摘要

本论文设计了一款全数字信号发生器，采用直接数字频率合成（DDS）技术为核心方案。以STC89C52单片机作为系统控制核心，通过控制两路DDS芯片AD9850，产生两路设定频率的正弦波和方波信号。输出信号经过处理后，一路可输入至AD7524程控衰减器，在单片机的控制下完成对信号幅度的程控调整；另一路信号与经过处理的另一路信号一同输入模拟乘法器AD835，一路作为载波，一路作为调制波，实现调幅（AM）功能。同时，将DDS信号输入到CD4046B锁相环芯片可产生调频（FM）信号。

在硬件设计方面，系统力求电路简单，充分利用各芯片功能。软件设计上，发挥编程灵活的特点，挖掘单片机资源以满足设计要求。系统还具备红外遥控控制功能，可接收红外遥控的控制码，并通过LCD12864液晶显示所有数据，实现了友好的人机交互。

经过实际测试，该全数字信号发生器能够输出正弦波和方波，其输出波形的频率范围和幅度范围均达到了设计要求，频率步进值和幅度步进值也符合题目设定。然而，由于设计时间有限，该系统仍存在一些可改进之处，未来可进一步优化硬件电路和软件算法，提高信号发生器的性能和稳定性。

关键词：全数字信号发生器；直接数字频率合成；STC89C52单片机；AD9850芯片；调幅；调频

Abstract

This paper presents the design of a fully digital signal generator, which adopts Direct Digital Frequency Synthesis (DDS) technology as the core solution. The STC89C52 microcontroller serves as the system control core, controlling two DDS chips AD9850 to generate sine and square wave signals with set frequencies. After processing, one part of the output signal can be input to the AD7524 programmable attenuator for amplitude adjustment under the control of the microcontroller. Another part of the signal, along with the processed signal from the other channel, is input to the analog multiplier AD835, with one acting as the carrier wave and the other as the modulating wave, to achieve Amplitude Modulation (AM) function. Meanwhile, inputting the DDS signal to the CD4046B phase-locked loop chip can generate Frequency Modulation (FM) signals.

In terms of hardware design, the system strives for simple circuits and makes full use of the functions of each chip. In software design, the flexibility of programming is exploited, and the resources of the microcontroller are utilized to meet the design requirements. The system also has infrared remote control function, which can receive control codes from an infrared remote control and display all data through the LCD12864 liquid crystal display, achieving friendly human-computer interaction.

After actual testing, the fully digital signal generator can output sine and square waves, and the frequency range and amplitude range of the output waveforms meet the design requirements, as do the frequency step and amplitude step values. However, due to limited design time, there are still some areas for improvement in the system. In the future, the hardware circuit and software algorithm can be further optimized to enhance the performance and stability of the signal generator.

Key Words：fully digital signal generator; Direct Digital Frequency Synthesis; STC89C52 microcontroller; AD9850 chip; Amplitude Modulation; Frequency Modulation