摘要频率合成器是现代电子系统的重要组成部分，是决定电子系统性能的关键设备之一。本文首先介绍了频率合成的概念、发展以及直接数字频率合成技术(DDS)的现状和发展趋势。分析了DDS的工作原理及其基本结构，然后根据系统指标合理地采用了DDS技术，以AD9851芯片为核心、AT89C51单片机为控制核心，设计了一种结构简单性能优良的信号发生器。详细分析了该信号发生器的系统结构、软硬件设计和具体电路实现。信号发生器的硬件部分包括三个模块，分别是信号产生控制模块、人机交互模块和信号处理模块。软件部分是在Keil的开发环境下，以Proteus为仿真平台，主要开发基于单片机AT89C51的数据处理和控制程序。最后针对课题对频率源合成性能的要求，对相位噪声的抑制和杂散性能的优化进行了深入的分析，并对比实际电路提出了设计的改进建议和方案。64580

毕业论文关键词  信号发生器；DDS；AD9851；频率合成；

毕业设计说明书（论文）外文摘要

Title    Design of the direct frequency synthesizer based on the control of SCM.                                                              

Abstract Frequency synthesizer is one of the most significant parts used in modern communication and electronic systems．This paper firstly introduces the concept and development of frequency synthesis，as well as the present situation and the trend of development of the direct digital frequency synthesis technology(DDS)．It has analyzed the principle and the basic structure of DDS，then according to the target system，a signal generator with the brief structure and excellent performance is designed with adopting DDS technology，which is based on the AD company`s DDS chir-AD9851 and controlled by SCM．The system structure，the design of software and hardware and the way to realize the circuitry of the signal generator is analyzed in detail．The hardware of the signal generator consists of three blocks，those are signal generate module、keyboard and LCD display module、signal processing module．Software of the system mainly focuses on the design of C51 including control、data processing、communication  with Keil as the integrated development environment and Proteus as the simulation environment. The noise inversion and optimization of spurious suppression characteristic are analyzed in depth according to requirement of the synthetic performance．At last, this paper proposes improvement program by comparing the actual circuits．

Keywords  signal generator；DDS；AD9851;frequency synthesis.

1 绪论 1

1.1 课题来源 1

1.2 课题背景 1

1.3 直接频率合成技术现状 1

1.4 本文的简单介绍 2

2 系统总体方案的分析与设计 3

2.1 DDS的基本原理 3

2.2 DDS的工作特点 5

2.3 系统设计原理 5

2.4 系统设计者设计要求 6

2.5 系统框图分析和设计 6

3 系统硬件设计 7

3.1稳压电源设计 8

3.2 DDS芯片的选择与单片机之间的通信 10