Aiming at the work principle of capacitive sensor

a high-precision detecting circuit for microcapacitance measurement using complex programmable logic device（CPLD） is as core

PS021 is used

based on time to digital converter（TDC） technology.The measurement principle of PS021

the design of circuit hardware and software are presented.PS021 and CPLD are used to process the capacitance signal.It makes the circuit simple and easy to application.By setting the internal registers of PS021 through software

high precision measurement is achieved.The experimental results show that the circuit has a good performance with resolution of 8 aF in 10 Hz update rate

the highest update rate can be up to 50 kHz

the resolution ranges 1 fF～ 0.01 aF

and the effective number of precision bits（ENOB） is up to 22 bits.The high precision and high update rate can ease the contradiction between measurement speed and resolution.And the design improves the measurement precision of micro capacitance.