频率合成技术在现代电子技术中具有重要的地位。在通信、雷达和导航等设备中，它可以作为干扰信号发生器；在测试设备中，可作为标准信号源，因此频率合成器被人们称为许多电子系统的“心脏”。直接数字频率合成（DDS——Digital Direct Frequency Synthesis）技术是一种全新的频率合成方法，是频率合成技术的一次革命。本文主要分析了DDS的基本原理及其输出频谱特点，并采用VHDL语言在FPGA上实现。对于DDS的输出频谱，一个较大的缺点是：输出杂散较大。针对这一缺点本文使用了两个方法加以解决。首先是压缩ROM查找表，-Abstract；The frequency synthesis technology has the important status in the modern electronic technology. In equipment such as correspondence, radar and navigation, it may work as the unwanted signal generator　In the test facility, may work as the standard signal source, therefore the frequency synthesizer is called by the people as "the heart" of many electronic systems .DDS——Digital Direct Frequency Synthesis technology is one brand-new frequency synthetic method, is a frequency synthesis technology revolution. This paper　 analyzes the basic principle of DDS and its output frequency spectrum characteristic, and realizes it with VHDL language on FPGA. In regard to the output