Research And Design On Double Close-loop Controlled Precision DC Signal Source

In scientific research and electronic products testing, various signal sources are needed.They can offer voltage or current signal for electronic system to measure the parameters.This article describes a way to design a DC voltage source,which can output 0-10 V adjustable voltage and achieve 0.01% accuracy.This method takes 4 12 bits DAC stack to achieve high precision conversion and regulates the output through MCU,besides,it builds a feedback module by using external 24 bits resolution A/D converters to construct a close- loop system,which improved the accuracy of the system effectively.The hardware design of voltage source in this article can be divided into several parts,such as power module,keyboard and d isplay module,RS232 module,reference voltage source, D/A and A/D converter,amplifier module,and MCU module. In detail,the article introduces the working p rinciple of each module and process of circuit designing.To guarantee system precision, the reference voltage of D/A and A/D chip is provided by external resource.the close- loop circuit is constructed by the high resolution ADC, Calibration data stored in external 32KB*8bit EEPROM,Additionally,all operational amplifier has low offset voltage to ensure the stability of output.Software control is realized by MCU and programmed with language C. including key and display module,D/A and A/D controlling module and output adjusted module.the main program is designed into a state machine,check mode,output mode and stop mode respectively. In check mode,the system samples 80 groups of data to set up the correction table;in output mode,to output user’s setting value,the system call the correction data in the table to complete output adjustment by adopting PID algorithm and display the value on OLED screen.in stop mode,the system stop the value output by closing ADC channels.Through PC BA debugging and voltage testing,the DC signal source achieved 0.01% accuracy and voltage output is stable.It has advantage of high prec ision,simple operation, low cost and not only applicable to test circuit,but also satisfy some instruments that need high-precision direct voltage.