用于三轴MEMS加速度计的集成数字调理电路

Integrated Digital Conditioning Circuit for Three-Axis MEMS Accelerometer

基于0.18μm互补金属氧化物半导体(CMOS)工艺,设计了一种用于三轴微电子机械系统(MEMS)加速度计的集成数字调理电路,实现了三轴加速度信号的数字后处理。该数字调理电路采用级联积分梳状(CIC)与有限冲击响应(FIR)相结合的滤波器形式,有效滤除了带外的量化噪声,提高了输出信号的信噪比;零位采用四阶多项式拟合温补算法,标度因数采用二阶多项式拟合温补算法,有效降低了加速度输出随温度的漂移,提升了加速度计的测量精度。此外,FIR滤波器采用时分复用的实现形式,温补模块采用串行实现形式,有效减小了芯片面积,最终芯片面积为1.5 mm^(2)。测试结果表明,滤波器符合设计值,三轴MEMS加速度计的零偏不稳定性为15μg,速率随机游走为0.035 m/s/√h,温补后零偏全温区变化量为3.55mg,提升了5.4倍;温补后标度因数全温区变化量为0.0026,提升了4.1倍,电路性能良好。

Based on 0.18μm complementary metal oxide semiconductor(CMOS)technology,an integrated digital conditioning circuit for a three-axis micro-electromechanical system(MEMS)accelerometer was designed,achieving the digital post-processing of the three-axis acceleration signal.The digital conditioning circuit adopts the filter form of cascaded integrator-comb(CIC)and finite impulse response(FIR),which can effectively filter out the quantization noise outside the band and improve the signal-to-noise ratio of the output signal.The zero output was fitted with a fourth-order polynomial temperature compensating algorithm and the scale factor was fitted with a second-order polynomial temperature compensating algorithm,reducing the drift of the acceleration output with temperature and improving the measurement accuracy of the accelerometer.In addition,the FIR filter was implemented with the time-division multiplexing method and the temperature compensating module was in serial,which can reduce the chip area.The final chip area is 1.5 mm^(2).The test results show that the filter accords with the design value.The bias instability of the three-axis MEMS accelerometer is 15μg;the rate random walk is 0.035 m/s/h;the drift of the bias over whole temperature after compensation is 3.55mg,which is improved by 5.4 times;and the drift of the scale factor over whole temperature after compensation is 0.0026,which is improved by 4.1 times.The circuit performance is good.