Study And Design Of Conditioning Circuit For Capacitive MEMS Microphone

The consumer electronic products trend to be miniaturized and integrated. Theiracoustic parts have to be made smaller as well. Compared to traditional electretmicrophone, MEMS (Micro-Electro-Mechanical-System) microphone has smaller size,lower cost and better performance. Because of its great advantage, MEMS microphone isbound to be more widely used.Due to the capacitive MEMS microphone chip needs a biasing circuit with outputvoltage of10volt to12volt to drive the capacitive MEMS microphone chip and alow-noise readout circuit with high input resistance to readout the small signal generatedby the MEMS microphone chip in response to the received sound pressure, theconditioning circuit has to be specially custom designed and usually each MEMSmicrophone consists of one capacitive MEMS microphone chip and one conditioningcircuit chip and they are putted into one package.This thesis has six chapters, their main contents read as follows. In chapter1,introduction to the background of conditioning circuit；In chapter2, review of the principleof the capacitive MEMS microphone and its simplified electric model was discussed；Inchapter3, based on the constraints of subject and related references, the structure of theconditioning circuit for the capacitive MEMS microphone was investigated and chosen；Inchapter4, design and simulation of the conditioning circuit in the transistor-level weregiven in accordance with the requirements of performance； Chapter5discuss the designand verification of the layout；And in chapter6, the achieved results were summarized andfuture work was discussed.The conditioning circuit is designed based on the XFAB0.35μm CMOS process. Thesimulation results show that the conditioning circuit can work properly for the powersupply between1.6V and3.6V. When the power supply voltage is3.6V, the output of thebiasing circuit is10.66V with a output noise of0.14nV；The equivalent input noise of the readout circuit is5.2μV；The small signal which has a range of amplitude between50μVand200mV can be readout by conditioning circuit properly；The static power consumptionof the whole conditioning circuit is less than0.45mW.Low noise，high efficiency of DC/DC conversion and low power consumption are thefeatures of the proposed conditioning circuit in this thesis. As only few previous work onthe conditioning circuit for capacitive MEMS microphone is reported, it is believed that thedesign proposed in this thesis can be a good reference.