摘要直接数字频率合成(DirectDigitalFrequencySynthesis，简称DDS)是从相位概念出发直接合成所需波形的一种新技术，它采用一个恒定的输入参考时钟，通过数据处理的方式产生频率、相位可调的输出信号。直接数字频率合成系统由相位累加器、波形ROM、D/A转换器和低通滤波器构成。它具有频率分辨率高、频率切换速度快、频率切换时相位连续等优点。其产品在成本、性能、功能集成及封装尺寸方面也要优于其它频率合成器。因而，DDS在基于数字信号处理的现代通信频率控制中被广泛应用。本文首先介绍了频率合成器的发展，阐述了基于现场可编程门阵列(FPGA)实现DDS技术的意义；然后介绍了DDS的基本原理、结构及特点，对其频谱和噪声进行了分析；接着对所使用的工具做了介绍；最后是利用FPGA进行DDS的设计。通过使用VHDL和MAX+PLUSⅡ进行编程仿真，实现了DDS的功能，满足了设计要求。利用FPGA器件设计DDS，使电路设计过程得到简化，系统可靠性得以提高，同时FPGA的可编程性为修改、添加和优化DDS提供了方便。关键词：直接数字频率合成；现场可编程门阵列；MAX+PLUSⅡAbstractDirectDigitalFrequencySynthesisisakindofnewtechniqueswhichcansynthesizeanywaveformdirectlydependingontheconceptofphase.Itadoptsdigitaldataprocessingblocksasameanstogenerateafrequencyandphasetunableoutputsignalreferencedtoafixed-frequencyprecisionclocksource.ADDSsystemconsistsofthephaseaccumulators,thesinelook-uptable,thedigitaltoanalogconverter,andthelow-passfilter.Itisofhighfrequencyresolution,fastfrequencyswitchingspeed,theabilitytoswitchfrequencieswhilemaintainingconstantphaseandsoon.Comparedwithotherfrequencysynthesizer,DDSproductsarecost-competitive,high-performance,functionally-integratedandsmallpackage-sized.Therefore,itiswidelyusedinmanyfieldsofmoderncommunicatecontrolbasedonDigitalSignalProcessing.ThedissertationfirstlyintroducesthedevelopmentoffrequencysynthesistechniquesanddiscussesthesignificanceofrealizingthedirectdigitalfrequencytechniquebasedonFieldProgrammableGateArray(FPGA).Secondly,itintroducesthebasicprinciple,structureandthecharacteristicsofDDS.Besides,itanalyzesthespectrumandthesourceofnoiseofDDS.Then,thetoolsusedarereferredto.Finally,FPGAisusedtodesignDDS.ThesimulationresultisgivenbyVHDLandtheMAX+PLUSⅡsoftware,itprovesthatthedesignrealizesthefunctionofDDSandsatisfiestherequirement.TheuseofFPGAdevicesgreatlysimplifiesthecircuitdesignprocessofDDSandimprovesthereliabilityofsystem.Atthesametime,theprogrammedabilityofFPGAprovidesgreatconveniencetomodify,addandoptimizethefunctionsofDDS.Keywords:DirectDigitalFrequencySynthesis;FieldProgrammableGateArra