Research And Design Of Multi-mode Signal Source Based On Direct Digital Frequency Synthesis

Signal source plays a significant role in the research and development of radar,communication,microwave measurement,instruments and other fields.Recent years have witnessed a spurt of progress in electronic communication technology,the surrounding electromagnetic environment present a state which is progressively complicated and changeable.Therefore,the more stringent requirements for the function and signal quality of the signal source are needed in the research and development of electronic communication system.In order to provide better test support for electronics,communications,radar and other fields,a multi-mode signal source is designed in this thesis based on Direct Digital Fraquency Synthesis(DDS)technology and Field Programmable Gate Array(FPGA)technology.Firstly,the theoretical basis of multi-mode signal source are introduced in this thesis,including commonly used signal waveform model,principle and performance indicator of direct digital frequency synthesis technology and frequency generation control algorithm.Aiming at the problems of high resource consumption and large delay of traditional nonlinear frequency generation control algorithm,a nonlinear frequency modulation algorithm based on time nonlinearity is proposed,which lays a theoretical foundation for the subsequent realization of different types of modulation signals.Secondly,the overall structure of signal source is designed in this thesis based on the indicators analysis of multi-mode signal source.Following the overall design,the hardware circuit and waveform control logic of multi-mode signal source are implemented in this thesis based on direct digital frequency synthesis.The design of signal generation circuit,reference clock circuit,FPGA function circuit and power management circuit are completed in hardware circuit design.For each circuit module,this thesis introduces its chip selection and circuit schematic design in detail.What are the main components of the waveform generation control logic for the multi-mode signal source are the host computer communication module,the data frame decoding module,the DDS function configuration module,the DDS parallel communication module and the most critical waveform generation control module.Based on the working principle of the selected AD9914 and the nonlinear frequency modulation control algorithm proposed in this thesis,the design and implementation of the waveform control logic are introduced in detail.The accuracy of time control of the entire control logic can reach 10 ns,and the frequency setting accuracy can reach 0.7820137 MHz.Combined with the waveform control logic implemented by the nonlinear frequency modulation algorithm proposed in this thesis,the resource consumption of the core logic is effectively reduced,and the implementation cost of the signal source is reduced.Finally,according to the schematic diagram of the hardware circuit design,the PCB layout design of the multi-mode signal source and the processing patch are completed.A multi-mode signal source test and verification platform is built,to test the performance requirements and functions of the signal source.The test results show that the signal source can generate frequencies in the range of 600 MHz to 1.4GHz,the minimum frequency switching time is 80 ns,the stray suppression is better than 55 d Bc and 21 waveforms are generated totally,such as frequency modulation,continuous wave/intrapulse phase modulation and so on,which can be generated to meet the design requirements.