摘 要
采取DDS（直接数字频率合成器）芯片来实现各种信号的输出，并且完成调频和调幅的功能。采用了AD9850芯片（美国模拟器件公司的芯片），用51单片机对AD9850芯片进行控制，而控制单片机采用的是上位机进行的，首先上位机发送数据给51单片机，51单片机再发送信号控制字给DDS芯片，然后DDS芯片的输出所需波形，经由低通滤波获得所需要的信号，接下来是对该信号进行调频调幅。通过在软件中修改DDS芯片的相位控制字，频率控制字等就可以实现对频率的调整，DDS输出正弦信号之后外加一调幅器则可以实现对幅度的调整。调幅是将RC振荡器提供1KHz振荡作为调幅信号，DDS输出作为载波信号，利用乘法器MC1496完成对信号调制。此系统输出的稳定度以及精度都是极高的，特别适用于现在精密度高的仪器与高端的通信系统。
本次论文讲解了DDS（直接数字频率合成器）的原理，描述了这次系统的设计方案，以及系统软件编写以及硬件电路等，其中对调幅模块电路设计与AD9850芯片等都作了详细介绍。
关键词：AT89C51单片机；调幅；AD9850；DDS（直接数字频率合成器）
Abstract
This article mainly introduced uses the direct digital frequency to synthesize the DDS chip to realize the sine signal output, and completes the frequency modulation, the amplitude modulation function. It uses the American simulation component company (AD Corporation) chip AD9850, and with the AT89C51 monolithic integrated circuit to its control, first from the DDS chip output, obtains the sine signal after the low pass filter, then carries on the frequency modulation to this signal, the amplitude modulation. Frequency modulation partial may through revise the DDS chip in software the frequency control word, the phase control word and so on realizes, but the amplitude modulation are partial must after the DDS output sine signal sur- amplitude modulator realization. The amplitude modulation partially the DDS output took the intelligence signal, the RC oscillator provides the 1KHz vibration to take the amplititude-modulated signal, it used multiplier MC1496 to complete to the sine signal modulation. This system output stability, the precision are extremely high, is suitable for the contemporary acme communications system and the precise precision instrument.
This article first introduced the direct digital synthesis principle, then proposed the system system design plan, but also has the system hardware electric circuit and the software compilation design and so on, like uses the AD9851 chip and the amplitude modulation module circuit design has made the detailed introduction.
Key word: Direct digital frequency synthesis (DDS)； AD9850； frequency modulation；amplitude modulation
目 录
引言 ...................................................................................................................... 0 1直接数字频率合成器原理与性能综述 .......................................................... 0 1-1 DDS原理 .......................................................................................................... 0 1-2 DDS性能 .......................................................................................................... 4 2 课题方案设计及论证 .................................................................................... 5 2-1 设计任务及初步规划设计 ................................................................................. 5 2-2 方案提出及系统整体设计框图 .......................................................................... 6 2-2-1 系统各部分设计方案 ..................................................................................... 6 2-2-2 系统整体设计框图 ........................................................................................ 7 3 硬件电路设计 ................................................................................................ 7 3-1 直接数字频率合成模块 ..................................................................................... 7 3-1-1 AD9850内部结构 ........................................................................................... 7 3-1-2 AD9850芯片引脚分布及功能介绍 .................................................................. 9 3-2 单片机控制电路设计 ...................................................................................... 12 3-3 调幅模块设计 ................................................................................................ 13 3-3-1 MC1496内部结构 ......................................................................................... 13 3-3-2 MC1496静态工作点的设置 ........................................................................... 14 3-3-3 MC1496在振幅调制中的应用 ....................................................................... 15 3-4 键盘与显示模块设计 ...................................................................................... 17 4 软件设计 ...................................................................................................... 19 4-1 软件实现思想 ................................................................................................ 19 4-2 软件流程图及程序 ......................................................................................... 19 5 系统调试 ...................................................................................................... 28 5-1 硬件电路调试 ................................................................................................ 28 5-1-1 调试与测试所用仪器 ................................................................................... 28 5-1-2 调试过程 .................................................................................................... 28 5-1-3 调试经验总结 ............................................................................................. 28 5-2 软件调试 ....................................................................................................... 29 5-3 总调试 ........................................................................................................... 29 6 结论 .............................................................................................................. 30 谢 辞 ................................................................................................................ 31 参考文献 ............................................................................................................ 32 附 录 ................................................................................................................ 33