Research On Sigma-Delta Micro-machined Capacitive Accelerometer System

Micro-accelerometers are one of the important research areas in MEMS, with the widely application in the areas such as industrial control, environmental monitoring, automotive systems and biomedical diagnostics. The micro-machined capacitive accelerometer is a typical MEMS product. The research based on its modeling, simulation and optimization is very important for the performance improving, shortening the development period and lowering the cost.The development of capacitive micro-accelerometer, the principle of micro-machined, the closed-loop micro-accelerometer and sigma-delta technology is analyzed in this thesis. On the basis of the above theories, an equivalent system for micro-machined capacitive acceleromenter is created. A Second-order sigma-delta modulator is used for ADC in this system. Micro-accelerometer system is fulfilled in closed-loop operating mode due to feedback signal provided by modulator. The non-ideal cases of the sensor system are carefully analyzed in the study. In order to meet simulation in non-ideal, the non-idealities model and the whole system model of sigma-delta capacitive accelerometer are constructed in SIMULINK environment. The SNR of the system model can obtain 76dB and resolution results in 12bit considering above non-idealities.A second-order modulator circuit is designed in the paper. The design principle and idea of the key circuit blocks are especially introduced. The operational amplifier, switch-capacitor circuits, comparator and the clock generator have been designed based on 0.35um CMOS standard process. The correctness of the module is verified with the HSPICE circuit-level simulation.The result shows that the system model and modulator circuit designed in this paper can satisfy the design demands of micro-g resolution accelerometer.