Resonant Loop Design and Performance Test for a Torsional MEMS Accelerometer with Differential Pickoff

This paper presents an INS (Inertial Navigation System) grade, surface micro-machined differential resonant accelerometer (DRXL) manufactured by an epitaxially grown thick polysilicon process. The proposed DRXL system generates a differential digital output upon an applied acceleration, in which frequency transition is measured due to gap dependent electrical stiffness change. To facilitate the resonance dynamics of the electromechanical system, the micromachined DRXL device is packaged by using the wafer level vacuum sealing process. To test the DRXL performance, a nonlinear self-oscillation loop is designed based on the extended describing function technique. The oscillation loop is implemented using discrete electronic elements including precision charge amplifier and hard feedback nonlinearity. The performance test of the DRXL system shows that the sensitivity of the accelerometer is 24 ㎐/g and its long term bias stability is about 2 ㎎ (1σ) with dynamic range of σ 70g.

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