Design Of Direct Digital Frequency Synthesizer Based On CORDIC Algorithm

Direct digital frequency synthesis technology has many advantages,such a high frequency resolution,fast conversion speed,continuous phase etc,it is widely used in communication,electronic countermeasures and military fileds.The DDS output signal realized by all-digital structure has a small frequency range and large spurious,which limits the further application of DDS.In order to improve the quality of output signal and achieve various of digital modulation.a DDS signal generator based on CORDIC algorithm is designed and implemented on the development platform of FPGA.The main research contents of this thesis are:(1)CORDIC algorithm optimization.Aiming at the problem that existing in the traditional CORDIC algorithm has a small convergence range and many iterations,expands the convergence range of the algorithm by interval transformation,and reduces the number of iterations of the corresponding angle by de-redundant rotation.The simulation results of Modelsim show that the computational speed of the optimized algorithm optimization algorithm is significantly improved when calculating the corresponding angle.(2)Hardware circuit design of signal generator.In this paper,the signal generator hardware circuit is designed with EP4CE10E22C8 chip as the processing unit,which is mainly divided into core board and digital-to-analog conversion module.The core board includes system power supply circuit,SDRAM interface circuit,reset circuit,etc.the Digital-to-analog conversion module includes DAC interface circuit and amplifier circuit,etc.(3)Logic design of signal generator.The logic design mainly includes the Nios ? soft core processor,and internal data processing modules of FPGA.The Nios ? soft core processor mainly processes the data received by serial port.The internal data processing of the FPGA generates corresponding signals according to the input signal frequency and performs corresponding modulation.In order to control the signal generator flexibly,the upper computer is also designed based on Qt.The test results show that the signal generator can generate 2ASK,2FSK,2PSK and QPSK digital modulation signals and sinusoidal signals,and the waveforms is good.Through the FFT function of the oscilloscope,the frequency spectrum of the signal is tested.The results show that the signal spurs are small and the quality of the signal is better.The DDS signal generator based on CORDIC algorithm has the advantages of continuous output signal waveform,high spectral purity and realization of multiple digital modulations.it has certain practical application value.