Direct Digital Frequency Synthesizer Technology, Linear Sweep The Research And Application

DDS (Direct Digital Synthesis), as a new generation of Frequency synthesis technology, develops quickly. DDS has many particular advantages, so it is widely used in military affairs and civilian fields. For instance, DDS is widely used in the modern radar fields, communication fields, electronical counterwork fields, and instrument fields, etc. DDS has larger and larger market and application foreground nowadays, so researching on DDS is extremely significant and important.In modern radar fields, the requirements of distance precision and differentiation are increasing, so the requirements of bandwidth and timewidth of LFM signal are increasing too. Traditional analog ways of generating LFM signal, such as sawtooth wave voltage controlled VCO and SAWD optical dispersion delay line, cannot satisfy the requirements of high precision and big product of bandwidth and timewidth. Therefore, it is an important task to generate wide-band and high linearity LFM signal. The way using DDS to generate high linearity LFM signal, and using frequency convert and frequency multiple to get wide-band, is increasingly admired and gradually widely used.At first, this thesis elaborates the importance of modern frequency synthesizer techniques used in modern electronic systems, introduces the basic principles of several kinds of frequency synthesizers and compares their performances, summarizes the trends of modern frequency synthesizer techniques to serialization, miniaturization, modularization and engineering practicability, and especially stresses the development and progress of DDS. Then, this thesis introduces the basic working principle and characteristics of DDS, points out the advantage and disadvantage of DDS, and analyze the sources of spurious signals and the ways to improve the performance of DDS. In addition, according to the analysis of linearity of LFM and the comparition of DDS of ADI, the thesis gives some principles and ways to choose DDS. Through the analysis and comparison among each realization methods and performance of frequency synthesizers, we finally choose DDS+PLL scheme to achieve the tasks. DDS+PLL scheme can make full use of the characteristics of DDS, such as high resolution, fast frequency switching speed, and the characteristics of PLL, such as large bandwidth, good quality of frequency spectrum. Thus, we effectively get high linearity signal using DDS, extend the signal band wide using PLL, and finally achieve the wide-band LFM signal.In the realization process, we choose AD9958 and ADF4106 made by AD Corporation in the USA, design the specific circuit, draw the layout, and finely debug the system. The test results show that the linearity of LFM signal, frequency switching speed, phase noise, and spurious level all meet the requirement of the designed system well. At last, we introduce the problems in the circuit design and give some suggestion of improving the performance of the system.