Design Of A Readout Circuit For Capacitive Array Pressure Sensor Applications

With the rapid development of sensor technology and flexible materials,the integration of sensor arrays on flexible materials has become a direction of sensor development,and flexible array sensors are indispensable in applications including bionic robots and electronic skin.Readout circuits that act as a bridge between sensors and digital processing systems are also becoming more important.This paper is based on an array of flexible capacitive pressure sensors to complete the design and verification of a multi-channel,sensor readout circuit.This paper describes the related research on the capacitive sensor readout circuit at domestic and foreign in recent years.After analyzing the structural characteristics,advantages and disadvantages of some commonly used capacitance readout circuits,one of the structures is selected as the main structure of circuit.According to the characteristics of sensor,a parallel fully differential capacitance voltage conversion circuit,data retention circuit and single-integration multi-channel analog to digital converter are designed.By optimizing the fully differential structure,the influence of common mode feedback on the capacitance injection is eliminated,and the singleended connection of the non-differential capacitor in the fully differential circuit is realized.For the circuit structure,a fully differential buffer is also designed in this paper.This module realizes the sample and hole function while modulating the common-mode level.To reduce power consumption,the circuit also includes an enable structure that reduces current consumption by switching off unwanted modules during conversion.After investigating the structure of the ADC,the paper decided to use a single-slope integrated structure as main structure.Although this ADC is slower,it can easily expand multiple channels,which is more suitable for the readout of array sensors.The design also includes simple digital logic for timing control of capacitance voltage conversion,ADC,enable and other modules.In this paper,a readout circuit used in a capacitive array pressure sensor is designed based on 0.18 um CMOS process.The ENOB of internal ADC is 9.4bits,the sampling period is 105.6us,and there are 8 effective channels.The capacitance voltage converter adopts switch capacitor,the conversion period is 1.6us,and the input range is 1p~4p.