Autonomous Oscillation Control Loop Design for Amplitude Controlled, Frequency Read-Out-Type Resonant Sensors

This paper suggests an autonomous oscillation control loop for frequency read-out-type resonant sensors that produces outputs of variable frequency depending on the input of an external physical quantity. The design goal of the oscillation loop is simultaneously to stabilize the resonance characteristics of the sensor and to automatically track the resonant frequency in order to guarantee highly reliable sensor performance. To this end, the concept of automatic gain control (AGC) is applied so that the loop is designed to maintain the oscillation amplitude as one control objective. The second control objective is to achieve resonance condition tracking even when external influences such as disturbance and noise exist. For the verification of the proposed control loop design, an example resonant sensor system is modeled, and a control loop and controller that accompany the system are also designed. Finally, the proposed loop performance was demonstrated via simulations which consider practical noise elements. The theoretical results were further verified via sensor's transient responses and noise analysis.