Compensation methods for a silicon tuning fork gyroscope

The paper presents compensation methods for a robust gyroscope sensor with an electrical and mechanical self-test option and the ability to suppress the quadrature error. The presented sensor is based on a tuning-fork working principle. The mechanical part is assembled in bulk-technology produced with a wet etching process. The two detection elements are manufactured with a standard CMOS-process and the material of the two thin-film actuators is aluminium nitride (AlN). The two actuators can be controlled independently from each other. Two electronic PCB's were made for actuating and measurement. One is including the analogue signal path; the second PCB is the digital electronics consisting of a FPGA and other peripherals. The tuning fork is actuated in a primary oscillation mode also called drive mode. For keeping the oscillation in resonance, a digital PLL is used in a forced feedback loop. To provide a constant energy in the drive mode an amplitude gain control is implemented. An appearing angular rate causes the Coriolis force which is actuating secondary oscillation, also called detection mode. The amplitude of this oscillation is proportional to the angular rate. The signal has a disturbing component mainly resulting from the mechanical imbalance. To separate these two signal parts from each other a synchronous demodulator followed by a digital filter chain has been developed. To achieve a suppression of the mechanical imbalance signal a control-loop is used to shift the phases of the two actuation signals. This creates an additional force that compensates the disturbing influences of the mechanical imbalance. The electrical imbalance as well as some other signal sources are compensated by stimulating the mechanical system with different amplitudes for the left and the right actuator. With the implementation of these compensation methods the performance of the sensor is increasing. An enhanced temperature stability over operation was achieved with the means of this compensation.