Resonance frequency control and digital correction for capacitive MEMS gyroscopes within electromechanical bandpass delta-sigma-modulators

Abstract

This paper reports on a resonance frequency control for vibratory MEMS gyroscopes. The angular rate readout system is based on a continuous-time electromechanical bandpass Delta-Sigma Modulator (emDSM). Due to mismatch of the mechanical resonance frequencies of the gyroscope the in-band noise (IBN) of the readout system is increased. The presented frequency control concept consists of a digital resonance frequency detection based on injected testsignals and a frequency control which controls the resonance frequency of the gyroscope's detection mass to achieve matched mode condition. The frequency control voltages make use of the spring softening effect. Due to the applied voltages also the feedback force is affected. This causes modulation effects. A novel digital correction will be presented which is able to compensate the modulation effect and decreases the IBN by up to 40 dB.