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Two methods for limiting the oscillation amplitude in micromechanical resonators, typically used in many kinds of MEMS sensors, are discussed and compared. First, it is shown how the presence of parasitic capacitances sets several constraints on the design of the oscillating circuit gain and bandwidth. The paper specifically focuses on the case of a transimpedance based oscillator coupled to a clamped-clamped beam, that forms the sensing element of a resonant accelerometer. Experimental results then show that the oscillating amplitude can be limited either using an electronic limiting stage, or exploiting the mechanical nonlinearities of the beam for large displacements. Though the latter approach is advantageous in terms of power dissipation, it is shown that the sensitivity of the resonant accelerometer is strongly compromised.
Date of Publication: June 2012