Signal Processing Circuit’s Design In MEMS Digital Microphone

With the development of science and technology, many consumer electronic products toward the high-tech, intelligent, integrated, miniaturized and multifunctional of direction. At the same time, many emerging high-tech products have emergence, such as smart glasses, portable and wearable devices,VR and so on. The microphone plays an important role in the consumer electronic devices, but with miniaturized and multifunctional development, traditional ECM electret microphone has been difficult to meet the requirements, compared with the traditional ECM microphone, MEMS microphone breaks through the many limitations of ECM microphone, with its superb audio acquisition system, resistance to high temperature and temperature stability, small size and anti-jamming performance makes it gradually be popular in the major manufacturers and consumers of all ages. Thus, MEMS microphone has gradually become microphone market mainstream.MEMS microphones generally require one or several signal processing circuit to readout the signals, which need a charge pump circuit to produce stable high voltage; and a signal pickup circuit and proportional amplifying circuit to pick up the weak electrical signal; for the MEMS digital microphone and need a high accuracy of sigma delta A/D conversion circuit.This paper propose a novel charge pump structure on the basis of the traditional pump with a level clock multiplier circuit, which can produce a stable output voltage in a wide range of supply voltage, and the voltage deviation is less than ±5% in all process corners. This design using the source follower and proportional amplifier to pick up the weak electrical signals produced by the MEMS devices; using a proportional amplifier with high open-loop gain to ensure the accuracy of the closed loop gain. Then the paper analyzes the SIMULINK modeling and the main non ideal factors of the three order Sigma-delta modulator, and guides the design of the circuit through modeling and simulation. The last part of this article is the Sigma-delta modulator circuit level design, mainly includes the main sampling switch, amplifiers in integrator, comparator circuit design and simulation. The simulation results show that the design of the circuit can meet the requirement of system performance.