Development of High-precision Dual Integration AD Converter based on MCU and FPGA

In the design of high-precision A/D converters, the dual-slope A/D conversion circuit has the advantages of a simple structure and good linearity. However, existing dual-slope A/D converters suffer from the drawbacks of inaccurate control of integration time and inflexible usage. In this paper, a control circuit based on field-programmable gate array (FPGA) devices, along with an operational amplifier with low offset voltage and a comparator with low bias voltage, is designed. A high-count rate counter is also employed. Additionally, the entire system is intelligently controlled by a microcontroller. These measures achieve precise and controllable integration time, conversion resolution better than 14 bits, and conversion accuracy with nonlinearity error less than 3 least significant bits. Through field testing, the dual-slope A/D converter has been successfully applied in an RLC digital bridge testing system, allowing for different integration times to be set based on the test frequency and meeting the requirements of practical applications.