Research Of Analog To Digital Conversion Circuit Based On Digital Potentiometer

Digital potentiometer is a digitally-controlled electronic component built from a resistor ladder integrated circuit that mimics the analog functions of a potentiometer.Compared to the traditional mechanical potentiometer, digital potentiometer is more flexible by using digital signals and switches controlled by a microcontroller or logic circuit instead of mechanical action. Digital potentiometer can be used to control an analog signal digitally by changing the resistance according to the input voltage at the interface.Bridge circuits are widely used in the electrical power system and fine measuring instruments due to their simple structure, wide measuring range, high sensitivity, good linearity and easiness to realize temperature compensation. Digital potentiometer is now often used to achieve automatic balance of bridge circuit, however, the variation of voltage of bridge arms cannot be real-time monitored during the bridge balancing process thus the interference signal which causes the imbalance of bridge arms cannot be detected and quantitatively analyzed. In this thesis, digital potentiometer and microcontroller with their peripheral circuits were used to achieve the automatic balance of the bridge circuit. and realize analog-to-digital conversion. The voltage change of the bridge arms resulting from the interference was detected by a high precision voltage comparator and converted to digital signal by the digital potentiometer with successive approximation method. The designed circuit can be used for the automatic balance of bridge circuit, quantification of the interference signal,analog-to-digital conversion and optical or temperature sensor.In this thesis, high precision voltage comparator AD790 K and digital potentiometer Maxim5483 were used to measure the voltage difference of two bridge arm and convert the data to digital signal. Since the resistance variation of digital potentiometer is not continuous, a lot of experimental data were collected for statistical analysis during software design to increase the accuracy and stability of the circuit. An online systemprogrammable circuit was also used to facilitate the download of program, real-time monitoring and human-computer interaction.After optimization, the system has a conversion rate of 226 ~ 926 ?s which can be improved further by increasing the MCU clock frequency, a dropped bit of n 'Max 1.56 LSB and a ENOB of 8.44. The designed circuit in this thesis exhibit advantages in operating speed, accuracy, stability and multi-application in the field of automatic balance,A/D conversion and environmental sensors compared to conventional automatic balance bridge circuits.