摘 要
本文论述了直接数字频率合成技术(DDS)的信号发生器的设计与实现。本设计以DDS芯片AD9850为频率合成器，以AVR单片机ATmega16为进程控制和任务调度核心，用AD603实现增益控制（AGC）和功率放大，串行数模转换器(D/A)MAX531实现方波占空比调节，并用LCD12864液晶显示及键盘构成幅度、频率、方波占空比均可调的函数信号发生器。
在对AD9850频率控制字及参数的计算、增益控制、方波占空比调节、两相正弦波相位差调节、LCD显示原理、底层驱动程序等简要讨论的基础上进行了研究，提出了该设计中所涉及到的问题以及解决方案，该信号发生器输出正弦波信号频率范围为1Hz~12MHz，方波信号频率范围为500Hz~500KHz；步进1Hz，10Hz，100Hz，lkHz，10kHz,100kHz，1MHz可键盘选取；正弦波的电压峰峰值可以在1~5V范围内步进调节，幅度调节精度达0.1V；方波占空比从10％～90％可任意设定；此外，该信号发生器能同时产生两相正弦波，相位差可以是0°，45°，90°。测试表明，该DDS信号发生器具有工作稳定、精度高、失真度小、频率范围大、步进选择多、控制灵活的优点，具有广泛的实际应用前景。
关键词：DDS芯片AD9850 AVR单片机 幅度调节 占空比调节
Abstract
This article elaborated the signal generating device design and the realization of the Direct Digital Frequency Synthesis Technology (short for DDS). The design regards DDS chip AD9850 as frequency synthesizer, with AVR Microcontroller (MCU) ATmega16 for the processing control and task scheduling, and with AD603 to realize the gain control and power amplification (AGC), and with serial DAC (D/A) MAX531 to come to square-wave duty cycle regulation, then using LCD12864 liquid crystal display and keyboard to composite the function signal generation with adjusted amplitude, frequency, duty cycle wave.
I would like to propose the involving issues and resolving proposals on the basis of simply researching of words and parameters counted with AD9850 control, gain control and duty cycle wave regulation, two phase sine wave phase difference adjustment, LCD displaying principle, low-level drivers. The sine wave signal rate outputting from signal generator is 1 Hz~2 MHz: square signal rate is 500Hz~500KHz; the step-by-step can be choose from keyboard by 1Hz, 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, 1MHz; sine wave voltage peak can be adjusted ranging from 1 to 5V by step, amplitude modulation reaches 0.1V; duty cycle wave can be enacted arbitrarily; besides, the signal generator can create two sine wave at the same time, and the difference can be 0°,45°,90°. It shows that DDS signal generator gets the virtues of stable working, high accuracy, small distortion, large frequency range, multi-step selection, flexible control, owning a wide prospect of practical application.
Key words: DDS chip AD9850 AVR MCU amplitude regulation duty cycle wave