W-CDMA模拟预失真功率放大器设计

针对宽带码分多址(W-CDMA)功放的非线性失真问题,设计实现了工作频率范围在2 110～2 170 MHz放大器的预失真模块部分、驱动级、主功放,最终实现了适用于输出功率为41 dBm功率放大器的预失真系统.该系统利用二极管的非线性特性,调节二极管的偏置电压,以及补偿功放的非线性失真,有效地抑制临信道频谱再生,使输出信号的三阶交调、五阶交调分别改善了13 dB和10 dB.     

新型预失真功率放大器的研制

针对高线性功率放大器的实现途径,设计了一款应用模拟预失真技术与自适应预失真技术相结合的功率放大器。首先对预失真技术进行了原理性分析,阐述了模拟预失真技术的工作原理;然后给出了线性功率放大器的具体设计方案,功率放大器的频率范围为2 280～2 300 MHz,饱和输出功率为14 W,在1 dB功率压缩点(P-1)的情况下测得此功率放大器自身的三阶交调失真比为-12 dBc。实验结果表明,引入这种新型预失真技术后,线性功率放大器在P-1下的三阶交调失真比达到-20.78 dBc,三阶交调失真改善量约9 dB。证明了这种新型预失真技术方案有效并给出了这种新型线性化技术的前景与改进措施。     

一种新型线性化器的研究

介绍了固态功率放大器的线性化技术,并提出了一种新型反向并联肖特基二极管预失真器结构。对预失真器原理与基本结构进行了分析,通过改变预失真器中二极管的外加偏置电压和电阻值来调节失真信号的幅度和相位,达到线性化的目的。同时,利用ADS软件对加预失真器的固态功率放大器进行电路优化仿真,根据电路优化参数,对线性化固态功率放大器进行研制。测试结果表明,固态功率放大器三阶交调改善了15.8 dB,五阶交调也改善了10 dB,线性化改善效果明显,突破了工程化应用的技术瓶颈。     

采用90°分支电桥的C波段预失真线性化器

为了改善功率放大器的三阶交调失真,提出了一种基于90°分支线电桥的C波段预失真线性化器,使用肖特基二极管产生非线性信号。通过改变线性化器的偏置电压及电容,可调整线性化器的增益扩张和相位延迟特性,与功放级联后对功放的三阶交调失真有改善作用。将该线性化器应用到工作频率为7 GHz,饱和功率为20 dBm的放大器上,在输出功率回退5 dBm处对放大器的三阶交调有10 dBc的改善。     

射频模拟预失真器的研究与设计

利用小信号BJT放大器的非线性特性设计了一个有源模拟预失真器.通过调整小信号放大器的偏置状态和对失真信号的提取控制,使功放的三阶互调失真得到了明显的改善.双音实测数据表明,该预失真器使一个GSM基站功放在5 dB功率回退点附近的三阶互调失真改善了18 dB左右,与传统的射频预失真器相比,该预失真器对功放三阶互调失真的改善度提高了10 dB左右.     

欠采样在基带预失真功率放大器线性化的应用

从理论证实了欠采样在基带预失真中的可行性,将欠采样用在基带预失真系统上,降低了功率放大器失真信号的采样率而完整地保留了信号中的非线性信息.最后,利用欠采样理论构建了基带预失真功率放大器系统,得到了19 dB三阶交调失真的改善,与正常采样下(5倍输入信号Nyquist采样率)的三阶交调失真的改善度相比相当,从而降低了系统的复杂度及成本.     

K波段预失真电路设计

提出了一种基于单片集成电路的K波段预失真电路设计,采用GaAs 0.15μm HEMT工艺流片。该电路将主路信号与失真信号分离,利用并联分布的功放作为非线性产生器件,增大了两个功放输入功率差,具有较好的幅度和相位特性,芯片尺寸仅1.9mm×3.0mm。测试结果显示,在21GHz处,该预失真芯片可提供3dB增益扩张和20°相位压缩。级联功放后,在三阶交调抑制为-30dBc的条件下,功率放大器的输出功率从14dBm提高至17.5dBm。     

多载波航天测控雷达发射机功放的线性化

某航天测控雷达发射机采用速调管进行主功率放大,而速调管线性差,三阶交调指标不满足要求,影响雷达性能。该文利用三阶多项式来表征速调管的非线性特性,并根据测试数据确定多项式系数,计算出速调管增益压缩特性;然后提出一种顸失真方法,利用两路载波信号频率合成得到预失真三阶信号,将此信号与载波信号合成后送入速调管共同放大,通过调整预失真三阶信号的幅度和相位来抵消载波信号放大后产生的三阶交调信号而达到线性化。最后根据算出的速调管特性设置仿真条件进行了仿真。结果表明,此方法可使三阶交调指标改善10．5dB左右,从而使指标符合要求。该方法原理清晰,电路简单,效果明显,可以显著改善三阶交调,从而提高雷达性能。     

一种模拟预失真自适应线性化方法

针对射频功率放大器的非线性问题,提出一种基于两个复量多项式的模拟预失真电路,并根据射频功率放大器的响应用LMS(最小均方)算法自适应优化多项式的系数,从而使功率放大器的线性性能达到最佳。该预失真器的优点是电路简单,运算量少,适用于宽带通信。基于双频信号和WCDMA(宽带码分多址)信号对该预失真器进行了仿真测试。实验结果表明,该预失真线性化方法对交调失真分量抑制效果明显,ACPR(邻信道功率比)可改善至56.1dB,对功率放大器的非线性具有良好的补偿效果。     

采用二极管的模拟预失真毫米波功放线性化器

研制了一款用于毫米波频段的线性化器,采用模拟预失真技术,基于90°电桥和两个肖特基二极管,在外加直流偏置的情况下,产生预失真信号,通过矢量网络分析仪测试表明,当工作频率为30GHz时,其增益扩展了3～4dB,相位延迟了20°左右。将该线性化器与毫米波功率放大器级联,双音测试结果表明,当功放的输出功率为1dB压缩点回退3dB时,三阶交调指标在工作频率30GHz和31GHz时均改善了10dB左右。该线性化器结构简单、成本较低、实用性强。     

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。     

Two-Tone and Nine-Tone Excitations in Future Adaptive Predistorted Linearised Basestation Amplifiers of Cellular Radio

Linearisation of a radio basestation amplifier using a third order, a fifth order and a seventh order predistortion scheme is studied. Adaptive predistortion using a third order predistorter improved the amplifier intermodulation distortion (IMD) by between 6.4 dB and 33 dB from the third IMD power level (i.e., maximum power amplitude variation of the IMD), provided by the raw amplifier, as measured by a two tone test. The variation in improvement is due to changes in the input power level. Improvement increases as the input power is backed off from the 1 dB compression point. A fifth order predistorter will give an IMD improvement of 8.7 dB and 48.4 dB if properly adjusted. A seventh order predistorter (with the fifth complex coefficient fixed to zero) will show the best performance, particularly throughout a window (approximately from 1.5 dB to 3 dB away from the 1 dB compression point). The IMD improvement throughout this window within the high input range measures between 9.1 dB to 21.7 dB over that achieved with a fifth order predistorter. For a nine-tone test (with uniformly distributed random phase), a third order predistorter will hardly improve the worst IMD power level, provided by the raw amplifier. A fifth order predistorter, if properly adapted will give an IMD improvement of between 8.8 dB and 41.5 dB from the worst IMD level while a seventh order predistorter will give a close performance to that of a fifth order one. Fixing the predistorter coefficients enables a comparative study of the IMD power level improvement between 5th order fixed and adaptive predistorters, for a nine-tone excitation. A 5th order predistorter with its coefficients fixed to those values obtained for optimum IMD level at a backed-off power input value of 8.5 dB from the 1 dB compression point is found to maintain an IMD power variation better than 55 dB from fundamental power level, throughout the input range, up to the backed-off value.     

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。     

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.     

基于肖特基二极管的反射式可调预失真电路

为解决传统反射式预失真电路可调性不高、对功率放大器的邻信道泄漏比(ACLR)改善量小的问题,文 中提出了一种基于肖特基二极管的反射式可调模拟预失真电路。该电路由90°电桥、肖特基二极管以及偏置电路组 成。每条支路采用两个并联肖特基二极管产生非线性信号,以抵消功放的非线性失真。每一个肖特基二极管都有独立 的偏置电路,从而可以增加电路调节的自由度。通过改变每个肖特基二极管的偏压,可实现更大动态范围的幅度和相 位的补偿。基于此原理加工的S 波段模拟预失真电路对中心频率为3. 5 GHz 的Doherty 功率放大器进行线性化测试, 实验结果证明:加上提出的模拟预失真电路后,在输出功率为-28 dBm 时被测功放的ACLR 改善了14. 6 dBc 以上。     

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 analog compensation method for asymmetric IMD characteristics of power amplifier

The modulation frequency affects the asymmetric intermodulation distortion (IMD) products of a RF power amplifier. This effect reduces IMD cancellation performance of power amplifiers in connection with predistortion linearization. A phase extraction method to determine phase difference between upper and lower third-order IMD products and a phase compensation circuit using an envelope injection technique is proposed. The experimental results demonstrate a significant improvement in the third-order IMD cancellation performance.     

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.