基于AD9851的便携式数字扫频仪器的设计(硬件设计)DesignofportabledigitalbasedonAD9851sweepfrequencyinstrument(hardwaredesign)PAGEIIPAGEI摘要扫频仪是测量网络传输特性的仪器，在现代电子测量中占据着重要的地位。本文着重分析了扫频仪的工作原理，提出了一种基于DDS技术的扫频仪的设计方案。在对市场上扫频仪的研究现状和对系统特性进行分析以后，确定了本设计的性能指标和总体方案。此设计主要有扫频信号发生器电路、增益控制电路、自动电平控制电路、检波头输出电路、单片机ATmega128以及电源模块电路等模块组成，其中扫频信号发生器电路采用DDS纯数字化方法，具有高速的频率转换时间、极高的频率分辨率和较低的相位噪声还具有可编程控制等优点，再加上增益控制电路、自动电平控制电路等，使扫频仪能适应各种测试要求。利用微处理器ATmega128作为控制及处理单元，使用集成化的幅度和相位检测芯片，配有LCD192X64液晶显示，使这种扫频仪设计简单，调试方便，性能稳定可靠，系统界面友好，能够在全频范围内自动步进测量，可预置测量范围及步进频率值,可以更加细致的观察频率特性图，给使用者带来方便。关键词扫频仪DDS技术增益控制AbstractSweepgeneratorisaninstrumentformeasuringtransmissioncharacteristicsofthenetwork.Inthispaper,theworkingprincipleofsweepgeneratorwereanalysedemphatically,thenadesignschemebasedonDDStechnologywereputforward.Afteranalysingtheresearchstatusofthesweepgeneratorsinthemarketandthesystemcharacteristics,wemakesuretheperformanceindexandgeneralscheme.Inthisdesign,thesweepgeneratorconsistsofseveralparts,theyrespectivelyaresweptsignalgeneratorcircuit,gaincontrolcircuit,automaticvoltagecontrolcircuit，detectingheadoutputcircuit，atmega128microcontroller,powermodulecircuitInwhichsweptsignalgeneratoradoptthepuredigitaltechniquewhichhashigh-speedfrequencyconversiontime,extremelyhighfrequencyresolution,lowerphasenoiseandtheoutstandingadvantageofprogramecontrol,superaddthegaincontrolcircuitandAutomaticvoltagecontrolcircuit,thesweepgeneratorcanadapttovarioustestrequirements.EmbeddedmicroprocessorAD9851wereusedasthecontrolandprocessingandthecompositivemagnitudeandphasedetectingcircuitLCD192X64makethedesignofsweepgeneratormoresimple,thedebuggingmoreconvenientandtheperformancemorestableandreliable.Inaddition,thissweepgeneratorcanmakesteppingmeasurementautomaticallyinthewholefrequencyrange.Wecanpresetmeasuringrangeandsteppingfrequency,sothedetailedfrequencycharacteristiccurvescanbeseenclearly.Thisfunctionbringsusersmuchconvenience.Keywords:sweepgeneratorDDStechonologygaincontrol