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摘要现代电子技术的发展对电子设备关键器件频率合成器提出了越来越高的要求，对频率合成器的频谱纯度，相位噪声调频速度等指标的要求在不断提高。
本文介绍了直接数字频率合成器的基本结构，工作原理，杂散来源和输出频谱特性;讨论了锁相环的基本结构，相位模型，频率响应，噪声和杂散性能;利用DDS分辨率高和频率转换时间段，以及PLL 对杂散的抑制能力较强的特点，讲DDS与PLL进行组合，实现该两种技术的优势互补。
采用DDS+PLL+倍频的技术将DDS超高频率分辨率，极高的频率准确度和容易实现程控等优点与锁相环良好的窄带跟踪滤波特性相结合，研制了频谱纯净的X波段频率合成器。该频率合成器采用单片机控制DDS和PLL，通过DDS激励PLL实现C波段的频率输出，经过二倍频得到X波段的输出频率。根据系统要求，选择了合适的器件来搭建电路，进行了合理的电路布局和电磁兼容设计。通过实际测试，获得系统的相位噪声。最后对结果进行讨论，分析了存在的问题，并且提出了解决的方法。64455
毕业论文关键词 直接数字频率合成器 锁相环 X波段 相位噪声
毕业设计说明书（论文）外文摘要
Title X-band frequency synthesizer of broadband
Abstract
The fantastic development of the electronic technology is bringing forward higher request for frequency synthesizer.All frequency synthesizers with highly pure spectrum, low phase noise and fast frequency switching speed have dominated development direction of the frequency synthesis technology.According to different application fields.
The hybrid frequency synthesis technology called " DDS+PLL+frequency doubling" used in the subject has many advantages.Using this method,the merits of DDS such as super fine frequency resolution，high frequency accuracy and easy programmed can be in combination with excellent character of narrow-band tracing filter merits of PLL. Thereby，pure spectrum character of the frequency synthesizer in X-band can be realized. By adopting the hybrid DDS+PLL frequency synthetic technology controlled by MCU, the C-band frequency synthesizer has been devised.Then a frequency doubller make the output frequency expand to X-band.T According to the requirement of system,devices suitable to put up the circuit are chosed, carrying on the rational circuit overall arrangement and design of EMC. Phase noise result and picture of spectrum with spur are presented.Finally, analysis of the result is given, and the existing problem as well as methods to resolve it are motioned.
Keywords DDS，Phase Locked Loop(PLL)，X-band，Phase noise.
目次
1 绪论 1
1.1选题背景及意义 1
1.2频率合成技术现状与未来 2
1.3本文的主要内容 3
1.4总结 4
2频率合成器的基本知识 6
2.1频率合成器的简介 6
2.2频率合成器及其技术指标 6
2.3锁相环频率合成器 7
2.3.1锁相环频率合成器工作原理 7
2.3.2基本环路方程 8
2.3.3环路相位模型和基本方程 11
2.3.4 锁相环路的线性分析 12
2.4本章小结 13
3相位噪声的分析