适于MEMS加速度计读出电路带宽可调的低通滤波器

A Low Pass Filter with Adjustable Bandwidth for MEMS Capacitive Accelerometer Readout Circuit

提出了一种适于MEMS电容加速度计读出电路带宽可调的低通滤波器,带宽调节范围为100～8000kHz。信号频率低于500Hz时选用开关电容低通滤波器,高于500Hz的信号则由连续时间低通滤波器来处理。该低通滤波器采用1.2μm的2P2M的N-阱CMOS工艺实现。设计中分析并解决了因时钟信号引起的制约开关性能的因素:优化的开关时序消除了电荷注入引起的非线性;时钟馈通敏感节点增加虚拟开关抵消了耦合电荷;高PSRR共源共栅折叠式差分输入结构,有效地抑制了来自电源的干扰,改善了电路的性能。

This paper describes a low-pass filter with adjustable bandwidth range from 100 Hz to 8 kHz for MEMS capacitive accelerometer readout circuit. The signals with their frequencies lower than 500 Hz are filtered through the switched-capacltor low- pass filter, while those higher than 500 Hz are filtered through the continuous-time one. This low-pass filter was implemented with 1.2 ktm 2P2M N-well CMOS process. Problems such as charge injection and clock feedthrough caused by turning off swithes are analyzed and solved in this design. The optimal switch sequence helps eliminate the nonlinearity caused by the charge injection ; the addition of dummy switches to sensitive nodes caused by the clock feedthrough can greatly reduce the coupled charge; and the use of high PSRR folded cascode differential input stage can restrain the interference from the power supply. The circuit performance, therefore, has been greatly improved.