CMOS interfacing and signal conditioning circuit for MEMS gyroscope

The basic principle of MEMS gyroscope depends on the detection of coriolis signal when a vibrating object is subjected to rotation. The interface and the conditioning circuit for MEMS gyroscope include primary excitation circuit and sensing circuit. The primary excitation (drive loop) is a closed loop feedback circuit in which the drive electrodes are subjected to an ac excitation and the ac signal is sensed from the other side of the drive electrodes and the resultant frequency sensed from the drive electrodes is matched with the resonant frequency of the proof mass of the gyroscope so that maximum amplitude of the signal is obtained. The closed loop control circuit for primary excitation phase (drive loop) of gyroscope typically consists of a trans-impedance amplifier (TIA), low pass filter (LPF), variable gain amplifier (VGA) and proportional Integral controller (PI) and driving buffer. In the sensing phase (sense loop), the MEMS gyroscope is subjected to rotation by an angle and the rate of rotation is sensed at the sense electrodes. The sensing circuit (sense loop) consists of a trans-impedance amplifier, synchronous demodulator(gilbert cell mixer) and a low pass filter (LPF). The specification requirements of the trans-impedance amplifier in sensing circuit (sense loop) are critical as compared to the primary excitation circuit (drive loop). In this paper, interfacing and signal conditioning circuits for the implementation of primary excitation circuit and sense circuit have been explored. After comparison of various literature survey, a particular architecture is being chosen and thorough analysis is carried out, based on which the specification requirements of each block has been derived. The design and simulation has been carried out in UMC 0.35um technology.