H∞ Loop shaping control for PLL-based mechanical resonance tracking in NEMS resonant mass sensors

A simple dynamic detection of the resonance frequency shift in NEMS resonant mass sensors is described. This is done without the use of an external frequency sweep signal nor a frequency counter limiting the dynamic variation detection. Neither an amplitude control nor a phase switcher is required for maintaining the resonant oscillations. The sensor is driven directly by the VCOpsilas output for which the control signal is calculated by a robust Hinfin controller using loop-shaping method. Only the sensor and the VCOpsilas signals signs are detected and compared so that the controller regulates the phase difference between them, maintaining it at pi/2 which occurs on resonance frequency. The measurement issue is transformed to a novel control problem that rejects the disturbance described by the resonance frequency shift, attenuates the phase noise and guarantees good stability margins.