Low Spurious Components Wideband DDS Technologies Research

Direct digital frequency synthesis (DDS) is a new generation frequency synthesistechnology,with fast conversion speed and high frequency resolution, low phase noise,frequency agile, continuous phase, etc. Modern radar and communication systems haveraised extremely demanding requirements for the synthesized frequency hopping time,bandwidth and noise levels. Be treated as the main development direction, direct digitalfrequency synthesis (DDS) has an absolute advantage in terms of frequency switching time.However, its spurious performance in the wideband spectral range is far below the systemrequirements, which has seriously hampered the development and application of DDStechnology. DDS output frequency is low, spurious performance is not ideal that limit theapplication of DDS. This paper analyze the causes of DDS spurious, propose a method toimprove the performance of DDS spurious, study of the FPGA-based low-noise high-speedDDS technology, and validate actual application. Base on this fundamental phenomena, thisresearch proposes to involve high order sigma-delta modualtiong for the conventional DDSphase accumulator, to set up a comprehensive DDS phase noise and spur level model. Theselection method of various structure and order of sigma-delta modalators, the combinationof multiple and differential modulation structure of sub-band output algorithms, weightsoptimization algorithm are proposed simultaneously. Digital pre-distortion compensationapproach is utilized to further suppress the spurious component at a series of dedicatedfrequencies. The proposed off-line processed phase accumulation method is able to achievehigh-speed DDS, carrying algorithm research, and increasing the output frequency.Combined with a variety of noise reduction algorithms and implementation of innovativeintegrated broadband, agile, low-noise direct digital frequency synthesizer.