高线性度全差分四阶ΣΔ微加速度计接口ASIC

High Linearity Full-Differential Fourth-Order ΣΔ Interface ASIC for Micromachined Accelerometer

为了降低电容式Sigma-Delta(ΣΔ)微机械(MEMS)加速度计的量化噪声,减小开关电荷注入和衬底噪声共模干扰,减小谐波失真,设计了一种全差分四阶ΣΔ加速度计的接口专用集成电路(ASIC)。提出了一种简单、有效的全桥平衡结构,减小了驱动信号变化时,运放输入共模的变化对电路的干扰;提出了双侧反馈结构,大大提高了系统线性度。设计完成了电荷积分器、全差分前置补偿电路、二阶积分器等电路。采用0.5μm两层金属两层多晶n阱CMOS工艺流片,测试结果显示:闭环系统噪声密度为75μg/Hz^(1/2),系统灵敏度为1.32 V/gn,非线性度0.085%,功耗40 m W。结果显示本次设计满足微加速度计接口电路的设计要求。

A full-differential four-order sigma-delta（ΣΔ）interface ASIC for capacitive micromachined accelerome-ter is presented to reduce quantization noise,switch charge injection,common mode disturbance of substrate noiseand harmonic distortion. An effective simple full-bridge equilibrium architecture was brought forward to reduce thedisturbance induced by the variation of common mode voltage of operational amplifier,when the driving signal alter-nating. To enhance the linearity of system,bilateral static force feedback was employed. Charge integrator,full-differential lead compensator,second-order integrator etc. were designed. The circuit was fabricated in 0.5 μm two met-al two poly n-well CMOS technology. The tested results indicated that the closed-loop noise density was 75 μg/Hz^1/2,sensitivity was 1.32 V/gn,nonlinearity was 0.085% and the power dissipation was 40 m W.All these properties metthe design requirement of micromachined accelerometer.