The design of micro-capacitive sensing circuit for inertial sensor

• Main Author: 鍾啟晨
• Other Authors: 曾繁根
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/xey9cy

碩士 === 國立清華大學 === 微機電工程研究所 === 92 === This thesis researched the micro-capacitive sensing circuit for inertial sensor which used to sense poor signal in air bag or navigation. Due to the sensing capacitive signal was extremely small (10-15F), so it needed a noiseless and a high precision circuit for sensing. Thesis introduced typically four type sensing circuit , analyzed the source of nonideal effect and improvement. We chose the differential type of sensing circuit, because this architecture could cancel the common mode noise, stray capacitance and easy to analysis. The first generation of circuit design included of two matching micro-capacitive sensing circuit , noiseless differential amplifier and the input were controlled by two out of phase clock signal. The second generation of circuit design included of two matching micro-capacitive sensing circuit , two stage high gain amplifier. Layout used capacitance match , guard rings to protect core circuit and lower the interfere of EM. The simulation results of first generation circuit showed that output gain was 19V/pF and the total noise was about 1.26 mV. So that the circuit resolution was about 0.7fF, but experiment showed the circuit resolution was about 50~100fF. We knew that the error were due to noise and dc offset. The simulation results of second generation circuit showed that output gain was 190V/pF and the total noise was about 2.7386 mV. So that the circuit resolution was about 10aF.