Two-mass MEMS velocity sensor feedback control loop design

This paper presents theoretical and experimental results about the design of an internal velocity feedback loop in a new capacitive micro-electro-mechanical system (MEMS) velocity sensor. The sensor comprises two mass-spring systems connected in series, termed the principal and control sensors. The control sensor output is fed to an electrostatic actuator that acts between the sensor´s frame and the principal proof mass. The aim of the internal feedback control loop is to generate a sky-hook damping effect on the principal sensor, so that, in the frequency band of interest, the output of the sensor is proportional to the base velocity. The sensor is fabricated on a Silicon-on-Isolator (SOI) wafer. The sensor interface and the controller are implemented on a printed circuit board (PCB). The design of the control loop is carried out offline; using measured frequency response functions (FRFs) between the displacements of the two proof masses with respect to i) the base acceleration, measured with a reference accelerometer mounted on the sensor´s frame, and ii) the voltage signal driving the electrostatic actuator for the velocity feedback loop.