Switched Capacitor Micro-accelerometer Capacitance Detection Circuit's Design And Research

Capacitive micro-accelerometer is a hot topic in the field of MEMS. An important problem to be solved in the readout circuits is the detection of the capacitance changes in the acceleration sensor. It has practical significance to research the front-end detection circuits, which are easy to be integrated, and applied to the readout circuit of the capacitive micro-accelerometer sensors.In this thesis, a type of switched-capacitor(SC) front-end detection circuit is designed for the capacitive accelerometer readout circuit. The correlated double sampling (CDS) technique is used in the SC front-end gain circuit, to reduce the influence of the finite gain, the input DC offset voltage and the low frequency noise of the operational amplifier (op-amp). Noise, common and differential response characteristics of the SC front-end detection circuit are analyzed. The fully differential gain-boosted op-amp is used to meet the requirement of the gain-accuracy of the front-end circuit. The noise and frequency response characteristics of the op-amp are discussed. To reduce the power consumption and improve the system stability, switched-capacitor common mode feedback circuit is applied to the op-amp.The whole SC front-end detection circuit and the gain-boosted op-amp applied to the former are designed and simulated in 0.35-μm CMOS process. The simulation results show that the op-amp has about 126.2dB open loop DC gain, 60.68M unity gain bandwidth, and phase margin of 76.7°; the SC detection circuit has 4Vpp output swing, while consuming only 4.15mW with a 5V supply.