| Micromachined gyroscopes, which can be used to sense angular velocity, have a variety of applications in the area of automobile, inertial navigation and commercial electronics due to their small size, high reliability and low cost. The weak signal from gyroscopes and other sensors should be detected by methods for weak signal detection. The quality of signal detection directly influences the precision of sensors. It is of great importance to design a better detecting circuit with high sensitivity and strong interference immunity for the sensors. Firstly, the source and properties of the noise are analyzed. We can amplify the weak signal, reject noise and enhance signal-to-noise ratio (SNR) according to the periodicity and the correlation of signal and the randomicity of noise. The model of noise analysis and the measures of anti-jamming for amplifiers are also presented.Secondly, several detecting methods are introduced, including correlation detection,synchronous integrator, lock-in amplifier, sigma-delta analog to digital conversion. Their performances are analyzed by theoretical calculations.Thirdly, based on the matched filter characteristics of synchronous integrator, a lock-in amplifier with both correlation detection and synchronous integrator is designed, and then the anti-noise performance of the system is enhanced. The control of the MCU——MSC1210 makes the system more flexible and can be used for different sensors.At last, the foregoing circuit is implemented in form of four-layer PCB and the components with ultra low-noise are selected. Then the performance of the system is tested and the results are consistent with theoretical calculations. It is proven that the system has strong noise immunity by the experimental results. The full scale sensitivity can reach 100nV, which approaches the medium performance of lock-in amplifier equipment.Based on the experiment of this thesis, we can improve its performance and design special detecting circuit with small size for the sensors.
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