Noise Analysis And Design Of High Precision Fully Differential Capacitive Micro Accelerometer Interface Circuit

Capacitive accelerometers convert weak acceleration signals into detectable electrical signals.High-precision accelerometers are widely used in seismic detection,automotive safety,aerospace,and automation industries.The accelerometer interface circuit is an important part of the acceleration sensor and has the important significance of realizing the practical use of the sensor.In view of the deficiencies in the current theoretical research and interface circuit design of capacitive micro-accelerometer,the paper mainly accomplishes the following tasks: noise analysis and circuit optimization of capacitive micro-accelerometers,and proposes targeted noise reduction measures;system architecture and module design of interface circuits and improvement of performance and parameters;layout design of interface circuit and comprehensive testing of accelerometer systems.In this paper,the noise characteristics of the capacitive micro-accelerometer are analyzed in detail,and various noise reduction methods are proposed: the offset and nonlinearity of the sensor's sensitive structure are calibrated by the capacitor compensation array,and the switched capacitor circuit is used to eliminate the influence of parasitic capacitance.The correlated double sampling eliminates low-frequency noise and offset voltages in the circuit,and proposes measures to reduce the thermal noise and flicker noise of the operational amplifier and provide targeted guidance for circuit design optimization.According to the problems in the related research,the new structure of the high precision fully differential capacitive micro accelerometer interface circuit designed in this paper is proposed,including capacitor voltage converter,programmable gain amplifier and fully differential Sallen-Key low pass filter.Based on the analysis of the limitations of the traditional capacitor-voltage converter,an improved scheme is proposed.The overall conversion circuit still adopts the output with single-ended connection,and the fully differential circuit structure is realized by time division multiplexing.and the influence of parasitic capacitance is eliminated by switched capacitor circuit.The programmable gain amplifier can make the interface circuit suitable for different sensitive structures,realize multi-range detection,realize fully differential structure through clock control,and complete the transition from discrete signal to continuous signal.Fully differential Sallen-Key low-passfilter uses fully differential amplifier to realize fully differential filtering.The new structure can save more than 50% of the power consumption and achieve adjustable cut-off frequency,so that acceleration of different frequencies can be detected.The overall circuit adopts a fully differential structure,which effectively suppresses zero drift and harmonic distortion,and reduces common mode interference caused by switching charge injection and substrate noise.The main signal paths eliminate low frequency noise and offset through correlated double sampling techniques.The interface circuit designed in this paper adopts 0.18?m CMOS process flow chip,chip area is 3mm×1.3mm,and it is comprehensively tested with sensor sensitive structure.The test results show that the overall acceleration system has a range of ±2~±200g,a power supply voltage of 3.3V,a total system power consumption of 9.9mW,a nonlinearity of less than 0.2%,a bandwidth greater than 300 Hz,and an operating temperature range of-55~125°C.High precision,high sensitivity,low zero offset,low noise and other high quality performance.The high-precision fully differential capacitive accelerometer interface circuit designed in this paper has important research significance and broad application prospects.