Research On AC Quantum Voltage Synthesis Technology Based On Josephson Effect

The development of science and technology and military industry has put forward higher requirements for the voltage reference in the field of measurement.The traditional AC voltage standard uses a thermoelectric converter to achieve traceability and precise measurement of voltage.As a physical reference,its performance is susceptible to drift due to external influences.In recent years,the quantum voltage reference based on the Josephson effect has quickly become a research hotspot of metrology institutions in various countries because of its excellent stability and strong reproducibility.My country has successfully established 1 V and 10 V DC quantum voltage benchmarks in the 1990 s.Its uncertainty reached the international advanced level at that time,but the synthesis of AC quantum voltage is still in the exploration stage.This paper relies on the experimental platform of the Chinese Academy of Metrology to carry out research on AC quantum voltage synthesis technology.The main research contents as follows:1.Briefly introduce the Josephson effect and the generation and development of quantum voltage,and expound the advantages and development prospects of quantum voltage reference over traditional physical voltage reference.The principle of traditional Josephson voltage reference,programmable Josephson voltage reference and pulse-driven AC Josephson voltage reference are detailed,and the advantages and disadvantages of these three voltage references are compared and analyzed for the subsequent synthesis of AC quantum voltage Provide a theoretical basis.2.Evaluate the temperature stability of a programmable quantum voltage synthesis system based on a small refrigerator,test the trend of critical current value with temperature and the relationship between operating margin and microwave power and temperature,and find the optimal operating parameter of the system: temperature It is 9.9K and the microwave power is 6dBm.The working conditions of Josephson array in pulse-driven quantum voltage synthesis system based on liquid helium refrigeration technology were studied,and the relationship between AC-DC I-V characteristics,microwave frequency and microwave power and maximum operating margin was tested.After comprehensively comparing the test results of the two systems,it was finally decided to select a pulse drive system for the synthesis of AC quantum voltage signals.3.The key technologies in AC quantum voltage signal synthesis are studied.A compensation current source circuit based on the principle of DDS is designed,a MATLAB program is written to generate waveform data,and a sine wave with adjustable output frequency and amplitude of the AD768 digital-to-analog conversion chip is controlled by FPGA;?-? generated pulse modulation is studied and working principle of the type parameters effect the performance of the modulator,including the generation of quantization noise in the modulation process,noise shaping technology,oversampling,etc.,shows the modulation implementation process in detail,and analyzes the impact of the number of levels and the order on the performance.Innovative results:At present,the domestic research on the pulse-driven AC quantum voltage system is in its infancy,and the effective value of the synthesized signal does not exceed 10 mv.In this paper,the pulse-driven method is used to successfully synthesize the AC quantum voltage signal with an effective value of up to 90 mv.The frequency spectrum of the pulse pattern,compensation current source and AC quantum voltage waveform in the process of signal synthesis is analyzed.The harmonic distortion is lower than the fundamental frequency signal by 100 dBc,which meets the requirements of Josephson quantization.It has the potential for further research on AC quantum voltage.Important practical significance.