【本科优秀毕业设计】简易调幅发射机

毕业设计论文简易调幅发射机摘要本系统为简易调幅发射机，主要是由调幅信号源、幅度调制模块和高频高效功率放大器组成，本设计中运用了锁相环频率合成和反相功率合成原理。调制信号源部分是由LC振荡电路产生正弦波，锁相环芯片MC145152和双模分频器MC12017组成锁相环路，并且经过环路滤波器，最终将载波频率精确的锁定在15MHZ。调制模块主要是运用模拟乘法器进行调幅，本设计中使用MC1496进行调幅。高频高效功率放大级应用了功率合成技术，采用反相推挽功率合成电路，负载50输出功率大于60MW。本文中首先对调幅发射机的发展情况及面临的问题进行了说明，其次对调幅通信系统原理做了相应的说明，最后对电路进行具体设计。关键词调幅发射机；锁相环；功率合成器ABSTRACTSUMMARYOFTHESYSTEMFORAMTRANSMITTERS,MAINLYFROMTHEAMSIGNALSOURCE,AMPLITUDEMODULATIONMODULEANDHIGHFREQUENCYPOWERAMPLIFIEREFFICIENTCOMPONENTS,THEDESIGNUSEDPLLFREQUENCYSYNTHESIZERANDRPPOWERSYNTHESISTHEORYMODULATIONSIGNALSOURCEPARTBYTHELCOSCILLATORCIRCUITISMYSTERIOUSWAVE,MC145152PLLCHIPDUALFREQUENCYDIVIDERANDMC12017PLLCOMPONENTS,ANDHASGONETHROUGHALOOPFILTER,WHICHWILLULTIMATELYCARRIERFREQUENCYPRECISELOCKIN15MHZMODULATIONMODULEISMAINLYUSEDFORAMANALOGMULTIPLIER,THEDESIGNFORUSEMC1496AMHIGHFREQUENCYPOWERAMPLIFIEREFFICIENTUSEOFPOWERLEVELSYNTHESISTECHNOLOGY,RPPOWERPUSHPULLCIRCUIT,50LOADOUTPUTPOWEROFGREATERTHAN60MWTHISARTICLEFIRSTAMTRANSMITTERTOTHEDEVELOPMENTANDTHEPROBLEMSFACINGTHENOTE,SECOND,COMMUNICATIONSYSTEMSTHEORYAMDONEACORRESPONDINGNOTE,THELASTPAIROFCIRCUITDESIGNKEYWORDSAMPLITUDEMODULATEDTRANSMITTERLOCKAPPEARANCERINGPOWERSYNTHESIZER目录摘要IABSTRACTII第1章绪论111课题背景112本课题发展状况3121课题的国内外发展现状3122研究成果3123发展趋势3124存在的问题4第2章调幅通信系统原理分析521调幅电路的原理522LC振荡电路的原理523锁相环路的组成及工作原理7231环路滤波器的原理8232压控振荡器的原理924锁相环频率合成器原理1025功率放大器的原理1126反相功率合成原理1327本章小结14第3章系统框图与电路设计1531系统框图1532LC振荡电路的设计1533锁相环路的设计17331集成数字锁相环路的设计17332环路滤波器的设计1734调幅调制电路的设计1935高效高频功率放大电路的设计2036本章小结22结论23参考文献25附录127附录233附录337附录455致谢57第1章绪论11课题背景面对各种新的广播制式的竞争，传统的AM广播播处于明显的劣势地位，欧洲许多国家，正逐渐减少中波广播。为了摆脱困境，国外的广播和与其相关的研究机构，努力寻求新的途径，使AM广播获得新生。将现有的AM广播进行数字化改造，是一条必由之路。我国的广播和工业界也逐渐开始关注数字AM，希望能找到一个行之有效的系统，改造我国大量存在的传统AM广播。数字AM是一种新的广播体制，技术还在不断发展，各国都在研究。1998年3月在广州召开了世界数字AM成立大会，经过3年多的努力，2001年国际电信联盟ITU已通过了数字调幅广播的国际标准，这将推动数字调幅广播的进一步广泛应用。世界数字广播公司总裁彼得申格称，数字调幅广播为沉闷的调幅广播市场带来了新鲜空气。国际电联的决定具有划时代的意义，全世界的广播听众将获得价廉物美的高质量数字广播服务，这是半导体发明以来广播事业最大的进步。由于数字AM是在现有的AM波段中进行播出，考虑到现阶段我国的国情，发展数字AM必须考虑以下几方面的问题。根据国内外已公开的研究结果和资料表明，为了不影响现有的模拟AM广播，不变动原有的频率分配，限制数字AM带宽，应保持现有中、短波广播带宽如9KHZ。有限的带宽必然限制了新系统可能达到的声音质量和数据传送能力，应用目前的音频数字压缩技术，9KHZ带宽的数字AM系统质量可达FM水平同时提供1KB/S的数据业务。利用29KHZ的带宽，声音质量可接近CD质量。应利用现有发射设备并保持高效率为了扩大覆盖范围和提高效率，继脉冲宽度调制PDM发射机之后，又出现了脉冲阶梯调制PSM大功率发射机。与国外一样，我国中短波发射台的发射机已经或正在更换为这种新型的发射机。如果未来的数字声音广播系统不再继续使用这些昂贵的大功率、高效率的发射设备，那将造成极大的浪费，是十分可惜的。鉴于此，国外正在试验新的数字传输系统仍然使用现代发射机的调制器和高频前级、末级被调级功率放大器。此外，继续保持这些发射机高的效率是非常重要的。要留住原有的听众群就应有较长的过度期我国有数亿台调幅接收机，如果一个模拟AM电台从某一天起改为数字声音广播运行，那么经常收听该电台广播而没有数字声接收机的听众就不可能再用包络检波的接收机收听该台的广播。考虑到绝大多数听众是在农村和偏远地区，尽快拥有数字声接收机不太现实，为了不失去已有的听众，就需要较长时间的过渡期。在过渡期间内，应做到模拟、数字之间相互无影响，也叫兼容。AM波段的广播，由模拟制向数字制过渡是逐步完成的，就像黑白电视向彩色电视过度一样。采用目前已成熟的技术，在发射机进行固态化改造的同时，采用最先进的数字调幅技术将原有发射机进一步改造成数字调幅发射机，作为数字化进程中的一种阶段性技术加以应用，不时为一个较好的办法。运用数字调幅技术的数字调幅发射机即DAM发射机，它最早是由美国哈里斯HARRIS公司于上世纪80年代后期发明的新式发射机，其发射后的收听效果可接近调频广播的质量。尽管这样改造后的反射机还不是真正意义上的数字AM系统没有数据传送，但比起PDM、PSM发射机的各项指标已经有了很大的进步，经过上述数字化的改造作为过度，可为今后发展和使用真正的数字AM系统，作好技术准备。下面结合我台即将投入使用的DAM数字调幅发射机对DAM数字调幅发射技术应用作一简要介绍。DAM数字调幅发射机取消了传统的高电平音频功率放大器，直接用数字化音频控制信号在射频功率放大器末级实行高电平调幅，它把主振、调制器、和射频功放三合一，是整机性的脉冲阶梯调制，DAM发射机实际上是大功率射频A/D与D/A转换器。DAM数字调幅发射机克服了以往各种模拟调制难于避免的各种非线性失真，有极好的动态响应，各项电声技术指标远优于其它各类模拟调制的广播发射机。另外，我们还可以采用数字调幅广播技术对现有的中短波广播发射机进行改造，充分利用现有设备和现有的中短波频谱资源。DAM数字调幅发射机的工作原理是这样的，音频信号先经数字处理，变换为12比特数字流，并进行编码，用来控制各射频功率放大器的开关。通过接通射频功率放大器的数量多少，来控制发射机输出射频电平。经带通滤波器光滑处理滤除量化台阶和不需要的频谱分量后，就得到通常所说的幅度调制的射频已调波输出，最后经馈线、调配室传送到天线系统发射出去。有限的带宽必然限制了新系统可能达到的声音质量和数据传送能力，应用目前的音频数字压缩技术，9KHZ带宽的数字AM系统质量可达FM水平同时提供1KB/S的数据业务。12本课题发展状况121课题的国内外发展现状现代广播技术由调幅AM广播、调频FM广播、调频立体声广播到目前已经试播的数字音频广播DAB，以及数字多媒体广播DMB。面对各种新的广播制式的竞争，传统的AM广播处于明显的劣势地位，欧洲许多国家，正逐渐减少中波广播。为了摆脱困境，国外的广播和与其相关的研究机构，努力寻求新的途径，使AM广播获得新生。将现有的AM广播进行数字化改造，是一条必由之路。我国的广播和工业界也逐渐开始关注数字AM，希望能找到一个行之有效的系统，改造我国大量存在的传统AM广播。调幅广播正面临着来自电视、互联网、通讯等的巨大挑战。同传统的广播机相比较，数字调幅广播发射机整机的可靠性、稳定性、抗干扰能力有大大的提高，其音色、音质可与调频机相媲美。2122研究成果数字调幅发射机是一种高效率的设备，比目前国内广泛使用的同功率中波机效率高出2030。目前已经开发出10KW、25KW、50KW、100KW等多种规格和数字广播发射机系列产品，全固态中波数字调幅发射机，并且雷达系统中也有着广泛的应用。3123发展趋势数字AM技术和DAM发射机是AM广播今后发展的必由之路，发展新系统我国已明显落后，但在改造旧系统的进程中，我国虽有一批广播发射台的发射机经技术升级改造成全固态的PDM、PSM或DAM等发射机，但仍有数以千计的大小发射台还等待着这一设备更新时代的到来，作为工作在发射台的技术人员，非常有必要经常充电，迅速提高自身的业务能力和技术水平，尽快掌握DAM发射机的工作原理和使用维护技术，以迎接新的挑战。124存在的问题发射设备，尤其是调幅发射机设备的复杂性，直接影响一项新技术、新系统的推广应用。从长远来看，数字调幅广播将会逐步取代模拟调幅广播。但由于数字调幅广播发射机要比模拟调幅广播发射机复杂得多，只有采用高度集成的微电子技术才能实现。并且在大批量生产的情况下，价格才有可能降下来。第2章幅通信系统原理分析21调幅电路的原理调幅就是使载波的振幅随调制信号的变化规律而变化。实现调幅的方法有低电平调幅和高电平调幅，其中低电平调幅包括平方律调幅和斩波调幅，高电平调幅包括集电极调幅和基极调幅。调幅波的特点是载波的振幅受调制信号的控制作周期性的变化。这个变化的周期与调制信号的周期相同，而振幅变化则与调制信号的振幅成正比。为简化分析手续起见，假定调制信号是简谐振荡，其表达式为21TVVCOS如果用它来对载波进行调幅，那么，在理想的情况下，已调TV0COS波的振幅为22TVKATCOS0式中，为比例常数。因此，已调波可以用下式表示AKTVTT023M0S122LC振荡电路的原理成一个振荡器必须具备的条件是有一套振荡回路，包含两个或两个以上储能元件。在这两个元件中，当一个释放能量时，另一个就接收能量。有一个能量来源，可以补充由振荡回路电阻所产生的能量损失。有一个控制设备，可以使电源功率在正确的时刻补充电路的能量损失，以维持等幅振荡。反馈型LC振荡器有许多形式。按照反馈耦合元件可以分成互感耦合振荡器、电感反馈式振荡器与电容反馈式振荡器等。当要求电容三点式振荡电路的振荡频率更高时，则应使电容C1、C2的值较小。由于C1并接在三极管的C、E极之间，C2并接在三极管的B、E极之间，当管子的极间电容随温度等因素的变化而变化时，将对振荡频率产生显著影响，造成振荡频率的不稳定。为了减小极间电容的影响，提高电路频率的稳定性，对电容三点式振荡电路进行适当改进就形成了改进型电容三点式振荡电路，如图21所示。该电路称为串联型电容三点式振荡电路，又称克拉泼振荡电路。图21串联型电容三点式振荡器由图可知，这种电路是在电容三点式振荡电路的电感支路上串进了一个小电容C而构成的C3对交流短路，属共基组态。C1、C2、C及L组成谐振回路，当C2的情形，所以每个M符号都由两个或两个以上比特构成与DCS中这种有限码元集不同，模拟系统的信号波形是无限的。对于采用信道编码纠错编码的系统而言，消息码元序列转变成了信道码元编码码元序列，每个信道码元标识为UI。由于每个消息码元或信道码元由1个或1组比特构成，这样的码元序列也成为比特流BITSTREAM。对于DCS，关键信号处理过程仅包括的格式化、调制、解调/检测和同步。格式化把源信息转换成数字比特，以保证在DCS内信息与信号处理的一致性。脉冲调制方框之前的信息仍是比特流的形式。调制过程将消息码元或信道码元采用信道编码转换成与传输信道特性匹配的波形。脉冲调制是必不可少的步骤，因为要传送每个符号必须先将其二进制数代码转换成基带波形。术语基带是指从直流延伸到某个有限值的信号频谱，这个值通常是小于几MHZ的有限数。脉冲调制方框通常包括使传输带宽最小化的滤波器。当对二进制数符号应用脉冲时，产生的二进制数波形就称为脉冲编码调制波形。PCM波形有几种类型，在电话通信中这些波形常称多址接入格式化信源编码加密信道编码码多路复用带通调制频率扩展多址接入频率扩展带通调制脉冲调制多路复用信道编码加密信源编码格式化为线路码。当脉冲调制用于非二进制符号时，产生的二进制数波形就称为脉冲编码调制波形。每个消息码元或信道码元都转变为基带波形的形式。在任何电子设备中，脉冲调制之前的比特流都用电压电平表示。INTRODUCTIONCOMMUNICATIONWASONEOFTHEFIRSTAPPLICATIONSOFELECTRICALTECHNOLOGYTODAY,INTHEAGEOFFIBEROPTICSANDSATELLITETELEVISION,FACSIMILEMACHINESANDCELLULARTELEPHONES,COMMUNICATIONSYSTEMSREMAINATTHELEADINGEDGEOFELECTRONICSPROBABLYNOOTHERBRANCHOFELECTRONICSHASASPROFOUNDANEFFECTONPEOPLESEVERYDAYLIVES,THERE,WEWILLCONSIDERTHEBASICELEMENTSTHATARECOMMONTOANYSUCHSYSTEMATRANSMITTER,ARECEIVER,ANDACOMMUNICATIONCHANNELFIRSTOFALL,LETUSREVIEWSOMEOFTHEFUNDAMENTALSTHATYOUWELLNEEDFORLATERSTUDYANDINTRODUCEYOUTOSOMEOFTHECIRCUITSTHATARECOMMONLYFOUNDINRADIOFREQUENCYSYSTEMATRANSMITTER,ARECEIVER,ANDACOMMUNICATIONCHANNELWEBEGINWITHANALOGSYSTEMSTHEREADERWHOISIMPATIENTTOGETONTODIGITALSYSTEMSSHOULDREALIZETHATMANYDIGITALSYSTEMSALSOREQUIREANALOGTECHNOLOGYTOFUNCTIONTHEMODERNTECHNOLOGISTNEEDSTOHAVEATLEASTABASICUNDERSTANDINGOFBOTHANALOGANDDIGITALSYSTEMSBEFORESPECIALIZINGINONEORTHEOTHERITISOFTENSAIDTHATWEARELIVINGINTHEINFORMATIONAGECOMMUNICATIONTECHNOLOGYISABSOLUTELYVITALTOTHEGENERATION,STORAGE,ANDTRANSMISSIONOFTHISINFORMATIONELEMENTSOFACOMMUNICATIONSYSTEMANYCOMMUNICATIONSYSTEMMOVESINFORMATIONFROMASOURCETOADESTINATIONTHROUGHACHANNELFIGURE111ILLUSTRATESTHISVERYSIMPLEIDEATHEINFORMATIONFROMTHESOURCEWELLGENERALLYNOTBEINAFORMTHATCANTRAVELTHROUGHTHECHANNEL,SOADEVICECALLEDATRANSMITTERWILLBEEMPLOYEDATONEANDARECEIVERATTHEOTHERTHESOURCETHESOURCEORINFORMATIONSIGNALCANBEANALOGORDIGITALCOMMONEXAMPLESAREANALOGAUDIO,VIDEOSIGNALSANDDIGITALDATASOURCESAREOFTENDESCRIBEDINTERMSOFTHEFREQUENCYRANGETHATTHEYOCCUPYTELEPHONEQUALITYANALOGVOICESIGNALS,FORINSTANCE,CONTAINFREQUENCIESFROM300HZTO3KHZ,WHILEANALOGHIGHFIDELITYMUSICNEEDSAFREQUENCYRANGEOFAPPROXIMATELY20HZTO20KHZVIDEOREQUIRESAMUCHLARGERFREQUENCYRANGETHANAUDIOANANALOGVIDEOSIGNALOFTELEVISIONBROADCASTQUALITYNEEDSAFREQUENCYRANGEFROM6MHZTOABOUT8MHZTVSIGNALSOVERTHEAUDIOSIGNALOFTHENEEDFORHIGHERFREQUENCYRANGEQUALITYOFATELEVISIONVIDEOSIGNALNEEDS68MHZFREQUENCYRANGEDIGITALSIGNALFROMANAUDIOORVIDEOSIGNAL,ORDATACOMPONENTSEG,TEXTFIGURESANDCHARACTERSDIGITALSIGNALFROMARBITRARYBANDWIDTH,THISDEPENDSONTHE489,000BITSANDTHENUMBEROFBINARY1AND0SIGNALCONVERSIONMETHODTHECHANNELCOMMUNICATIONCHANNELCANBEANYMEDIUMACONDUCTOR,AFIBEROROURFREEDOMTOLIVEINSPACESOMETIMESCHANNELDIRECTBEARINGINFORMATIONFOREXAMPLE,THESPEECHSIGNALDIRECTLYFROMONEPAIROFUNSHIELDEDTWISTEDPAIRTELEPHONECABLECARRYINGMOREOVER,THELIBERALSPACEWIRELESSLINKCOULDBEUSEDDIRECTLYFORCARRYINGVOICESIGNALS,WHICHNEEDTOUSEACARRIERSIGNAL,ITCANMAKETHEVOICEFREQUENCYSIGNALSTHROUGHTHECHANNELTUNNELORDISSEMINATIONINFORMATIONFROMTHECARRIERSIGNALCHANGEORMODULATION,SUCHINFORMATIONCANBEATTHERECEIVINGENDWASRESTOREDWHENUSINGCARRIER,THEINFORMATIONSIGNALISCALLEDMODULATIONSIGNALASTHECARRIERFREQUENCYINFORMATIONTHANTHEHIGHFREQUENCYSIGNAL,THEINFORMATIONSIGNALSPECTRUMOFTENCALLEDBASEBANDSIGNALS,SOTHATINFORMATIONSIGNALMODULATIONSIGNALANDBASEBANDSIGNALWHICHHASTHREETERMSINTHEMODULATEDCARRIERCOMMUNICATIONSPROGRAMSSIGNIFICANCEISTHESAME图111TYPESOFMODULATIONALLMODULATIONSYSTEMLITTLEDIFFERENT,THECARRIERFREQUENCYTHANTHEHIGHESTBASEBANDHIGHFREQUENCYNORMALLY,CARRIERWAVEISBEINGMYSTERIOUSTHEBASEBANDSIGNALISOFTENINSTANTANEOUSRATEOFCHANGEOFCARRIERPARAMETERSCARRIERISMYSTERIOUSTOTHEGENERALEXPRESSIONCETESINWHEREETINSTANTANEOUSVOLTAGEASAFUNCTIONOFTIMEECPEAKVOLTAGEFREQUENCYINRADIANSPERSECONDCTTIMEINSECONDSPHASEANGLEINRADIANSMODULATIONUSEDINMATHEMATICSUNITSRADIANSPERSECOND,ENABLINGTHEEQUATIONISSIMPLEOFCOURSE,INDISCUSSINGTHEACTUALDEVICE,COMMONLYUSEDFREQUENCYHERTZSAID,ANDNOTRADIANSPERSECOND,USINGEXCHANGEBASICTHEORY,BETWEENTHETWOVERYEASILYCONVERTEDMODULATIONCANCHANGETHEPARAMETERSOFMAGNITUDE,FREQUENCYANDPHASECOMPOSITEMODULATIONISPOSSIBLEFOREXAMPLE,THISDIGITALINFORMATIONUSINGTHECIRCUITTHATISALSOAVAILABLEAMPLITUDEMODULATIONPHASESMODULATIONTHESIGNALTRANSMITTERMODULATIONCOMPLETED,THERECEIVERUSINGAPROCESSKNOWNASCONTRARYDEMODULATIONORDETECTION,TORESTORETHEORIGINALBASEBANDSIGNALSSIGNALBANDWIDTHNOTAMYSTERIOUSMODULATIONISASINGLECARRIERWAVEFREQUENCYFORM,ITONLYOCCUPIES0BANDWIDTHANDTHEMODULATEDSIGNALISNOLONGERASINGLEFREQUENCYWAVESAREMYSTERIOUS,ITWILLTAKEUPALOTOFBANDWIDTHSPECIFICALLY,HOWMUCHBANDWIDTHOCCUPIED,ITDEPENDSONTHEBASEBANDSIGNALFREQUENCYRANGEORDIGITALCOMMUNICATIONOFTHEDATARATEANDTHEUSEOFTHEMODULATIONKAZAKHSTANSTERILEISRELATEDTOTHELAWOFBANDWIDTHANDINFORMATIONOFATOTALCAPACITYOFTHERULES,ITSHOWSINAGIVENTIMETRANSMISSIONISPROPORTIONALTOTHEAMOUNTOFINFORMATIONGIVENMODULATIONBANDWIDTHTKBIWHEREIAMOUNTOFINFORMATIONTOBESENTKACONSTANTTHATDEPENDSONTHETYPEOFMODULATIONBCHANNELBANDWIDTHTTIMEAVAILABLESOMEUSEDTHEMODULATION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