Research On Noise Analysis And Suppression Of The Charging-Discharging Capacitance Position Sensor Circuit

Space electrostatic accelerometers/space inertial sensors are mainly used for high-precision applications including earth gravity field measurement,space gravitational wave detection,and space experimental test of equivalent principle.The ultra-sensitive capacitive position sensor circuit is the key technology in space inertial sensor,and its measurement accuracy has direct impact on the resolution of inertial sensor.In this thesis,on the application demand of space gravitational wave detection and other deep space detection missions,a simple structured,low power,high precision charging-discharging capacitive position sensor circuit is studied.The principle and noise model of the circuit are analyzed.The main noise sources caused by the voltage of square wave amplitude and the diodes switching circuit are analyzed.Related noise suppression methods are adopted,which reduced significantly the main noise items of the capacitance sensor circuit.Firstly,the fundamental principle of the charging-discharging capacitive displacement sensor is introduced.In the meantime,the noise modeling and analysis are carried out for each part of the sensing circuit,in which the diodes are found to be the largest noise source in the sensing circuit.The noise model from the diode is verified by experiments.At the same time,the paralleled scheme of voltage reference sources is applied to the square wave generating circuit.Theoretical analysis shows that the scheme can reduce the relative voltage noise of the square wave amplitude,and finally improve the capacitance resolution of the sensing circuit.Secondly,the performance of the paralleled reference source and the sensing circuit are measured.Experimental data shows that the parallel reference source scheme achieves the goal of reducing the relative voltage noise.The calibration results of the sensitivity coefficient of the sensing circuit are consistent with the theoretical expectation within the error range.The capacitance resolution of 2.2?10^-7pF/Hz^1/2 at 0.1 Hz,and1.5?10^-7pF/Hz¹/2/2 at 1Hz are achieved.The total power consumption of the sensing circuit is 341mW.All these results basically meet the expected level.Finally,a theoretical analysis and circuit simulation on the multichannel simultaneous operation of the charging-discharging capacitance sensor circuit are carried out,which verified the feasibility of multichannel simultaneous operation and the simulation results are consistent with the theoretical analysis.At the same time,the miniaturization scheme of the sensing circuit is designed preliminarily,including the layout of the circuit board and the choice of electronic component packaging.