Design And Implementation Of High-precision And Phase-controlled Direct Digital Frequency Synthesizer Based On FPGA

The direct digital frequency synthesis is a whole new, fully digital frequency synthesis technology. it is a new revolution coming after direct frequency synthesis, phase-locked frequency synthesis. The technology has been applied to meter, radar, satellite and remote telemetry timing and many other fields. Along with the rapid development on the technology for microelectronics and the continuous improvement of devices processing, the direct digital frequency synthesizer(DDS) has become the best in the field of frequency synthesis. It has the advantages of high frequency resolution, fast frequency switching speed, the error ability to maintaining constant phase while switch frequency, low phase noise and easy integration. And the conventional frequency synthesizer cannot be compared with the DDS.There are three synthesiers that is achieved by FPGA in this design. And the 10 MHz reference signal is provided by rubidium oscillator which has ultra-low phase noise and ultrahigh frequency stability. This system can output two 10 MHz signals and one 5 MHz signal and their stability remain unchanged. A typical DDS consists of phase accumulator, waveform memory, digital to analog converter and a low pass filter. The design further increases the frequency multiplier circuit and the output drive circuit because it is used in high-precision satellite timing system and to drive TTL level.Firstly, the historical development of frequency synthesis is outlined, and then the paper describes the principles and structure of the DDS in detail and analyses its performance. Secondly, it analyses the spurious noise that resulted from phase truncation, quantization error and non-ideal characteristic of DAC. And several more practical methods to reduce the spurious is proposed. Then it briefly analyses the spectrum of the output signal. Thirdly, the paper briefly introduces X3S1400AN-FGG676 of Spartan-3an series FPGA made by Xilinx Inc. Focusing on the specific method of DDS based on FPGA and the entire hardware circuit, the paper gives the RTL schematic of every software module and the schematic of every hardware module. Finally, the product subjected to a number of severe tests and the measurement result is also presented.The test results show that the frequency stability is 1.6×10-11 at one second and can reach 3.6×10-12 at ten seconds. And it can prove that utilizing a Rubidium Frequency Standard and the DDS based on FPGA can output high-precision frequency references.