摘要
射频功率放大器是现代无线通信系统发射机中的关键模块，其性能的优劣直接影响着通信的质量和效率，目前大多数的功放模型和线性化方法都局限于窄带应用，当信号带宽增大导致放大器记忆效应明显时，传统的线性化方法对功放非线性的补偿效果就会变得很差，为了改善宽带放大器的线性度，近年来考虑记忆效应的功放建模和线性化方法成为新的研究趋势。
深入研究宽带通信系统中功率放大器的非线性机制及记忆效应，分析了记忆效应的现象及产生原因，论述了三类非线性放大器模型：无记忆模型，准无记忆模型和考虑记忆效应的模型。分别用极坐标，正交拓扑以及多项式函数的形式推导了准无记忆模型的输入输出关系，归纳出利用双音测量数据提取多项式系数的步骤。重点论述了记忆多项式模型的构造原理，包括一致时延项模型和非一致时延项模型，比较了它们的建模策略和复杂度，并以Motorola公司的MRF9742功放管为例，提出了一种新的更易于实现的非一致时延分支项算法：类正弦函数确定法。
利用记忆多项式建模法对传统预失真技术进行改进，提出非一致时延记忆多项式预失真技术，并着重分析了记忆预失真发生器的构造原理。设计了一个非一致时延记忆预失真线性化功放系统，利用ADS仿真分析MRF9742模型的非线性特性和记忆效应，比较了传统预失真和非一致时延预失真的线性化效果，仿真结果证明在宽带应用中，用类正弦函数算法构造的非一致时延预失真能迅速有效地抑制输出频谱中的互调失真产物，大幅提高功率放大器的线性度。
Radio frequency power amplifier is the key component of the transmitter inmodem wireless communication system, and its performance highly affects thecommunication quality and efficiency. At present, most power amplifier models andlinearization methods are limited to narrowband application. When memory effects ofthe amplifier become obvious due to widen of signal bandwidth, compensation effectsof the traditional linearization technique can not be satisfying. In order to improve thelinearity of wideband amplifiers, research on modeling and linearization of poweramplifiers considering memory effects has become a new trend in recent years.
Nonlinearity and memory effects of power amplifiers in widebandcommunication system are deeply analyzed including the phenomenon and sources ofmemory effects. There types of nonlinear amplifier models: memoryless model,quasi-memoryless model and memory model are presented. First, input-outputrelations of the quasi-memoryless model are developed respectively in polar,quadrature and polynomial function versions. Then the emphasis is laid on theconstruction principle of the memory polynomial model including memorypolynomial with unity time delay taps and memory polynomial with non-uniformtime delay taps. Modeling strategy and complexity of these two memory models arecompared and a new algorithm of realizing non-uniform time delay taps:sinusoidal-like function computation is put forward bases on MRF9742 powertransistor.
Traditional predistortion technique is improved using memory polynomialmodeling method. Non-uniform time delay memory polynomial predistortiontechnique and the realization of memory predistorter are represented in details. On thebasis of above analyses, a practical MRF9742 linearization power amplifier system isdesigned. First, nonlinear characteristics and memory effects of MRF9742 model aresimulated and analyzed using ADS software. Then linearization effects of traditionalpredistortion and non-uniform time delay predistortion are compared and the simulation results prove that non-uniform time delay predistortion techniquedepending on sinusoidal-like function computation can suppress the intermodulationdistortion products of the power amplifier system and improve its linearity greatly.
引文
[ 1 ] J. Vuolevi, T. Rahkonen, J. Manninen. Measurement Technique for Characterizing Memory Effects in RF Power Amplifiers. IEEE Trans. Microwave Theory Tech., 2001, vol.49 (8):1383～1389
[2] 谭兴.用 Volterra 级数描述非线性系统时Volterra 核的计算.贵州工学院学报, 1991, (20):67～73
[3] W. Bosch, G. Gatti. Measurement and Simulation of Memory Effects in Predistortion Linearizers. IEEE Trans. Microwave Theory Tech., 1989, vol.37 (12): 1885～1890
[4] H. Ku, M. D. McKinley, J. S. Kenney. Quantifying Memory Effects in RF Power Amplifiers. IEEE Trans. Microwave Theory Tech., 2002, vol. 50 (12): 2843～2849
[5] S. Boumaiza, F. M. Ghannouchi. Thermal Memory Effects Modeling and Compensation in RF Power Amplifiers and Predistortion Linearizers. IEEE Trans. Microwave Theory Tech.,2003, vol.51 (12): 2427～2433
[6] H. Ku, J. S. Kenney. Behavioral Modeling of Nonlinear RF Power Amplifiers Considering Memory Effects. IEEE Trans. Microwave Theory Tech., 2003, vol.51 (12): 2495～2504
[7] S. Forestier, N. Maslennikov, B. Vassilakis. Theoretical and Experimental Investigations on Nonlinear Capacitance and Loading Effects on Power PHEMT's Linearity. 33rd European Microwave Conference. Germany. 2003: 81～84
[8] M. C. Jeruchim, P. Balaban, K. S. Shanmugan. Simulation of Communication Systems:Modeling, Methodology, and Techniques. Kluwer. 2001: 21～25
[9] J. Goel, A.Katz. Workshop on Advances in Amplifier Linearization. IEEE MTT-S Int.Microwave Symp. Dig. WMD Workshop, USA. 1998
[10] J. C. Pedro, N. B. Carvalho. Intermodulation Distortion in Microwave and Wireless Circuits.Norwood, MA: Artech House, 2003
[11] P. B. Kenington. High Linearity RF Amplifier Design. Norwood, MA: Artech House, 2000
[12] N. Pothecary. Feedforward Linear Power Amplifiers. Norwood, MA: Artech House, 1999
[13] Powerwave Technologies Application Note. Multi-Carrier Power Amplifiers for WCDMA Wireless Systems. 1998. www.powerwave.com
[14] G. Fischer, W. Eckl. On the Benefits of GaN RF Power Devices for Mobile Communication Base Station. Workshop GaN-Electronik, Bonn, Germany, 2002
[15] A. A. M. Saleh. Frequency-independent and Frequency-dependent Nonlinear Models of TWT Amplifiers. IEEE Transaction on Communications. Vol.29(l l):1715~1720
[16] Y. Yang, J. Yi, J. Nam, et al. Behavioral Modelling of High Power Amplifiers Based on Measured Two-tone Transfer Characteristics. Microwave Journal, 2000:90～104
[17] Agilent Application Note 1298. Digital Modulation in Communications Systems-An Introduction. http://cp.literature.agilent.com/litweb/pdi75965-7160E.pdf
[18] J. Vuolevi, T. Rahkonen. Distortion in RF Power Amplifier. Norwood, MA: Artech House,2003
[19] A. Khanifar, N. Maslennikov, B. Vassilakis. Bias Circuit Topologies for Minimization of RFAmplifier Memory Effects. 33rd European Microwave Conference, Germany. 2003:1349～1352
[20] N. L. Gallou, J. M. Nebus, E. Ngoya, et al. Analysis of Low Frequency Memory and Influence on Solid State HPA Intermodulation characteristics. IEEE MTT-S Int. Microwave Symp. Dig. Phoenix, Arizona, 2001
[21] N. B. de Carvalho, J. C. Pedro. A Comprehensive Explanation of Distortion SidebandAsymmetries. IEEE Transactions in Microwave Theory and Techniques, 2002,vol.50(9):2.90～2101
[22] N. B. de Carvalho, J. C. Pedro. Two-Tone IMD Asymmetry in Microwave Power Amplifiers.IEEE MTT-S Int. Microwave Symp. Dig. Boston, MA, 2000:445～448
[23] S. Nuttinck. RF Performance and Thermal Analysis of AlGaN Power HeMTs in Presence of Self-Heating Effects. IEEE MTT-S Int. Microwave Symp. Dig. Seattle, WA, 2002:921～924
[24] D. J. Williams, J. Leckey, P. Tasker. A Study of the Effect of Envelope Impedance on Intermodulation Asymmetry Using a Two-tone Time Domain Measurement System. IEEE MTT-S Int. Microwave Symp. Dig. Seattle, WA, 2002:1841～1844
[25] A. R. Kaye, D. A. George, M. J. Eric. Analysis and Compensation of Bandpass Nonlinearities for Communications. IEEE Transaction on Communications, vol.20, 1972,965～972
[26] S. C. Cripps. Advanced Techniques in RF Power Amplifier Design. Norwood, MA:Artech House, 2002
[27] R. Raich, H. Qian, G T. Zhou. Orthogonal Polynomials for Power Amplifier Modeling and Predistorter Design. IEEE Trans, on Vehicular Technology, 2003, vol.1:512-519
[28] L. Ding, G. T. Zhou, Z. Ma, et al. A Robust Digital Baseband Predistorter Constructed Using Memory Polynomials. IEEE Trans. Communication., 2004, vol.52:159～165
[29] H. Ku, J. S. Kenney. Behavioral Modeling of RF Power Amplifiers Considering IMD and Spectral Regrowth Asymmetries. IEEE MTT-S Int. Microwave Symp. Dig., 2003:799～802
[30] H. Ku, J. S. Kenney. Analysis of Performance for Memoryless Predistortion Linearizers Considering Power Amplifier Memory Effects. Topical Workshop on PA for Wireless Communications, CA, USA, 2003
[31] J. S. Kenney, W. Woo, L. Ding, et al. The Impact of Memory Effects on Predistortion Linearization of RF Power Amplifiers. IEEE Proc. of the 8th International Symp. on Microwave and Optical Technology, Canada, 2001:189～193
[32] F. Zavosh, M. Thomas, C. Thron, et al. Digital Predistortion Techniques for RF Power Amplifiers with CDMA Applications. Microwave Journal, 1999:23-35
[33] S. Andreoli, H. G. McClure. Digital Linearizer for RF Amplifiers. IEEE Transactions on Broadcasting, 1997, vol.43(1):12～19
[34] Y. Nagata. Linear Amplification Technique for Digital Mobile Communication. IEEE 39th Vehicular Technology Conference, 1989, vol. 1: 159～164
[35] M. Ghaderi, S. Kumar, D. E. Dodds. Fast Adaptive Polynomial I and Q Predistorter with Global Optimisation. IEEE Proc. Commun., 1996, vol. 143(2):78～76
[36] S. P. Stapleton, F. C. Costescu. An Adaptive Predistorter for a Power Amplifier Based on Adjacent Channel Emissions. IEEE Transactions on Vehicular Technology, 1992, vol. 41(1): 49～55
[37] 钱业青，姚天任．记忆非线性功率放大器的神经网络预失真．计算机工程与应用，2004，40(21)：100～103