Research On The Frequency Synthesis For FPGA-based Atomic Clock

With the rapid development of science and technology, there is significant demand on the time accuracy and stability. The conventional atomic clock, which is so bulky that cannot widely be used in military aerospace and national defense, is still not perfect and need to be improved, although its accuracy has reached 10-15. Then it is critical to develop miniaturized atomic clock with high precision and stability that may help China not be left behind in an intensive competition, where the United States and Japan are currently ahead of us.It is necessary to understand the internal structure at first and then to miniaturize atomic clock. The atomic clock system is divided into two parts: physical part and circuit part. It is important to miniaturize the physical part and the circuit part of the atomic clock may cause the breakthrough. DDS (Direct Digital Frequency Synthesis) is one of the main cores modules in the circuit. One of the tasks of the project is to use dedicated DDS chip to achieve the circuit; and it is obvious to apply FPGA (Field Programmable Gate Array) to replace four DDS chips in the circuit. This paper introduces the method of FPGA-based DDS circuit to miniaturization. The specific contents are as follows:Firstly, the theory and the classification of DDS were briefly discussed, then the role of various modules in DDS and the output spectrum were presented, the reasons were analyzed that induced output stray.Secondly, the EDA design flow was presented, Verilog HDL (Hardware Description Language), FPGA and Quartus II were briefly introduced, the type of FPGA was finally decided.Thirdly, the method of FPGA-based DDS was proposed and the structure of 137Hz single frequency and 100MHz FM (Frequency Modulation) output was designed, the program had been compiled, and a 9th-order elliptic low-pass filter was designed and improved.Ultimately, the waveform output was simulated by ModelSim, and the spectrum was analyzed by Matlab, the consistency of spectrum was validated at last.