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微波功放线性化前馈技术研究
【作者】 张娟；
【导师】 延波；
【作者基本信息】 电子科技大学 ， 电磁场与微波技术， 2008， 硕士
【摘要】 随着以WCDMA为代表的第三代移动通信技术的发展,线性调制技术正得到越来越广泛地应用。但包络变化的调制信号经过非线性射频功率放大器后会产生严重的交调分量,为此要实现宽带调制、多载波应用,同时减小邻信道干扰以满足通信系统的误码率要求,就对基站发射机功放的线性指标提出了苛刻的要求。本文首先分析了功率放大器的非线性特性,包括其幅度非线性、相位非线性以及功放的非线性指标;在此基础上,分析比较了功率回退法、负反馈法、预失真法、前馈法及其与自适应算法的结合等几种线性化技术的优缺点;并根据3GPP对WCDMA发射机功率放大器的射频指标要求,进行方案论证,确立了本课题的前馈线性功放的电路结构、指标分配以及器件选取。本设计采用MW4IC2230和MRF6S21140H以两级级联的形式构成主功率放大器,用ADS分别对其进行了输入输出匹配电路设计,以此来改善功放管的小信号增益、回波损耗、1dB压缩点输出功率以及交调分量,并粗略估算了系统中所采用的辅助放大器、误差放大器、功分器、定向耦合器、3dB分支线电桥、衰减器和移相器等有/无源器件所需指标。然后在ADS中将各部件级联对该方案进行了可行性验证。仿真结果显示,主功率放大器的交调失真分量得到了很好的抑制,表明该方案满足于系统指标要求。基于对仿真结果的分析,最终选定了所需要的器件,借助ADS和HFSS对该系统各组件逐一进行了仿真和设计。对电路进行了设计和加工,最终以实物的形式验证了方案的可行性。经过对各模块的反复调试,系统的性能基本与仿真结果吻合,基本达到预期目标。在文中详细给出了各组件以及整个系统的测试数据。测试结果表明,前馈功放系统在双音输出功率12.5W时三阶交调系数小于-44dBc,可以使主功率放大器的三阶交调系数有21dB的改善,且邻信道功率泄漏比(ACPR)的估算结果小于-47dBc,基本达到WCDMA发射机的射频指标要求。
【Abstract】 With the development of WCDMA-leaded 3 Generation mobile communication technology, the technology of linear modulation has been applied more and more widely, but there comes serious intermodulation when the envelope-varied modulation signal is amplified by non-linear RF power amplifier. So more critical requirements have been put forward for linear index of the PA in the base-station transmitter, if it is used in broadband modulation, multicarrier condition, and meanwhile to decrease the adjacent channel power rejection(ACPR) in order to get lower the Bit-Error Rate(BER).The pre-distortion circuit topology is simpler than the feed-forward one, but it can’t meet the requirement of the linearity of the PA in transmitter; but the feed-forward system can achieve the performance of closed-loop system, and broadband characteristic, stability behavior. The application of feed-forward system is widespread in based-station and other communication equipment.First of all, the non-linear characteristic of PA has been analysed in this paper, include: amplitude nonlinear, phase nonlinear, and other nonlinear index. Furthermore, the comparative analysis on the linearization techniques has been set, such as power back, negertive feedback, pre-distortion, feed-foreward, and the technology of combination with the adaptive algorithm. And then, based on the theoretical study, the paper makes an overall scheme proof, according to the standards of 3GPP. Lastly, the index allocation, circuit structure, and components needed, have been established.According to the target index, MW4IC2230 and MRF6S21140H are selected to cascad to realize main PA, the Agilent ADS simulation was used to design the input/output match network, in order to improve the small signal gain, return loss, P1dB, and intermodulation part, and assess the needed index of the passive component in the system----such as assistant amplifier, error amplifier, divider, directional coupler, 3dB branch-line bridge, attenuator, phase shifter and etc. Then use ADS to testify the cascade circuit module. The simulation results indicate that: the inermodulated distortion of main amplifier has been restrained well, and proves that the needed index can be satisfied by this scheme.The Agilent ADS simulation confirmed that the scheme is able to have good linear performance under the double-tune input, the third-order intermodulation had remarkable improvement. The entire forward feed power amplifier system has been realized, and the debugging and test have also been made.The test result indicated that feed-forward power amplifier double-tune test (12.5W output), the third-order intermodulation coefficient is smaller than -44dBc, may make 21dB improvement on third-order intermodulation of the main power amplifier’s coefficient, and the estimated ACPR is higher than -47dBc. The design of this paper achieves good performance, theoretically satisfies 3GPP standards to the WCDMA based-station transmitter.