A capacitive readout circuit with DC sensing method for micromachined gyroscopes

In this work, a capacitive readout circuit for micromachined capacitive gyroscope is presented. Compared with the commonly used AC sensing which need a high frequency carrier to modulate the signal into high frequencies, the DC sensing only need a high DC voltage applied on the proof mass of the gyroscope, therefore simplify the circuit structure. In addition, the proposed circuit can partially suppress the mechanical coupling from the drive mode to the sense mode of the gyroscope, automatically cancel the DC offset due to capacitance mismatch, lower the input referred noise by two optimized stages of amplifier, and maximize the circuit signal-to-noise (SNR). The circuit is designed and fabricated by Charter 0.35 um mixed-signal CMOS process, and the chip size is 1.2 mm×1.2 mm. The circuit was successfully used to test a tuning fork gyroscope, and a 10 dB reduction of the mechanical coupling has been demonstrated.