Design And Implement Of Low-Noise MEMS Microphone Interface Circuit

With the rapid increase in the market demand for electronic products,MEMS microphones gradually replace the electret condenser microphones with smaller,lower cost,higher integration,stronger shock resistance and stronger heat resistance,becoming the trend of microphone applications such as consumer electronics,medical care,automotive,audio and radio.Therefore,the design of the MEMS microphone interface circuit has become very important.This thesis is based on a MEMS microphone named E2120 M produced by Infineon Technologies to design three kinds of MEMS microphone interface circuit.The output signals of the two interface circuits are analog signal.The interface circuit of analog signal output is classic interface circuit and positive feedback interface circuit,respectively.It mainly includes the bias circuit and pre-amplifier.The output signals of another interface circuit is digital signal.It mainly includes the bias circuit,differential output pre-amplifier and sigma-delta ADC.The main research contents and results of this thesis are as follows:1.In the bias circuit,current reference structure is used to be adapted to a wide supply voltage range of 1.5V~5.5V,and the circuit can work normally with a very low supply voltage of 1.5V.In order to reduce noise,first eight stage of the charge pump uses the optimized Latched charge pump,and the output stage of the charge pump adds an additional clock,suppressing charge leakage,thereby reducing noise.In order to reduce chip area,traditional RC filter is abandoned,eliminating ripple and reducing noise.2.In the classic pre-amplifier,the reading signal module uses negative feedback loop and triodes to optimize the noise,and the equivalent input noise is only 18.64 n V /(?) at a frequency of 1KHz.The amplification module uses the structure of feedback class-AB output stage.It can work normally at a very low supply voltage of 1.5V and limit the minimum current of both output transistors.Based on the results of simulate,the minimum current emulation is 37?A.3.In the positive feedback pre-amplifier,a positive feedback loop is used to amplify the signal in the first stage,reducing the equivalent output noise of the circuit.At a frequency of 1KHz,the equivalent output noise is only 181 n V /(?).4.In the digital signal output interface circuit,the modulator uses a feed-forward fourth-order single-loop single-bit sigma-delta ADC structure to eliminate the signal components in the loop filter.The oversampling ratio is 128,and the SNDR of the sigma-delta ADC is as high as 100 d B according to the simulation results.The circuit is designed based on Dongbu Hi Tek 0.18?m 1P3 M BCD process.A low-noise MEMS microphone interface circuit using the classic pre-amplifier has been used for layout and tapeout.The chip and MEMS microphone have been packaged together to be tested.Test results show that the circuit can achieve sensitivity of between-24 d B and-26 d B,SNR of 62 d B,power consumption of 210??,and THD+N of less than 0.2%.The test results show that this design meets the requirements of low-noise MEMS microphone interface circuit.