基于多项式与查找表的预失真技术研究

为补偿功率放大器固有的非线性,提出了一种新型的预失真器。该预失真器结合查找表和多项式两种常用的预失真方法实现,在查找表中存储分段低阶多项式系数,根据输入信号的幅度查表得到相应的多项式系数对输入信号进行预失真处理。仿真结果表明,该预失真器对互调失真（IMD）的改善优于多项式预失真器,能有效改善信号因功放非线性失真而导致的信号星座图扭曲及频谱再生,提高通信系统的性能。     

一种新的用于射频功率放大器的预失真器

研究了一种新的预失真线性化电路,他由2路谐波发生器组成,每个谐波发生器都由2个工作于不同偏置电压下的肖特基二极管、电容、电阻和3 dB电桥耦合器(Hybrid)构成。通过调节二极管的偏置电压,可分别产生IM3或IM5。将此预失真线性化电路用于5 W射频功率放大器中,分别独立地对消IMD3和IMD5。双音测试表明,IMD3和IMD5分别改善了14 dBc和9 dBc。     

一种基于开路短截线相位补偿的模拟预失真电路

传统的单路并联式模拟预失真电路,其可调性不高,对功率放大器的三阶交调改善量也非常有限。为了解决上述问题,提出了一种能用开路短截线进行适当相位补偿的S 波段模拟预失真电路。该模拟预失真电路使用肖特基二极管产生三阶交调信号,通过改变开路短截线的长度,来调整基波信号与三阶交调信号的相位差,使它的特性跟功率放大器的特性相反,从而抵消功放的三阶交调信号。实验结果表明,在3.5 GHz 的AB 类功放的1 dB压缩点处,加模拟预失真电路后,三阶交调量改善了约34 dB。     

基于增益扩展现象的线性化技术在Doherty功放中的应用

在分析Doherty放大器特性基础上,研究了利用Doherty具有增益扩展特性的放大器线性化技术.深入分析了Doherty功放中辅助功放的栅压变化对增益扩展特性的影响,并讨论了据此将具有增益扩展特性的前级Doherty功放作为模拟射频预失真器与末级Doherty功放进行级联而构成的线性化功放.最后根据这一原理,采用一对MRF21010功放管所设计并优化的Doherty模拟预失真功率放大器与前级为平衡放大器、末级为相同Doherty功放的级联电路相对照,表明三阶互调可以改善15dB,效率提高2%.研究结果对高效率、高线性功放的设计具有实际意义.     

An adaptive digital predistortion for compensating nonlinear distortions in RF power amplifier with memory effects

In this paper, an adaptive digital predistortion based on a memory polynomial model is proposed in order to linearize the power amplifier with memory effect. The coefficients of the power amplifier model have been extracted using a least square method and those of predistortion have been identified by applying an indirect learning structure. Finally, the performance of digital predistortion has been demonstrated using the simulation of the power amplifier and the digital predistortion excited by a modulated 16 QAM signal in Matlab software. According to the simulation results, the criterion of adjacent channel power ratio (ACPR) declined by around 15 dB and the input/output power spectrum density of the power amplifier has quite similar curves. The linearized power amplifier output spectrum demonstrates the superiority of the proposed predistorter in eliminating the spectral regrowth which is caused by the memory effect in comparison to the other linearization methods.     

Characterization of a low-noise linearized microwave power amplifier module

An X-band, low-noise, linearized microwave power amplifier module consisting of a low-noise solid-state amplifier (SSA), predistortion linearizing circuit, and low-gain helix traveling wave tube (TWT) is designed and tested in order to demonstrate both reduced noise figure and suppressed intermodulation distortion ratio. Two-tone intermodulation distortion (IMD) ratios are predicted from simulations obtained from modeling of the TWT, linearizing circuit, and SSA by the use of Agilent's Advanced Design System simulation code. Simulated IMD ratios are in good agreement with measured results. Measurements show a noise figure of 2.2 dB at 9.5 GHz and the third-order IMD ratio of -53 dBc at 10 dB input back off from the input P1dB point. It is found that both noise figure and IMD ratio are significantly improved compared with conventional helix-TWTs and microwave power modules.     

Novel Digital Compensation Approaches for Envelope Tracking Amplifiers

This paper considers the compensation of the envelope tracking (ET) amplifier. In particular, we propose a new predistortion architecture for the ET amplifier. In addition, we develop new algorithms for time misalignment compensation between the input signals of the ET amplifier and compare the methods to a previously presented method. Our results indicate that using the proposed architecture with optimal predistorter, we achieve over 40 dB better adjacent channel power than using a previously presented architecture. In addition, the time misalignment compensation methods give very accurate timing estimates. The time misalignment compensation with the predistortion reduces spectral regrowth due to the nonlinear ET amplifier and improves the power efficiency of the ET amplifier.     

一种新的分数阶记忆多项式预失真器

该文针对由记忆多项式设计的功率放大器预失真系统,提出了一种新的分数阶记忆多项式预失真器。提出预失真多项式是在常用记忆多项式基础上,通过去掉偶数阶项增加分数阶项以提高线性化性能。文中给出了分数阶记忆多项式的表达式,并给出了相应的系数估计算法。仿真分析表明,针对Wiener-Hammerstein和记忆多项式模型的功率放大器,在两种典型记忆多项式预失真的基础上可以分别得到10 dB和8 dB的带外谱抑制增益。相应的FPGA实现表明该预失真多项式总体硬件资源增加的代价并不高,易于在实际系统中应用。     

一种RF模拟预失真放大器的实现

预失真线性化技术理论上是最简单的 RF 功率放大器线性化技术。本文利用场效应管偏置于可变电阻区时的栅压控制变阻特性构成模拟射频预失真器,在对放大器线性化的同时还可提供一定的增益。为了验证电路的有效性,分别使用双音信号和 W-CDMA 信号进行测试,结果表明3阶互调改善9dB,邻道功率比(ACPR)改善 5dB。     

Amplifier linearization using simultaneous harmonic and basebandinjection

A novel linearization scheme utilizing injection of distortion signal at the input of amplifier is described. Harmonic and baseband signal generated by predistortion circuits is fed to the input of the main amplifier and by controlling the power level of the harmonic and baseband signal properly, mixing products can be made to cancel out with the FET inherent distortion signals. Unlike many other techniques, no precise phase adjustment is required for the RF signal path. For verification, the two-tone performance of a constructed linearized amplifier is measured and a reduction of the third-order IMD power level of about 27 dB is observed     

An adaptive predistorter for a power amplifier based on adjacentchannel emissions [mobile communications]

A slowly adapting predistorter is presented. The approach is to minimize the transmitter output power in spectral regions occupied only by intermodulation (IM) products. In this way, only a spot power measurement is required. This technique relies on the principle that the power amplifier's characteristics vary slowly with time. By monitoring the out-of-band power one can obtain an estimate for the distortion introduced by the power amplifier. Adaptation is accomplished by iterative adjustment of the predistorter parameters to minimize the IM power. For a polynomial predistorter, the authors analytically demonstrate that the IM power is a quadratic function of the coefficients. A variety of algorithms therefore apply. The authors present an analog static predistortion linearization circuit that uses the envelope of the baseband signal to generate the nonlinear functional used in predistorting the input signal. The improvement obtained with an amplitude-modulated input signal was 15 dB in the third- and 5 dB in the fifth-order intermodulation products. The IM improvement could be maintained with the use of a robust direct search algorithm     

基于毫米波GaN固态功放的预失真线性化器

研制了一款用于毫米波GaN 固态功放的预失真线性化器。采用预失真线性化技术,通过调整I、Q 两路正交电路(I 路由线性可调衰减器构成,Q 路由二极管非线性电路构成)的外加偏置电压,可以实现预失真线性化器的幅度和相位分别可调。将该线性化器与工作频率为30 GHz 的毫米波GaN 固态功放级联测试,双音激励信号频率间隔为5 MHz,三阶互调(IMD3)可以改善约10 dB。     

一种有效的基于宽带功率放大器强记忆效应特性的PMEC预失真方法

针对宽带功率放大器的强记忆效应特性,论文提出了一种新的预失真方法PMEC (Parallel MP-EMP-CIMT),该方法基于记忆多项式(MP),包络记忆多项式(EMP)及记忆时刻信号交叉项(CIMT)3个基函数构造预失真器。与传统混合记忆多项式(HME)方法相比,PMEC方法增加了记忆时刻信号间的交叉相乘项,此外,为了解决系统复杂度高的问题,对EMP子预失真器进行了简化并截断了CIMT子预失真器的高阶非线性项。实际测试结果表明,PMEC方法比MP方法和HME方法能带来更好的线性化效果,与MP方法相比,PMEC方法将输出信号的三阶邻信道功率比(ACPR)降低了1.07 dB/1.32 dB,预失真系数量节省了18.75%;与HME方法相比,PMEC方法利用79.59%的预失真系数将输出信号的三阶ACPR降低了0.2 dB/0.99 dB。     

Rational function based predistorter for traveling wave tube amplifiers

A new scheme for the compensation of traveling wave tube amplifier nonlinearities is proposed and analyzed in this paper. The approach is based on rational function models of the amplifier AM-AM and AM-PM conversions. Amplitude and phase predistortion are performed separately. The phase predistortion is a function of the output of the amplitude predistortion part of the predistorter, instead of the input signal amplitude of the predistorter. Computer simulations reveal an improved performance compared to published techniques and suggest that with the proposed technique the transmit power amplifier can operate far into its nonlinear region. The transfer characteristics of the cascade of the amplifier and the proposed predistorter match the optimum transfer characteristics of a saturating device.     

基于改进型径向基函数神经网络的功放线性化

提出了一种基于改进型径向基函数神经网络(MRBFNN)的数字预失真线性化模型,用于更为精确地矫正宽带射频功率放大器的动态非线性。该神经网络模型的输入层使用传统的延时抽头以补偿功放的线性记忆效应,同时对每个抽头进行级数展开用于补偿功放的非线性记忆效应,从而更好地抑制功放的动态非线性失真。文中使用WCDMA 三载波信号对一个460MHz 的Doherty 功率放大器进行数字预失真线性化实验。实验结果表明,与传统数字预失真线性化模型相比,基于改进型径向基神经网络的数字预失真线性化模型能更好地抑制宽带功放动态非线性引起的带外频谱再生,其三阶互调(IMD3)失真最多可以抑制23dB,大大提高了功放的线性度,验证了所提出的数字预失真线性化模型的有效性。     

宽带系统中有记忆大功率功放的数字预失真器研究

针对高峰均比的宽带输入信号,提出了一套联合峰均比抑制技术和基带自适应预失真技术的数字预失真器设计方案,并仿真了峰值抵消算法和自适应预失真算法.结果表明对于峰均比为8.4 dB的输入信号,经过1.5 dB的削峰处理后,预失真器改善带外频谱抑制27 dB,非常有效地补偿了功放的非线性失真,提高了功放效率,对发射机功放线性化技术有一定的实用价值.     

A wide dynamic range analog predistortion-type linearizer using self-cancellation scheme

A new radio frequency linearized power amplifier (LPA) system for wideband-code-division-multiple-access (WCDMA) application is demonstrated. The main amplifier is a parallel combination of drive amplifiers, and the same type of drive amplifier is also used to generate the predistortion signal. Self-cancellation of the intermodulation-distortion (IMD) components is obtained by the generic identity between the nonlinear characteristics of the main amplifier and the predistortion signal, both of which are originated from the same type of devices. Such self-cancellation scheme exhibits the improvement of 13 dB in the adjacent channel leakage ratio (ACLR) for WCDMA signal excitation.     

Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications

This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for an IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of -46 dBc at a 4-W average output power with a cancellation of 13.4 dB.     

一种简单RF预失真电路的研究

文章介绍一种基于肖特基二极管的预失真器及其工作原理。预失真器主要由一个肖特基二极管和直流偏置电阻组成,利用二极管的非线性,产生与功放相反的幅度失真与相位失真。通过调节二极管的偏压来调整预失真器的工作状态,使功率放大器在不同输出功率下得到最好的线性度改善。设计实际电路经实验发现,对于应用在C波段的某功率放大器,在不同的输出功率下IMD3的改善不同。在功率放大器1dB增益压缩点处IMD3改善了5dB,而在其他功率点处IMD3最大甚至可以改善20dB。     

Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology

An analogue predistorter using a distortion generator based on a two-stage radio frequency mixer topology is presented. The proposed distortion generator achieves fundamental signal cancellation without using a signal cancellation loop or a resonant circuit, thus it generates an error signal that predominantly consists of unwanted intermodulation distortion (IMD). Measurements are performed using multi-tones, WLAN- and Terrestrial Trunked Radio (TETRA)-modulated signals. Distortion generator provides high levels of IMD and achieves more than 40 dB fundamental signal cancellation across a bandwidth of 120 MHz. A proof-of-concept predistorter was constructed to validate the usefulness of the proposed distortion generator, which achieves up to 15 dB suppression of IMD and adjacent channel power ratio at the output of a power amplifier. Distortion generator and predistorter gave similar results at multiple frequencies between 920 MHz and 2 GHz, with different test signals having bandwidths ranging from 25 kHz to 120 MHz.