Design Of Modulated Signal Generator Based On DDS And Implementation On FPGA

With the development of digital circuits and microelectronic technology,signal generator is being widely used in radar,communication,navigation,electronic countermeasure and instrument and apparatus.During actually practices,users have increasingly strict requirements on resolution,spectrum purity and the frequency range of the signal generator.The high precision signal generator based on Direct Digital Synthesis(DDS for short)has been a solution to many technological problems in previous signal generators.Based on the research and summary of domestic and foreign relevant theory and design method,The paper has improved the structure of the iterative CORDIC algorithm and conceived the algorithm that adjustable duty ratio of square wave and triangle wave;Laid a theoretical basis for system design.Modulated signal generator was designed in the paper and the main work is as follows:(1)Firstly,The paper outlines the development situation and the working principle of the DDS technology,the principle and structure of CORDIC algorithm;Then analyzed the most complex of the two barrel type shift register in the traditional CORDIC algorithm,and using a multiplexer to improvement it;And then analyzed the performance of the two kinds of structure through the list.From the perspective of saving hardware resource,conceiving the algorithm that adjustable duty ratio of square wave and triangle wave to replace the traditional design method of a look up table.(2)The paper introduced the design of the modulated signal generator,according to the related theory,built the simulation model of Sine and Cosine wave in Simulink.After that,treating the Sine and Cosine wave as a reference signal of modulation signal.Then built the simulation model of square wave and triangle wave that the duty cycle adjustable,pseudo random signal,2PSK and AM modulated wave.The simulation verified the correctness and feasibility of the algorithm.The systematic function of DDS was simulated and verified with the Modelsim,and substantialized the design module on FPGA,Finally,using 14 bits'DAC904 for analog-to-digital conversion,after the op-amp OPA690 displayed on the oscilloscope waveform.(3)From the perspective of hardware resources,comparison was made of the hardware costs of DDS system designed with the two methods respectively before and after the improvement.Analysis it is concluded that the improved algorithm has more advantages.Then test found that:?The adoption of improvement algorithm has achieved the functional simulation and output wave of various modules of DDS signal generator,which has verified the validity of module function.?The adoption of CORDIC algorithm has saved hardware resources,and the improved design will save more hardware resources.?The paper will serve as experimental basis for further studies and development the modulated signal in the future.