【作者】 何敏；

【导师】 张玉明；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 随着现代无线通信技术的发展,射频功率放大器作为无线通信系统发射机中的关键部件,其性能的优劣直接影响通信质量的好坏,因而得到了越来越广泛的重视和深入研究。现代无线通信系统如CDMA2000,WCDMA,OFDM等,希望在快速移动的环境下获得越来越大的数据传输速率,这就要求这些通信系统的调制信号变化极快和较高的射频信号峰均值比,从而使得功率放大器必须要有较高的线性度。而功率放大器的线性度的提高往往是以功率回退的形式获得,这样就导致了放大器效率的急剧下降,因此在满足设计所需的线性度要求下,如何提高功率放大器的工作效率就显得非常重要。Doherty技术在低输出功率情况下能达到大输出功率情况下的工作效率,可以很好地兼顾达到高效率和高线性度,并且实现方式简单,成本低廉,而且Doherty技术与数字预失真技术结合的结构具有更高的线性度和更大的价值。本文基于典型Doherty功率放大器理论基础上,加入微带补偿线后,设计了一个L波段36W平均输出功率的高效率Doherty功率放大器电路实例。该文简要介绍了射频功率放大器的主要性能指标,详细分析研究了放大器设计中要考虑的稳定性分析,匹配技术,负载牵引技术,Doherty放大器工作原理及峰值放大器偏置对Doherty放大器的影响等问题,重点是以Freescale公司的MRF6S19060N器件为功放管模型,通过安捷伦公司的ADS仿真软件,在经典Doherty放大器电路结构上加入微带补偿线,使得载波和峰值放大器输出端的输出信号的附加相位移变化一致,相位差不变,而微带线的高特征阻抗可以有效的阻止峰值放大器的功率泄露,从而得到在1960MHz,平均输出功率约为36W时,其临信道功率泄漏比小于-45dBc,功率附加效率高达42.2%,三阶交调失真小于-26dBc并与同种条件下未加微带补偿线的Doherty功率放大器,AB类放大器进行仿真比较验证,其功率附加效率比前者提升了17.3%,比后者提高了25%以上,其三阶交调失真比未加微带补偿线的Doherty功率放大器也改善了3dB左右,最后使用Autocad画图软件完成了实物制作。更多还原

【Abstract】 As modern wireless communication technology develops, RF power amplifiers are becoming the attractive study, because they are the key component of wireless mobile communication transmitter and communication quality depends on high performance of RF power amplifiers. Modern wireless communication systems such as CDMA2000, WCDMA, OFDM, and so on, are intended to maximize the data rate in a fast moving environment. The modulated signals of these systems vary rapidly and have high peak-to-average power ratios resulting in high linearity for power amplifiers. The improvement of linearity of power amplifier is mainly achieved by backing off power, but the efficiency of power amplifier will quickly decrease. So it is very important to improve the efficiency of power amplifiers above the demanding linearity. Doherty technique has both of high efficiency and high linearity and can achieve high efficiency at low output power as same as at high output power and it has advantages of easy implement and low cost. Moreover, the combination of Doherty technique and digital pre-distortion technique will achieve higher linearity and more importance for applications.Based on conventional Doherty technique, a L-band 40W high-efficiency Doherty power amplifier with microstrip offset lines was designed in this thesis. The main performances of RF power amplifiers is introduced and the problems related to power amplifier design such as stability, matching methods, Load-Pull theory, Doherty theory, effect of peaking amplifier stage bias on Doherty PA ,and so on , are analyzed in detailed. The emphasis is put on using Freescale’LDMOS transistor MRF6S19060N as the power amplifier model and Angilent’s simulation software ADS, adding microstrip lines to the conventional Doherty PA to make output signals phase difference constant between carrier amplifier and peak amplifier and to prevent power leakage from peak amplifier because of high impedance of microstrip. In this case, the ACLR less than -45dBc,the power added efficiency(PAE) high to 42.2% and the third-order intermodulation distortion(IMD3) less than -26dBc are achieved with 36W output power 6dB backed off from the compression point at frequency of 1960MHz. Compared with the Doherty amplifier without microstrip offset lines and balanced class AB amplifier, the PAE of the Doherty amplifier with offset lines is improved 17.3% higher than the former one and 25% higher than the balanced class AB amplifier. Moreover, the IMD3 of the Doherty amplifier with offset lines is improved 3dB less than the Doherty amplifier without microstrip offset lines. At last, the PCB of the Doherty power amplifier has been fabricated.更多还原