resonator high-Q oscillator

A completely monolithic high-Q oscillator, fabricated via a combined CMOS p lus surface micromachining technology, is described, for which the oscillat ion frequency is controlled by a polysilicon micromechanical resonator with the intent of achieving high stability. The operation and performance of m icromechanical resonators are modeled, with emphasis on circuit and noise m odeling of multiport resonators, A series resonant oscillator design is dis cussed that utilizes a unique, gain-controllable transresistance sustaining amplifier. We show that in the absence of an automatic level control loop, the closed-loop, steady-state oscillation amplitude of this oscillator dep ends strongly upon the de-bias voltage applied to the capacitively driven a nd sensed mu resonator, Although the high-Q of the micromechanical resonato r does contribute to improved oscillator stability, its limited power-handl ing ability outweighs the Q benefits and prevents this oscillator from achi eving the high short-term stability normally expected of high-Q oscillators .