| High resolution and high-precision digital to analog converter is one of the main research contents in the field of precision measurement in the world.For a long time,the development of high-precision digital to analog converters with advanced performance has been concentrated in some well-known foreign enterprises,such as TI,Agilent,fluke,etc.there is relatively little research in the field of high-precision digital to analog and analog-to-digital conversion in China,and almost all the high-precision instruments and meters used in the field of precision measurement rely on imports.Therefore,the independent research and development of high-precision digital to analog converter is of great significance.At present,although the traditional Kelvin Varley digital to analog converter can provide high output accuracy,the converter has large volume,complex structure and high cost;Another commonly used digital to analog converter is R-2R digital to analog converter.The resistance switch network used in the converter is complex,the calibration rate is low,and the digital to analog conversion accuracy is directly subject to the accuracy of the resistance used,which makes it difficult to improve the subsequent accuracy of the circuit.The above two digital to analog converters have some key problems that are difficult to solve in realizing high-resolution and high-precision performance,so they are not suitable for precision measurement and linearity test of electric measuring instruments.A high-precision digital to analog converter with low cost,simple structure,high calibration rate and good performance is urgently needed in the field of measurement and calibration in China.To solve the above problems,a low-cost and high-precision voltage output digital to analog converter is designed and developed in this paper.The high eight bit weight bit circuit of the digital to analog converter is composed of binary resistance proportional voltage divider,and the resolution of the digital to analog converter is expanded by commercial digital to analog conversion chip.Through the reasonable layout and selection of main devices such as resistors and switches in the high eight position switching resistance network,the calibration of the whole high-precision digital to analog converter is automated by using embedded system combined with summation compensation circuit,sampling circuit and millisecond measurement method.The high-precision digital to analog conversion circuit with self-calibration designed in this paper is easy to realize,and has the following advantages:（1）The error of resistance accuracy used in switched resistance network can be self-calibrated by millisecond measurement method,which reduces the accuracy requirements of instruments such as reference source and digital voltmeter,saves the cost in precision measurement,and has great accuracy advantages.（2）The circuit adopts the combination of voltage divider and digital to analog conversion chip.The circuit has high integration and the overall volume of the system is small.Combined with the embedded system,the whole self-calibration process is automated and the calibration speed is fast,which improves the work efficiency in the fields of electromagnetic measurement,instrument accuracy evaluation and so on.In addition,the error of the system is analyzed in detail,and the optimized system is calibrated.The data parameters after error calibration are corrected and compensated by commercial digital to analog conversion chip.The results show that the output input ratio of the whole system is close to the theoretical value.The host computer test program is compiled to complete the system joint debugging,and the output proportional accuracy and stability of the digital to analog converter are tested.The test results show that the effective resolution of the designed digital to analog converter is 21 bits,and the output proportional accuracy is better than 3×10-7 order of magnitude. |
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