湖 北 民 族 学 院
毕业论文（设计）
简易频率特性测试仪
学生姓名： 学 号：
系 别：信息工程学院 专 业： 电子信息 指导教师： 评阅教师：
论文答辩日期 答辩委员会主席
摘 要
频率特性测试仪作为一种测量传输系统幅频特性和相频特性的定量测量仪器，在工程实践和实验室里都有非常广泛的应用。近年来，随着数字电路技术的不断发展，新型的数字式频率特性测试仪已经逐步取代了传统的模拟式频率特性测试仪，精度越来越高，功能也越来越丰富。然而，这些仪器都存在着体积笨重，携带不方便、成本较高的问题。因此，研究设计一款便携式频率特性测试仪有着重要的意义。
本课题主要是研究一种基于零中频解调原理，并用SOPC技术作为控制系统的便携式频率特性测试仪。论文研制基于零中频解调原理的频率特性测试仪，重点研究零中频解调原理的实现以及基于DDS芯片的扫频信号源的电路设计，并采用SOPC技术完成数据的计算以及人际交互界面的设计。
零中频解调电路采用高速乘法器AD835作为乘法运算的核心器件，辅以二阶有源低通滤波器实现对乘法输出结果中直流分量的提取。最后采用TLV2544型12位高速模数转换器实现模拟信号的采集，并通过NIOS II处理器进行软件运算，最终得出被测系统的频率特性。系统采用高性能DDS芯片AD9854作为扫频信号源核心元件，实现了1MHz至40MHz内稳定的正交信号输出，从而保证了系统测量的精度。实测系统能够对谐振点在1MHz至40MHz之间的RLC谐振网络频率特性曲线进行较高精度的测量。
关键字： 零中频解调，AD9854，频率特性，SOPC，NIOS_II
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Abstract
Frequency characteristic test instrument, as a kind of quantitative measuring
instrument that measures transmission system amplitude frequency characteristics and phase frequency characteristics, has been applicated in engineering practice and in the lab very extensively . In recent years, with the continuous development of the digital circuit technology, the new type of digital frequency characteristic tester of which the precision is higher and higher, the function is richer , has gradually replaced the traditional analog frequency characteristic tester . These instruments, however, have problem of heavy volume, inconvenience to carry and the high cost . So the design of a portable frequency characteristic test instrument is of great significance.
This topic mainly studies a portable frequency characteristic tester which is based on the zero intermediate frequency demodulation principle and use OPC technology as a control system .
Thesis develops the frequency characteristic test instrument which is based on zero intermediate frequency demodulation principle .And thesis focuses on the realization of zero intermediate frequency demodulation principle and circuit design of the frequency sweep signal source based on DDS chip , and then completes data
calculation and interpersonal interaction interface design by using SOPC technology . Zero intermediate frequency demodulation circuit adopts high speed multiplier AD835 as the core device of a multiplication operation, supplemented by
second-order active low-pass filter to extract dc component from the output of multiplication. Finally , Zero intermediate frequency demodulation circuit adopts TLV2544 type 12 high-speed analog-to-digital converter to realize the collection of analog signals, and calculates with the NIOS II processor to obtain the frequency
features of the system under test. System adopts high performance DDS chip AD9854 as frequency sweep signal source core components, realize the stable orthogonal signal output within 1 MHZ to 40 MHZ to ensure the measuring precision of the system. Measurement system can conduct a high accurate measure about RLC resonant network frequency characteristic curve of which the resonance point is between 1 MHZ to 40 MHZ .
Key words: zero intermediate frequency demodulation, AD9854, FPGA, NIOS_II, frequency characteristics
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目 录
摘 要 ................................................... I Abstract ...................................................................................................... II
1 绪论
1.1 课题的研究背景、目的及意义 ..................................... 1 1.2 频率特性测试仪的现状 ........................................... 1 1.3 国内外概况 ..................................................... 2 1.4 课题研究内容与组织结构安排 ..................................... 2 1.5 本章小结 ....................................................... 3 2 系统设计方案的研究
2.1 系统的控制特点与性能要求 ....................................... 4 2.1.1 系统的控制特点 ............................................... 4 2.1.2 系统的性能要求 ............................................... 4 2.2 系统实现的几种具体方法和电路分析 ............................... 5 2.2.1 扫描信号源的实现方法分析 ..................................... 5 2.2.2 幅度检测电路实现方法的分析 ................................... 6 2.2.3 相位检测电路实现方法的分析 ................................... 7 2.2.4 零中频解调电路原理分析 ....................................... 8 2.3 本章小结 ...................................................... 10 3 零中频解调电路的设计与实现
3.1 零中频解调电路设计方案论证 .................................... 11 3.1.1 模拟方式与数字方式性能比较 .................................. 11 3.1.2 模拟方式与数字方式成本比较 .................................. 11 3.2 零中频解调电路设计方案及实现 .................................. 12 3.2.1 实现零中频解调电路的元器件选择 .............................. 12 3.2.2 AD835介绍以及特性分析 ...................................... 13 3.2.3 AD835为核心的零中频解调电路设计 ............................ 13 3.2.4 信号放大电路设计 ............................................ 16 3.3 本章小结 ...................................................... 18
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4 扫频信号发生电路的设计与实现
4.1 扫频信号发生电路设计方案介绍 .................................. 19 4.2 扫频信号发生电路硬件电路设计 .................................. 19 4.2.1 AD9854核心电路硬件设计 ..................................... 19 4.2.2 AD9854输出信号滤波网络及放大电路设计 ....................... 22 4.3 本章小结 ...................................................... 23 5 控制系统的设计与实现
5.1 控制系统可选方案分析 .......................................... 24 5.1.1 高性能单片机控制方案介绍 .................................... 24 5.1.2 DSP控制方案介绍 ............................................ 24 5.1.3 FPGA和SOPC控制方案介绍 .................................. 25 5.2 控制系统功能介绍 .............................................. 25 5.2.1 系统人机交互设计 ............................................ 25 5.2.2 模数转换电路设计 ............................................ 26 5.3 控制系统结构设计 .............................................. 27 5.3.1 红外解码电路设计 ............................................ 27 5.3.2 TLV2544型ADC驱动模块设计 ................................ 28 5.3.3 相位、幅度运算模块的设计 .................................... 28 5.3.4 扫频信号源控制模块的实现 .................................... 29 5.4 本章小结 ...................................................... 30 6 系统工作电源设计与实现
6.1 系统电源需求分析 .............................................. 31 6.2 系统电源电路设计 .............................................. 32 6.3 稳压电路设计 .................................................. 32 6.4 本章小结 ...................................................... 33 7 系统软件设计与实现
7.1 系统软件设计需求分析 .......................................... 34 7.2 软件架构设计 .................................................. 34 7.2.1 软件主体设计 ................................................ 34 7.2.2 点频测量原理及软件设计 ...................................... 35
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