| In the past two decades, MEMS has developed rapidly. As the development of MEMS, gyroscope has been progressing steadily. The size of gyroscope is small, usually in micrometers, and the output signal of the gyroscope is small. The variation of capacitance in gyroscope is very small too, so there is a high demand of the sensitivity, resolution and linear range in readout circuit. For majority of the gyro used bulk silicon micromachining, the system noise is mainly from the readout circuit, so the use of high-precision capacitive sensing circuit scheme to achieve small electric charge read out is very important. This paper presents a number of programs to achieve this readout circuit, and then do some theoretical analysis and simulation.A differential detection of continuous-time readout circuit is used in this paper. This circuit is anti-interference, and easy to implement. The main noise of the circuit comes from the thermal noise and flicker noise. Optimized the ratio of width to length by capacitance matching to achieve the most optimal design. The input referred noise of pre-amplifier is 10.1nV/√Hz, open-loop gain is 96dB, the phase margin is 60°, and PSRR is 98dB, the relevant performance can meet the requirements of low noise readout circuit. Optimized for low noise to the other part of the readout circuit, and proposed some means including reducing the parasitic capacitance, suppressing external noise, useing SIGMA-DELTA modulator, and some other low-noise design methods.Simulation results show that the overall noise of the readout circuit is 51.156nV/√Hz, compared to the original laboratory readout circuit, the noise is greatly reduced. Finally, designed the ASIC readout circuit layout, which is based on 18V0.5μm COMS double-well process. The overall area of the layout is 4499μm×1940μm. The simitation shows that the noise of op-amp is 16.5nV/√Hz, and the noise of overall circuit is 59.691nV/√Hz, can meet the requirements of the low-noise readout circuit. |
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