Comparison And Analysis Of Two Kinds Of Signal Extraction Capacitance Micro-displacement Sensing Circuits

The capacitance micro-displacement sensor is one of the key subsystems in international and domestic gravity apparatus and laser interferometer space antenna(LISA)pathfinder(LPF)satellites.Due to their simple structure and potential high resolution,the capacitive transducer with differential transformer bridge is widely used in real-time monitoring of gravity changes and gravitational wave detection.Based on weak signal extraction in different ways,the paper designed two kinds of capacitive micro-displacement transducer—fixing and moving electrode signal extraction types,and theoretical and experimental simulations have been done.Theoretical results: the sensing bias models suggest that the main factors influencing the front end circuit asymmetry were the following several aspects: the asymmetry of transformer winding,the asymmetry of transformer primary to secondary couplings,the asymmetry of bridge resonance tuning capacitors and the asymmetry of actuation filter capacitors;the transfer function models show that two kinds of transformer bridge and trans-impedance amplifier(TIA)circuits have a linear relationship with the central electrode displacement,and the function of the fixing is more complicate than the moving,the TIA noise model of bridge indicates that there exist bridge thermal noise,feedback impedance thermal noise and operational amplifier voltage and current noise,and the noise gain is presented in the end.Experimental results: the sensitivity coefficients of two kinds of circuits are in good agreement with theoretical calculations by collecting and fitting output signal of sensors,it was proved that the theory of system designing was reasonable.Compared experiment data processing with the theory noise formula,results showed that the following several aspects mainly influencing the noise level: the frequency of pumping voltage,the amplitude of pumping voltage,the temperature of the experiment environment,the value of resonant capacitance and the value of nominal capacitance.In the end,analyzing and verifying two kinds of circuits in terms of theoretical and experimental results,advantages and disadvantages and some advice were given in actual applications.