Transient Response and Phase-frequency Characteristics of AGC Controlled MEMS Resonant Pressure Sensors

This article presents an automatic gain control (AGC) system with a phase shifter to investigate the nonlinear phase-frequency characteristics resulting from the phase error between the driving force and the speed of the resonant beam in micro-electromechanical systems (MEMS) resonators. Compared to the traditional AGC control loop, this control loop can more accurately solve phase problems encountered during the establishment of the self-excited oscillation process of the resonator. Meanwhile, the transient response of the AGC system and stability of the system are studied in detail, and a quantitative control strategy is proposed to improve the transient characteristics of the resonant sensor and reduce the nonlinear phase-frequency error caused by the detection circuit. By optimizing the control parameters, the settling time of the pressure sensor is less than 200 ms, with no obvious overshoot. The non-linear frequency error caused by the AGC detection circuit is less than 0.2 Hz. Through the static calibration of the resonant pressure sensor (temperature range -40 to 80 ℃, pressure range 2 to 200 kPa), the full range accuracy of the sensor is better than 0.01%FS.