Design Of Low Phase Noise Frequency Agile Rate Source Based On FPGA Control

In modern times,with the rapid development of science and technology,in the fields of electronic countermeasures,radar reconnaissance,aerospace,wireless communication,remote sensing and telemetry,the technical requirements of frequency source synthesis technology and fast frequency hopping become higher and higher.At present,the performance index of frequency source synthesis technology is far from higher performance requirements,which also restricts the development of radar detection and ultra-high-speed frequency hopping communication in China.At present,high frequency band,high frequency stability,wide frequency band,low phase noise,low spurious,fine step,ultra-high-speed frequency hopping and high output power become the target of frequency source synthesis technology.In this thesis,three techniques of frequency source synthesis are introduced firstly.They are phase-locked frequency synthesis,direct digital(DDS)frequency synthesis and direct analog frequency synthesis.At the same time,the advantages and disadvantages of three kinds of frequency synthesizers,namely,phase-locked frequency,direct digital synthesizer(DDS)and direct analog synthesizer,are compared.Combining the advantages and disadvantages of three kinds of frequency synthesizer,the application characteristics of three kinds of hybrid frequency synthesizer schemes,namely,DDS-PLL,DDS-PLL external mixer and downconverter-PLL,are studied.The working principle and basic structure of DDS technology are introduced.The phase noise analysis of DDS technology and the effects of amplitude and phase,analog-to-digital conversion,clock and other factors on DDS spurious are analyzed.Then,according to the actual situation of the subject and the requirements of related technical indicators,the frequency source system scheme is designed,and several different design schemes of the subject are given.By comparing and selecting several different schemes,the advantages and disadvantages of them are analyzed.Finally,the frequency synthesis method of DDS+PLL is adopted.This scheme fully combines the advantages of DDS,such as high frequency resolution,fine step,low phase noise,fast frequency change and easy control,and combines with the good tracking and filtering characteristics of PLL.By controlling the functional pins of DDS chip with FPGA,DDS can output different frequencies under the control of the clock,so that the PLL can output different frequencies and continue to switch to the next frequency after a certain period of time,which realizes the agility well.In the aspect of software function realization,according to the project,the chips used in the hardware circuit of DDS are selected,the modules of clock signal and peripheral circuit are designed,and the layout and wiring of PCB layout of DDS are reasonably designed.Finally,the software of communication control between FPGA and AD9910 is designed and developed,and the system test is carried out to fulfill the requirements of the project..