Research On Readout Circuit Of MEMS Capacitive Accelerometer Based On Ring Diode

With the increasing prosperity of the development of the Internet of Things,the important device sensors that make up its parts have ushered in extensive research,especially accelerometer sensors,which are widely used in automotive electronics,consumer electronics,and aerospace.In view of its wider and wider range of applications,the high-performance MEMS capacitive accelerometer readout circuit has become a research hotspot at home and abroad.Through the investigation and research of accelerometers at home and abroad,this thesis uses SMIC(SMIC)0.18?m CMOS process to research and design a MESM capacitive accelerometer readout circuit with high resolution and wide capacitance range.The chip includes Capacitive readout core module(including ring diode C/V conversion circuit and instrumentation amplifier(INA)),low-pass filter,inverting circuit,PI feedback circuit and other sub-modules.In order to achieve highprecision detection of capacitance,this thesis adopts a new type of micro-capacitance detection system based on ring diode demodulation.Through noise analysis and device optimization of the capacitance readout circuit,the overall noise of the chip is reduced and the detection accuracy is improved.Among them,the high-frequency carrier signal modulates the 200Hz?2k Hz capacitance signal to be detected at a high frequency of 1MHz,and then demodulates and amplifies,and then uses a low-pass filter to filter out the high-frequency carrier signal and noise.In addition,an inverting circuit is used to convert the signal into a differential signal,which is output to the analog-to-digital converter at the back to meet the driving capability of the overall chip.At the same time,the PI feedback closed-loop structure is adopted to improve the linearity and accuracy of capacitance detection.Finally,circuits such as buffers and current mirrors are used to provide bias voltage and bias current to the system to ensure the stability of the chip.It can be seen from the simulation results that the accelerometer readout circuit can read the capacitance signal with a frequency of 200?2KHz with a static capacitance range of 5?10p F and a dynamic capacitance of 1?4p F as a proportional voltage signal.In the frequency range of 200?2 k Hz,the chip equivalent input noise can be as low as 659 n V/?Hz,and the capacitance resolution requirement of 5 a F can be achieved.Therefore,the chip design has the advantages of high resolution and wide capacitance detection range,and has huge application scenarios.