H∞ loop-shaping control of a PLL-based oscillation loop for dynamic resonance tracking in NEMS mass sensors arrays

A robust control scheme for dynamic resonance frequency tracking in NEMS resonant mass sensors arrays is described. This is accomplished using a simple measurement set-up that can be integrated to the sensor altering the frequency resolution and enhancing the performance and the robustness to the parameters dispersion effect and to the global model uncertainty. It is based on a PLL oscillating loop in which the VCO generates the common excitation of the whole array and the feedback signal is given by the collected array´s output. The measurement issue is turned to a servo-control problem that maintains the phase shift between the drive signal and the output´s one at - π/2 that occurs on resonance, adjusting the VCO frequency to the sensor´s variant resonance frequency. The controller is designed using H∞ loop-shaping method, rejects the disturbance described by the resonance frequency shift with a large bandwidth, attenuates the phase noise and guarantees good stability margins. The VCO control voltage shows an image of the amount of change in the resonance frequency surpassing the need of additional hardware components and external measurement circuitries.