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在分析电容式MEMS麦克风工作原理的基础上,提出了一种用于电容式MEMS麦克风的读出电路。该读出电路包括低极点频率的高通滤波器和低噪声单位增益缓冲器,高通滤波器用来读出MEMS麦克风在声压作用下产生的小信号,单位增益缓冲器用来隔离高通滤波器和后续信号处理电路,并提供较大的驱动能力。仿真结果表明,当电源电压在1.2～3.6V之间时,读出电路都可以正常工作,且静态电流小于60μA,等效输入噪声为5.2μV,电压增益大于-1.56dB(83.6%)。由于消除了失调电压的影响,电路可以处理幅度范围为50μV～200mV的小信号(参考X-FAB 0.35μm CMOS工艺)。
On the basis of analyzing the working principle of capacitive MEMS microphone, a readout circuit for capacitive MEMS microphone is proposed. The readout circuit includes a high-pass filter with a low pole frequency and a low-noise unity gain buffer. The high-pass filter reads out a small signal generated by the MEMS microphone under sound pressure. A unity gain buffer is used to isolate the high-pass filter and the subsequent signals Processing circuit, and provide greater driving ability. The simulation results show that the readout circuit can work normally when the supply voltage is between 1.2 ~ 3.6V, the quiescent current is less than 60μA, the equivalent input noise is 5.2μV and the voltage gain is greater than -1.56dB (83.6%). By eliminating the effects of offset voltages, the circuit can handle small signals in the range of 50μV ~ 200mV (refer to X-FAB 0.35μm CMOS Process).