Analysis And Circuit Optimization Of Distributed Capacitance In Differential Capacitance Measurements

Accelerometers and other inertial navigation devices have important application value in the field of navigation because of they are not susceptible to radio interference,do not need an external reference to complete navigation,and are insensitive to the external environment.Capacitive sensors are widely applied in the field of sensors due to their advantages such as simple structure,high sensitivity,fast response speed and insensitivity to temperature changes.Based on the quartz flexible accelerometer platform,this paper analyzed the effect of distributed capacitance of the differential capacitive sensor and mainly completed the following works:The accelerometer structure and its internal differential capacitor components were described.Analyze several commonly used differential capacitance measurement circuits.Based on the theory of capacitive coupling between conductors,a distributed capacitance model was established based on the position of conductors inside the accelerometer.The distributed capacitances in the charge-discharge differential capacitance measurement circuits were also analyzed and modeled.A distributed capacitance measurement scheme was designed to measure the data required to calculate each capacitance by using the measurement function of the circuit itself without changing the original circuit structure.Based on the data,the distributed capacitance values are roughly calculated to verify the established model.According to the established distributed capacitance model,the effects of coupling,noise,zero deviation,and non-linearity that may be caused by distributed capacitance in different positions of the circuit are analyzed and calculated.To suppress the effect of distributed capacitance on the measurement results of differential capacitive accelerometers,the idea of circuit optimization is proposed,and the optimization scheme is designed based on the charge-discharge scheme.In terms of hardware,equipotential shielding is used to shield the connection lines from the accelerometer to the measuring circuit.In terms of algorithms,a four-cycle sampling algorithm was proposed.By controlling the capacitances connected in different measurement stages to obtain a number of related measurement results,thereby suppressing the influence of distributed capacitance,and calculated the differential capacitance difference without distributed capacitance.The experimental comparison with single-cycle measurement schemes shows that the four-cycle sampling scheme suppresses the zero offset to 4%of the single-cycle measurement scheme,and the effect on the distributed capacitance can be suppressed to less than 3%of the original distributed capacitance value.