基于循环平稳特性的欠采样宽带数字预失真研究

为了解决行波管(TWT)宽带数字预失真(DPD)中反馈回路ADC采样率过高的问题，该文利用信号的循环平稳特性证实可通过欠采样下的输出信号估计功放的非线性模型参数，然后由功放非线性模型参数和输入信号可恢复出与高采样率下效果相似的功放输出信号，最后通过传统的间接学习结构对功放进行数字预失真以实现行波管的线性化。为了验证该方法，利用20 MHz LTE信号驱动一只55 W的X波段行波管放大器(TWTA)。数字预失真反馈回路的ADC采样率从61.44 Msps降低至6.144 Msps和3.072 Msps，但线性化效果变化不大，表明欠采样方法是有效的。     

一种新型数字预失真算法的设计

针对WCDMA系统中功率放大器的非线性特征,设计了一种基于Volterra级数的有记忆数字基带预失真算法,能够自适应地补偿功放的非线性.理论分析和计算机仿真验证了该算法的有效性和实用性.     

A hybrid digital/RF envelope predistortion linearization system for power amplifiers

This paper presents an adaptive wide-band digitally controlled RF envelope predistortion linearization system for power amplifiers (PAs). A field-programmable gate-array-based lookup table is indexed by a digitized envelope power signal, and instantaneously adjusts the input signal amplitude and phase via an RF vector modulator to compensate for the AM-AM and AM-PM distortion. The advantages of this predistortion architecture over conventional baseband digital approaches are that a 20%-33% wider correction bandwidth is achievable at the same clock speeds, and linearization can be performed without the need for a digital baseband input signal. The timing match between the input RF signal and predistorting signal, which is one of the critical factors for performance, was investigated and adjusted to obtain optimum performance. Using three-carrier cdmaOne and wide-band multitone signals, the linearization performances for a 0.5-W GaAs heterostructure field-effect transistor, a 90-W peak-envelope-power (PEP) silicon LDMOS PA, and a 680-W PEP LDMOS PA were examined. In addition, the predistortion performance variation for different signals was studied in terms of signal envelope statistics, output powers, and PA power capacities.     

高功率毫米波回旋行波管宽带输出窗设计

首先利用场匹配理论建立传输级联矩阵对回旋行波管输出窗进行解析分析。在理论分析的基础上,通过数值计算得到回旋行波管宽带蓝宝石输出窗的初步结构和尺寸,然后利用三维高频分析软件HFSS进行仿真验证。通过大量计算与仿真,为Ka波段TE01模回旋行波管设计出驻波比小于1.2的输出带宽约为6GHz,相对带宽大于17%的高性能3层窗片结构蓝宝石输出窗。通过冷测实验研究表明仿真计算结果与冷测结果基本一致。     

一种S波段宽带GaN放大器的设计

氮化镓功率管的宽带隙、高击穿电场等特点,使其具有带宽宽,高效特性等优点。为了研究GaN功率放大器的特点,使用了AgilentADS等仿真软件,进行电路仿真设计,设计制作了一种s波段宽带GaN功率放大器。详述了电路仿真过程,并对设计的宽带GaN功率放大器进行测试,通过测试的实验数据表明,设计的宽带放大器在s波段宽带内可实现功率超过44dBm的功率输出,验证了GaN功率放大器具有宽带的特点。     

Measurement of a filter using a power detector

This paper presents experimental results on the measurement of the magnitude and phase response of RF and baseband signal paths made with a power detector. The frequency response is obtained by measuring the magnitude and phase of the output of the power detector when the forward path is excited by a pair of tones. This technique provides a means for making vector measurements using a scalar detector. Instruments, like network analyzers, commonly use a mixer and sinusoidal source to downconvert the signal for digitization and measurement. The downconversion in this paper is performed using a power detector and an extra tone in the excitation signal itself, drastically reducing hardware complexity. Important applications of this technique include the characterization of the digital-to-antenna path of a software radio and the equalization of the antialiasing filter in a wide-band arbitrary waveform generator. Three examples of measurement, one at low frequency and two others at radio frequencies, show that the errors in the measured response are comparable to those obtained using conventional network analyzers     

Full-CMOS 2-GHz WCDMA direct conversion transmitter and receiver

This paper presents a full-CMOS transmitter and receiver for 2.0-GHz wide-band code division multiple access with direct conversion mixers and a DC-offset cancellation scheme. The direct conversion scheme combined with a multiphase sampling fractional-N prescaler alleviates the problems of the direct conversion transmitter and receiver. Digital gain control is merged into the baseband filters and variable-gain amplifiers to optimize the linearity of the system, reduce the noise, and improve the sensitivity. Variable-gain amplifiers with DC-offset cancellation loop eliminate the DC-offset in each stage. The chip implemented in 0.35-/spl mu/m CMOS technology shows the experimental results of 6 dBm maximum output power with 38-dB adjacent channel power rejection ratio at 1.92 MHz, 50-dB dynamic range, and 363-mW power consumption in the transmitter. The receiver shows -115.4 dBm sensitivity, a 4.0-dB noise figure, and a dynamic range of 80-dB with 396-mW power consumption.     

宽带射频功放晶体管非线性输出电容研究

分析了GaN(氮化镓)HEMT(高电子迁移率晶体管)非线性输出电容Cout与宽带功放效率的关系。通过建立非线性电路模型分析得出,利用Cout控制漏极端电压电流波形能减轻对谐波阻抗的精确要求,使高效率阻抗区域扩大化,从而使宽带功放匹配变为可能。选用GaN HEMT器件设计2~3 GHz频段射频功率放大器,实测结果为该放大器最高漏极效率(DE)为81.7%,功率附加效率(PAE)78.3%,功率为40.75 dBm。在1 GHz带宽内PAE也可达65%以上。实测结果验证了原理分析的可靠性,提出的方法不仅可用于宽带GaN功率放大器设计,对其他类型的微波功放设计同样有借鉴作用。     

Adaptive Digital Feedback Predistortion Technique for Linearizing Power Amplifiers

We have developed a new adaptive digital predistortion (DPD) linearization technique based on analog feedback predistortion (FBPD). The lookup-table-based feedback input can remove the bandwidth limitation of the feedback circuit related to the loop delay, and suppress feedback oscillation by accurate digital control of the feedback signal. Moreover, the predistortion (PD) signal can be extracted very efficiently. By combining the feedback linearization and DPD linearization techniques, the performance of the predistorter is enhanced significantly compared to the conventional DPD. To clearly visualize the characteristics of digital FBPD (DFBPD), we have compared it to the conventional DPD based on the recursive least square algorithm using Matlab simulation. The results clearly show that the new method is a good linearization algorithm, better than a conventional DPD. For the demonstration, a Doherty power amplifier with 180-W peak envelope power is linearized using the proposed DFBPD. For a 2.14-GHz forward-link wideband code-division multiple-access signal, the adjacent channel leakage ratio at 2.5-MHz offset is -58 dBc, which is improved by 15 dB at an average output power of 43 dBm     

Effect of jammer power on the performance of adaptive arrays

The effect of jammer power on the performance of adaptive arrays is studied. It is shown that the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array is a function of jammer power. In the presence of a wide-band jammer, the output SINR of the array decreases with an increase in jammer power and eventually goes to zero. Unlike continuous wave (CW) jammers, a wide-band jammer does not go through power inversion. Instead, as the jammer power is increased, the interference-to-noise ratio (INR) at the array output shows oscillations. For large jammer power, the output INR increases with an increase in jammer power.     

Adaptive digital/RF predistortion using a nonuniform LUT indexing function with built-in dependence on the amplifier nonlinearity

This paper reports on an integrated adaptive digital/RF predistorter using a nonuniform spaced lookup table (LUT) and in-phase/quadrature (I/Q) RF vector multiplier (VM). The LUT contents are directly deduced from the baseband input and output signals of the power amplifier (PA). In addition, a new nonlinear indexing function of the predistortion LUT with built-in dependence on the PA nonlinearity is proposed. This function is made to be robust to the input signal statistics. A comparison of this new indexation method with conventional approaches, namely, power and logarithmic power indexation functions, is carried out. The superiority of the proposed scheme is demonstrated in particular for class-AB amplifiers where the gain of the PA varies over the whole input range of the drive signal. The measured output spectrum of a linearized 90-W peak lateral double-diffused metal-oxide-semiconductor PA reveals a significant reduction of the power emission at the adjacent channels of approximately 15 dB under IS95, single-carrier, and multicarrier wide-band code-division multiple-access signals. The experimental evaluation is carried out using an RF/digital predistorter prototype that mainly includes an envelope detector, a linear I/Q RF VM, field-programmable gate array and digital signal processor, and fast analog/digital and digital/analog converters.     

Exploiting low complex digital predistortion to improve wideband nonlinear satellite downlinks

With the increasing demand for higher data rate, increasing throughput requires wider bandwidth. Due to the nonlinear effect of power amplifier, severe nonlinear distortion effects will appear onboard satellite. Digital predistortion (DPD) scheme is usually employed to compensate for the distortions and memory effects introduced by traveling wave tube amplifier (TWTA) and output multiplexing filter (OMUX). In conventional predistorter, the signal loss of band‐limited feedback signal output through OMUX is usually ignored. Actually, it will affect the linear effect of TWTA. In order to solve the problem as to improve wideband nonlinear satellite downlink, this paper introduces a novel spectral extrapolation method based on deep neural network to recover the band‐limited feedback signal. On this basis, an advanced orthogonal matching pursuit algorithm is adopted in the nonlinear TWTA model construction to further reduce the DPD complexity. The proposed setup effectively compensates the distortions and is well suited for systems that generate data bits on satellites.     

高功率回旋行波管新型宽带输出窗的设计

首先利用场匹配理论和传输级联矩阵建立多层介质窗的普遍分析方法,对回旋行波管输出窗进行解析分析,在理论分析和数值计算的基础上得到回旋行波管宽带输出窗的结构和尺寸;然后利用三维高频分析软件HFSS进行仿真和验证.通过热分析和优化设计,在Ka波段获得了平均功率容量达到50 kW,反射系数小于-20 dB的带宽约为3.6 GHz的高性能新型宽带输出窗.冷测实验表明,冷测结果与数值计算结果较为吻合.     

基于神经网络的宽带激光熔覆熔池特征参数预测

为了实现宽带激光熔覆熔池特征的准确预测,从 而对激光熔覆工艺过程进行实时监测、评价及反馈 控制。通过宽带激光熔覆全因素工艺试验采集熔池特征参数样本数据,采用遗传算法优化BP 神经网络的 初始权值和初始阈值,建立激光熔覆工艺参数(激光功率、粉末厚度、扫描速度)与熔池特 征参数之间的 BP神经网络预测模型。利用训练集数据对所建立的神经网络进行训练,形成输入与输出之间 的映射关系, 并利用测试集数据对网络进行测试。试验结果表明,宽带激光熔覆熔池特征参数神经网络预 测模型具有很 高的精度。该神经网络预测模型对激光熔覆过程监测及熔覆层质量控制具有重要意义。     

数字预失真功放EVM特性分析与实验验证

推导了无线通信系统误差向量幅度(EVM)与邻道功率比(ACPR)指标的相互关系,得出了通过功放线性化改善ACPR使得系统EVM减小的结论。随后采用具备结构简单、处理速度快、实时性好等优点的查找表(LUT)方法设计数字预失真器(DPD),数字预失真器用FPGA方式实现。对该数字预失真器进行了仿真分析,验证了理论推导结论,最后给出DPD功率放大器试验测试数据,与仿真结果吻合良好。     

A wide-band propagation model based on UTD for cellular mobileradio communications

The present wide-band propagation model based on uniform geometrical theory of diffraction (UTD) for cellular mobile radio communications includes two major contributions. First, a UTD-based narrow-band channel transfer function containing both the diffracted electric field and the reflection of diffracted electric fields is derived. Not only is it an important element of the wide-band modeling method, but it also leads to a total path-loss prediction model verified by comparisons with previously published theoretical and experimental results. In particular, the distance for horizontal placement on the street allows one to calculate the ray-path length difference (used in wide-band modeling) for the diffracted field and the reflection. Second, new refinements (including a number of explicit-form expressions to an existing method experimentally confirmed, simulating wide-band radiowave propagation for rural environments including terrain profiles) are added, making it applicable here. The method generates the time-domain path loss, wide-band path loss, and the relative power in the frequency domain. The time-domain path loss physically interprets and reasonably predicts the power delay profiles. The presence of this and similar power delay profiles, as well as the behavior of the relative power in the frequency domain, has been confirmed by existing wide-band propagation measurements. The value of the wide-band path loss is of the order of the total path loss at the carrier frequency     

A low-power high-performance digital predistorter for wideband power amplifiers

In this paper, we present a low-power high-performance digital predistorter (DPD) for the linearization of wideband RF power amplifiers (PAs). It is based on the novel FIR memory polynomial (FIR-MP) predistorter model, which significantly augments the performance of the conventional memory polynomial predistorter with the use of complex baseband digital FIR filter prior to the memory polynomial. The adjacent channel leakage ratio (ACLR) performance comparison between the conventional MP and the proposed FIR-MP is done based on simulations with multi-carrier modulated signals of 20 and 80 MHz bandwidths. The PA models used for the simulations are extracted from the measurements of a commercial \(1\,\hbox {W}\) GaAs HBT PA. At the ideal system-level simulations, the improvements in ACLR over the conventional MP are 7.2  and 15.6 dB, respectively, for 20 and 80 MHz signals. The choice of selection of various parameters of the predistorter along with the subsequent digital-to-analog converter (DAC) is presented. The impact of fixed-point representation is assessed using ACLR metrics, which shows that a wordlength of 14 bits is sufficient to obtain ACLR beyond \(45\,\hbox {dBc}\) with a margin of \(10\,\hbox {dB}\). The proposed predistorter is synthesized in \(28\,\hbox {nm}\) fully-depleted silicon-on-insulator (FDSOI) CMOS process. It is shown that with a fraction of the power and die area of that of the MP a huge improvement in ACLR is attained. With an overall power consumption of 8.2 and 88.8 mW, respectively, for 20 and 80 MHz signals, the FIR-MP DPD proves to be a suitable candidate for small-cell base station PA linearization.     

Monolithic MESFET distributed baluns based on the distributedamplifier gate-line termination technique

The principles of the distributed amplifier are applied to realize wide-band monolithic distributed baluns. The technique reported here is based on using the gate-line “termination” of a distributed amplifier topology as the noninverting output and the inherent phase inversion property of the metal-semiconductor field-effect transistor (MESFET) to provide the antiphase output from the drain-line. Closed-form expressions are derived for the two output voltage signals and their respective power gains. The theoretical performance of the balun is then examined as a function of the important MESFET parameters and other circuit parameters. Some practical design considerations are given followed by the measured results of two monolithic prototypes. The first is a basic two-section balun, while the second employs a four-section balun with a three-stage positive gain slope preamplifier to compensate for the increase in gate-line loss with frequency. Balun operation over 0.5-20 GHz and 0.5-12 GHz has been demonstrated for the two-section and four-section balun, respectively     

On The Sensitivity of RF Transmitters' Memory Polynomial Model Identification to Delay Alignment Resolution

In this letter, the effects of delay alignment between the input and output baseband waveforms on the performance of a radio frequency transmitters' memory polynomial based model are studied. A 100-W average power transmitter is characterized; various delay values are applied to align the input and output data; and, a model is derived for each delay value. The models' performances, evaluated for these delay values both in time and frequency domains, demonstrate that the memory polynomial model is sensitive to delay overestimation but not to delay underestimation. It is established that a delay underestimation by up to one sampling period does not affect the performance of the identified model. This overcomes the need for the signal oversampling required for high-resolution delay alignment. Consequently, the computational complexity of the digital signal processing algorithm employed for delay estimation and alignment is considerably reduced.     

基于偏最小二乘的低复杂度数字预失真

在宽带场景下,传统的数字预失真(DPD)模型需要更高的阶次和更多的系数来校正功率放大器(PA)强非线性和记忆效应,这就会导致极高的计算复杂度和解算系数时的病态问题.文章围绕复杂DPD模型参数辨识和低复杂度DPD算法实现展开深入研究,提出了一种新的基于偏最小二乘(PLS)的低复杂度DPD方法.所提方法根据PA的前逆输入输...