Design Of Low Noise Preamplifier And Bias Circuit For Mems Microphone

With the rapid development of wireless communication technology, consumer electronics products increasingly miniaturization, lightweight and highly integrated. For these products, the design of the acoustic input part of the circuit is faced with the similar requirements. Compared with the traditional electret condenser microphones, MEMS microphones have many advantages such as small volume, low cost, good consistency, high temperature resistance, resistance to vibration, process repeatability, easy to be volume-produced, easy to be integrated and so on, that makes it a currently popular in the design of consumer electronic products, design application-specific integrated circuit also become very important.This project comes from Chiphomer Technology(Shanghai) Limited, the name of the project is CPM211, the main content is using umc35 cdmos technology to design an application-specific integrated circuit chip for a MEMS microphones chip which is produced by Omron Corporation,. This chip contained a low noise preamplifier circuit and a bias circuit.Low noise preamplifier has the impedance convert function, it can improve the drive ability of the output signal of the MEMS microphone and make the power amplifier of the next level works normally, the low noise technology can also further reduce the signal to noise ratio loss. The bias circuit is mainly composed of a oscillator and a charge pump, the output of the bias circuit is a 15 V bias voltage which is used to drive the MEMS microphone to work normally.This thesis introduces the purpose and significance of the topic at first, and then introduces the history of microphone, which focuses on the related electrical parameters of capacitive MEMS microphones, it provides a reference for us to formulate the design target. As the frame and basis of the circuit design, the system architecture and theoretical basis of the Low Noise Preamplifier and Bias Circuit for MEMS microphone occupies a quarter of the space in this thesis. The emphasis of this thesis introduces the diagram of low noise preamplifier circuit and bias circuit, and presents the process and result of using simulation tools to simulate every modules. Considering the integrity of the circuit design process, this thesis makes a general introduction of layout design process and some factors which need to be considered importantly in layout design. After the MEMS microphone chip and the low noise preamplifier and bias circuit chip were packaged into a single chip in the foundry, this chip’s performance will be tested and the test results will also be described in detail.The test results show that the overall current of the single chip is 160μA, its sensitivity is-42 d B, frequency response curve smoothing, SNR is 60 d B, THD is less than 0.2%, bias voltage is 15.2V, the gain of the Low Noise Preamplifier is 4.5d B. The test result can meet the requirement.The MEMS microphones preamplifier circuit and bias circuit which is provided by this project has so many advantages such as low noise, highly DC-DC booster conversion efficiency, low power consumption, it is a consumer electronics products which has strong practicability.