Based on digital circuit design methods

a signal test circuit is designed by using the capacitance digital conversion chip AD7745 and high-performance ARM micro-controller.The measurement principle of AD7745 and the software and hardware design of circuit are described.AD7745 directly converts capacitance signal into digital signal rather than voltage signal

which can avoid converting the useful signal together with the error signal into voltage signal

and effectively reduces the interference of distributed capacitance and parasitic capacitance in environment.The experimental results show that the signal processing circuit for micro-displacement capacitance sensing improves stability and anti-interference ability of variable pole pitch capacitive sensor

and the resolution of the system is up to 0.72 μm.