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I基于DDS的高精度信号发生器的设计摘要频率源是雷达、通信、电子对抗与电子系统实现高性能指标的关键，很多现代电子设备和系统的功能都直接依赖于所用频率源的性能，因此频率源被人们喻为众多电子系统的“心脏”。直接数字频率合成(DDS)是近年来发展起来的一种新的频率合成技术。其主要优点是相对带宽很宽、频率转换时间极短(可小于20ns)、频率分辨率很高、全数字化结构便于集成、输出相位连续、频率、相位和幅度均可实现程控。因此，能够与计算机紧密结合在一起，充分发挥软件的作用。作为应用，现在己有DDS产品用于接收机本振、信号发生器、通信系统、雷达系统、跳频通信系统等。本系统采用AT89C52单片机和AD9851为核心，辅以必要的模拟，数字电路，构成了一个基于DDS技术的信号发生器。该软件系统采用4*4键盘操作，以菜单形式进行显示，操作方便简单，软件增加了许多功能。它通过启动DDS把内存缓存区的数据读出送到DDS后输出相应的频率，并把数据转换为BCD码，通过数码管进行显示。该系统体积小、稳定度、精度极高，方便携带，适用于当代的尖端的通信系统和精密的高精度仪器以及高频无线传输系统等。关键词：信号发生器，DDS,AT89C52，AD9851IIDDS-basedHighPrecisionSignalGereratorABSTRACTThefrequencysourceistheradar,thecorrespondence,theelectroniccountermeasureandtheelectronicsystemrealizationhighperformancetargetkey,theverymanymodernelectronicinstallationandthesystemfunctionalldirectlyreliesoninusesthefrequencysourcetheperformance,thereforethefrequencysourceisexplainedbythepeopleforthemultitudinouselectronicsystem;theheart;.Thedirectdigitalfrequencysynthesizes(DDS)isonekindofnewfrequencysynthesistechnologywhichtherecentyearsdeveloped.ltsmainmeritistherelativebandwidthisverywide,thefrequencyswitchingtimeisextremelyshort(maysmallthan100ns),thefrequencyresolutionisveryhigh,theentiredigitizedstructureisadvantageousfortheintegration,theoutputphasecontinuously,thefrequency,thephaseandthescopemayrealizetheprogramcontrol.Therefore,canunifycloselyinwiththecomputertogether,fullydisplaysthesoftwarethefunction.Astheapplication,hadtheDDSproducttouseinthereceiverlocaloscillation,thesignalgeneratingdevice,thecommunicationssystem,theradarsystem,thefrequency-hoppingcommunicationssystemnowandsoon.ThissystemusestheAT89C52andAD9851areacore,auxiliarybynecessitysimulation,digitalcircuit,constitutedonebasedontheDDStechnologysinewavesignalgeneratingdevice.Thissoftwaresystemusesthe4*4keyboardoperation,carriesonthedemonstrationbythemenuform,theeaseofoperationissimple,thesoftwareincreasedmanyfunctions.ItthroughstartsDDS,afterdeliversthememorybufferareadataread-outDDStooutputthecorrespondingfrequency,andthedataconversionistheBCDcode,carriesonthedemonstrationthroughtheLEDdisplay.Thissystemvolumesmall,thestability,theprecisionareextremelyhigh,facilitatethecarryhome,issuitableincontemporary[onlinetranslation]andsoonacmecommunicationssystemandpreciseprecisioninstrumentaswellashighfrequencywirelesstransmissionsystem.KEYWORDS:SignalGererator，DDS，AT89C52，AD9851III目录摘要...........................................................................................................................................IABSTRACT..............................................................................................................................II目录........................................................................................................................................III1绪论........................................................................................................................................11.1频率合成技术概述......................................................................................................11.2直接数字频率合成技术的应用与现状......................................................................21.3信号发生器概况..........................................................................................................31.3.1信号发生器分类................................................................................................41.3.2各类信号发生器特点........................................................................................41.4系统设计方案..............................................................................................................61.5本文研究的主要内容..................................................................................................71.6本章小节......................................................................................................................72直接数字频率合成................................................................................................................82.1存储器与波形数据......................................................................................................82.2波形发生器的系统组成..............................................................................................82.3采用DDS方式的波形发生器....................................................................................82.3.1相位累加器........................................................................................................92.3.2查询表ROM....................................................................................................102.3.3数模转换器......................................................................................................102.4DDS输出频谱............................................................................................................102.5DDS设计中的参数选择............................................................................................112.6本章小节....................................................................................................................113硬件设计...............................................................