A universal interface circuit for capacitive vibratory microgyroscopes

In widely used closed-loop drive scheme for capacitive vibratory microgyroscopes, additional capacitive interfaces for monitoring of the drive mode is avoidless. In addition, capacitive interfaces for tuning the resonance frequency of microgyroscopes is also necessary for closed-loop detection. Introducing these additional capacitive interfaces, the sense capacitances became much smaller, and the efficiency of the driving became lower. Correspondingly the sensitivity of the capacitive vibratory microgyroscopes decayed. This paper presents a universal and simple interface circuit without these additional capacitive interfaces. One single-ended bridge is formed by a pair of drive capacitors and sense capacitors. The vibrating mass, as the output of the bridge, is held at virtual ground by a charge integrator. Drive voltage combined with high-frequency carriers is applied to fixed node of the drive capacitors. High-frequency carriers with offset which are used as feedback force are applied to fixed node of the sense capacitors. Thus output of the integrator includes modulated driving, sensing mode signals and the drive voltage. Due to the high Q of the microgyroscopes, the carriers have no impact on the drive mode. And the frequency of the drive voltage is usually much lower than the carriers, so a low pass filter can be used to eliminate the influence of the drive voltage on the integrator. The two carriers have different frequencies, and the band pass filters can be used to separate the modulated driving and sensing mode signals. Using two capacitive vibratory microgyroscopes with different structures and capacitive interfaces, the experiments were respectively carried out. The results indicated that the 1/f noise was effectively reduced, (and) the couplings of the driving ()on sensing signal was eliminated. The circuit can resolve variations of input capacitance less than 1 fF.