模拟电视发射机适应数字电视地面传输的技术研究

【作者】 高原；

【导师】 张有志；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 随着广播电视数字化、网络化和信息化技术的迅猛发展,数字电视地面广播将引起广播电视发射技术的一次重大变革。目前,在我国众多发射台站配备了各种型号的模拟电视发射机,随着数字电视地面广播时代的到来,不可能也不允许全面淘汰现有机型,况且模拟电视向数字电视过渡必然要经过数字与模拟共播的过程,因此对现有模拟电视发射机适应数字电视地面传输的技术研究具有重要的意义。 本文首先简述了已为国际电信联盟(ITU)所接纳的三套数字电视地面广播传输标准(分别为美国ATSC标准、欧洲DVB-T标准和日本ISDB-T标准),介绍了我国数字电视地面广播标准的研究现状和国内外数字电视发射机的发展概况。 接下来文章结合数字电视地面多载波传输方案,较为详细的分析了数字电视多载波传输的技术特点,对正交频分复用技术(OFDM)的原理以及OFDM信号的时域特点和频域特性进行了理论分析,阐述了数字电视信号对电视发射机的射频频谱、互调失真、放大通道、频率稳定度和输出滤波器等方面的要求,论证了数字电视OFDM调制方式对电视发射机射频通道的技术要求。 然后以具体机型(法国THOMCAST E UHF系列全固态电视发射机)的模拟电视发射机为例,讨论了发射机功率放大模块的电路组成及功率合成的实现方式,分析了其功率放大通道的特性,并通过对该功率放大器的数学建模,利用非线性随机过程的理论,分析了功率放大器的非线性特性,发现了影响输出端高阶互调失真的主要原因,找到了为适应数字电视的地面传输,如何对模拟电视发射机进行改造的关键技术途径。 在此基础上,论文还对电视发射机功率放大器线性化的几种技术进行了较为详细的分析与比较,重点讨论了功率回退法、负反馈校正技术、前馈校正技术和基于双查表法的数字自适应预失真方案,并结合电视发射机末级功放的特性,指出了各种校正方案的技术可行性和工程实现的局限性。 根据上述分析与研究结果,论文提出了一种模拟电视发射机末级功率放大器数字自适应预失真校正的方案—复数增益表数字基带自适应预失真校正更多还原

【Abstract】 With the rapid development of digital television broadcast toward network and information, DTTB (digital television terrestrial broadcast) will lead a revolution of broadcast technology. At the present, there are various analog television transmitters in different transmission stations in our country, along with the coming of DTTB times, it is unpractical to change all of those transmitters, and the transmission of analog to digital television must come through the process of coexist, so it is significant for the technical analysis of analog television transmitter for digital television terrestrial transmission.In the first chapter, a brief explanation of three DTTB transmission standards: (ATSC of American, DVB-T of Europe, ISDB-T of Japan) adopted by the International Telecommunication Unit is given, and DTTB transmission standard research in our country is introduced. This chapter also gives introduction of digital television transmitter development both in domestic and abroad.The second chapter gives detailed analysis of digital television multi-carrier wave transmission, according to digital television terrestrial transmission scheme, and the theoretical analysis for the property of time domain and frequency domain of orthogonal frequency division multiplexing (OFDM) signal is given. In study with the characteristic of OFDM, this chapter points out the requirement of digital television signal on television transmitter, including radio frequency(RF) spectrum, intermodulation distortion (IMD),amplification channel、 the stability of frequency and the output filter. By theoretical analysis this chapter proves and reviews the special technical requirement of OFDM modulation for analog television transmitter RF channel.In the third chapter, the peculiarity of television transmitter power amplification channel is analyzed according with the concrete analog television transmitter model (France THOMCAST E UHF 10000DD), the composition of the module’s circuit and the power combination mechanism are thoroughly studied. By mathematics models of the power amplifier and the OFDM signal as asequence of random process. Using nonlinear random process analysis, this chapter deduces the theoretical result of the high degree intermodulation distortion caused by the nonlinearity of the amplifier. So that, it is become the key problem to improve the linearity of power amplifier for analog television transmitter for OFDM signal transmission.the froth chapter gives detailed analysis and comparison on series linearized technique of television transmitter power amplifier, emphasis is on power back-orTx feedback correction x feedforward correction and digital auto adaptive predistortion back on dual-LUT, and with the peculiarity of television transmitter amplifier, the chapter pointes out the technique feasibility and the restrictiveness in engineering realization of those correction scheme. Based on the result of analysis and study described above, this chapter gives a digital auto adaptive predistortion correction method-complex gain Look-Up Table (LUT) baseband digital predistortion technique, and computer simulation on this technique is carried out. This method has peculiarity of easy to realize, has relative less limitation on the element, and the correction loop convergence speedily. A good result of high degree intermodulation distortion compression is obtained in the computer simulation.In the fifth chapter, two correction schemes for analog television transmitter RF channel for digital television transmission are given, based on the result of theoretical analysis and computer simulation with the circuit transmitter model.This paper analysed in detail the technical requirement of analog television transmitter RF channel for digital television transmission in theory. Systematic study is made on the improvement of the linearity of analog television transmitter power amplifier for digital television signal transmission. This paper makes productive study on the analog television transmitter for digital television terrestrial transmission.更多还原