Quantifying memory effects in RF power amplifiers

This paper proposes a system-level behavioral model for RF power amplifiers (PAs), which exhibit memory effects, that is based on the parallel Wiener system. The model extraction is performed using two-tone intermodulation distortion (IMD) measurements with different tone frequency spacings and power levels. It is found that by using such a model, more accurate adjacent-channel power-ratio levels may be predicted for high PAS close to the carrier frequency. This is validated using IS-95B CDMA signals on a low-power (0.5 W) class-AB PA, and on a high-power (45 W) class-B PA. The model also provides a means to quantify memory effects in terms of a figure-of-merit that calculates the relative contribution to the IMD of the memoryless and memory portion of the PA nonlinearity. This figure-of-merit is useful in providing an estimate of the amount of correction that a memoryless predistortion system may have on PAS that exhibit memory effects.     

Adaptive predistortion with reduced feedback complexity [RF poweramplifiers]

A technique for the adaption of a complex-gain baseband predistorter is proposed, using only a single coherent downconversion in the feedback path. Despite this reduction in complexity when compared to previous implementations, the adaption process can still correct for both AM/AM and AM/PM nonlinearities in the RF power amplifier. Practical results from a 220 MHz transmitter are given     

Measurement and simulation of memory effects in predistortionlinearizers

Detrimental effects of memories in linearizers are described, and two efficient techniques are presented to measure them. These techniques allow a real-time adjustment and correction of the linearizer and/or amplifier circuits and an overall improvement of the intermodulation performance over a wide envelope frequency band. This is especially important for broadband applications, where high efficiency and linearity are required, and where memory effects, if not detected and properly corrected, may significantly degrade the system's performance. Experimental results for a 20-W linearized L-band power amplifier are presented to illustrate the effects of memory. The two techniques-a dynamic AM/AM and AM/PM measurement system and a pulse power measurement system-are described. A simulation approach that can be used to predict the influence of memory effects in practical systems is illustrated for nonlinear amplifiers. Adaptive linearization techniques are discussed     

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.     

A predistortion linearizer using envelope-feedback technique withsimplified carrier cancellation scheme for class-A and class-AB poweramplifiers

A predistortion linearization method using an envelope-feedback technique is proposed and implemented in this paper. This linearizer compensates the gain and phase nonlinearity of power amplifier (PA) simultaneously by controlling both variable attenuator and phase shifter with the feedback of only the difference signal between input and output envelopes. A new carrier cancellation scheme composed of a minimization circuit, log detector, and vector modulator is also presented. This circuit achieves adaptive control of the linearizer by enabling direct measurement of out-of-band power. It is well suited to a multichannel system where the allocated channels are time variant. The principle of the proposed linearizer is described and simple AM-AM distortion analysis is presented analytically and graphically based on the conceptual schematic diagram. A two-tone test for a class-A PA at 1.855 GHz with frequency spacing of 1 MHz showed intermodulation-distortion reduction of maximum 16 dB and stable operation over 5-dB output power variation up to 4-dB backoff from the saturation power level. The proposed linearizer is also applicable to class-AB PA's without further special adjustments. The adaptation circuit is fully implemented with analog integrated circuits, which can further extend its applicability with the integration technology     

A simple method for characterizing the RF properties of high-temperature superconductive materials

A simple method using a resonant strip in a rectangular waveguide has been devised for superconductive material characterization. The method has the advantages of simplicity; and it requires only a small piece of the superconductive material. The resonant frequency of the superconductive strip can be predicted theoretically.     

Thermal memory effects modeling and compensation in RF power amplifiers and predistortion linearizers

Memory effects, which influence the performance of RF power amplifiers (PAs) and predistortion-based linearizers, become more significant and critical in designing these circuits as the modulation signal bandwidth and operation power increase. This paper reports on an attempt to investigate, model, and quantify the contributions of the electrical nonlinearity effects and the thermal memory effects to a PA's distortion generation, as well as how to compensate for these effects in designing baseband predistortion schemes. The first part of this paper reports on the development of an accurate dynamic expression of the instantaneous junction temperature as a function of the instantaneous dissipated power. This expression has been used in the construction of an electrothermal model for the PA. Parameters for the new proposed behavior model were determined from the PA measurements obtained under different excitation conditions (e.g., small-signal and pulsed RF tests). This study led us to conclude that the effects of the transistor self-heating phenomenon are more important under narrow-band signal (e.g., enhanced data for global evolution of global system for mobile communications) than for signals with wide modulation bandwidth (CDMA2000, Universal Mobile Telecommunications System). In the second part of this paper, the newly developed model has also been used to design a temperature-compensated predistortion function to compensate for these effects. The linearized PA output spectrum and error vector magnitude show a significant performance improvement in the temperature-compensated predistortion function over a memoryless predistortion. The results of these measurements that have been conducted on a 90-W peak lateral double-diffused metal-oxide-semiconductor PA are in agreement with those obtained from simulations using the developed PA and the predistorter models implemented in an ADS environment.     

A data optimization test technique for characterizing embedded ADCs

A novel data optimization test technique is presented which utilizes a BIST structure, an ADC model and histogram data to characterize embedded ADCs. A practical 8 bit ADC is modeled and then characterized using 20% less data points then conventional analysis with a 78% reduction in the amount of data required to be shifted off-chip. Comparisons between theoretical, modeled and practical results are also made in the paper.     

An improved look-up table predistortion technique for HPA with memory effects in OFDM systems

It is well known that HPAs (High Power Amplifiers) are inherently nonlinear devices and many researches have focused on the predistortion for memoryless HPAs. However, memory effects of HPAs can no longer be ignored when communication systems have wider bandwidth. Memoryless predistortion techniques proposed previously seldom have satisfactory effectiveness for typical wideband applications such as OFDM (Orthogonal Frequency Division Multiplexing) systems. In this paper, an improved adaptive predistortion method called 2D LUT (2-dimension look-up table) with different accuracy levels is presented to linearize HPAs with memory effects. Simulation and experimental results show that 2D LUT implements excellent performance in mitigating the signal deterioration caused by memory effects, both rectifies the signal constellation distortion and suppresses the spectrum emission. Large scale matrix computation is also avoidable in these adaptive algorithms, which makes them feasible when a real-time system is necessary.     

军用电台射频性能的三维测试

射频测试是电台性能测试的一项基本内容.本文将已经标准化了的手机与无线局域网的射频测试内容和方法引入军用电台的射频性能测试中,定量地考察了电台的辐射性能.并提出该方法同样适用于我军的高速数据电台.     

A new technique for RF measurements using superconductors

The quantization of magnetic flux in a superconducting circuit can serve for the measurement of electrical quantities in the same way that we use the wavelength of light to measure length. We report a demonstration of this function in the measurement of attenuation ratio at a frequency of 30 MHz.     

一种去嵌入射频测量技术

去嵌入是一种射频微波精确测量技术。本文介绍了一种新型的去嵌入测量技术。该方法只需要一个对称的直通微带结构就能完成去嵌入。最后利用该方法对0603封装的电感进行了测量,并提取了精确测量后的电感模型。结果表明本去嵌入方法可以应用于射频PCB上器件模型的精确测量和模型提取。     

不断增强RF功率测量

精确的RF功率管理是现代无线发射器的热点话题,从基站的功率放大器保护到移动应用中的延长电池使用时间,它都有很多的优点。RF功率监测器,比如对数放大器,允许RF功率测量系统在一个较宽的范围监控和动态调整发射功率。尽管近几年来功率监测的精度已经有了很大改进,但是对于像那些需要高功率发射的应用甚至受到0dB功率监测误差微小变化引起的显著影响。因此这也促使检测器性能不断提高。     

A technique for characterizing surface recombination in silicon wafers based on thermal-emission measurements

A noncontact technique for the measurement of the surface-recombination rate in silicon wafers is suggested. A wafer under study is excited optically in the spectral region of intrinsic absorption, and the excitation-wavelength dependence of the power of the wafer thermal emission beyond the intrinsic-absorption edge is examined. The surface-recombination rate is determined from the ratio of intensities of the wafer thermal emission in the wavelength range 3–5 μm recorded under excitation with two laser diodes with wavelengths of 863 and 966 nm. Wafers subjected to different surface treatments were tested; at 230°C, rates on the order of 10⁴ cm/s were measured after mechanical polishing and 10³ cm/s after etching in CP-4A etchant. The applicability of the method is discussed, and the measurement error as a function of the wafer and light-source parameters is considered.     

射频吸波材料波导测试法装置的仿真分析

射频吸波材料在电磁兼容(EMC)领域有着广泛的应用,密闭波导测试法是吸波材料性能测试的重要手段,适用于500MHz-1GHz频率范围,具有所需试样数目较少的优点.本文介绍了波导法的基本原理和实验室设计完成的波导法装置结构,并对影响波导法装置性能的因素进行仿真分析,在分析的基础上优化结构设计.     

射频功率放大器自适应预失真技术研究

本文研究了一种用于改善射频功率放大器非线性失真的预失真技术.首先,对预失真技术的原理进行了简单的论述,随后,给出了谐波发生器的电路结构,并对其特性进行了分析,在此基础上添加了自适应控制电路,并对其进行了深入的算法推导,通过与自适应技术的结合,整个系统的稳定性得到提高.将此预失真线性化电路用于射频放大器中,IMD3的性能...     

Measurement technique for narrow-linewidth ferrimagnets

This proposed technique for narrow-linewidth measurement allows one to take into account the radiation-damping contribution to the observed linewidth. Therefore it is possible, considering this important interaction between the sample and circuit, to increase the measurement sensitivity and accuracy.     

A gain stabilization technique for tuned RF low-noise amplifiers

A gain stabilization technique for tuned integrated low-noise amplifiers (LNAs) is presented. The proposed method regulates the LC-tuned load impedance of the amplifier at the operation frequency against variations of passive devices in integrated circuit (IC) process. The impedance stabilization technique is based on the excellent relative accuracy of integrated resistors. Although the absolute deviation of the integrated resistors can be as large as /spl plusmn/20%, the relative deviation can be made smaller than /spl plusmn/1% provided that resistors are placed close to each other. By applying the proposed method, the voltage-gain variation of the inductively degenerated common-source LNA, which is the most popular LNA architecture, can be reduced several decibels. As a consequence, the entire radio receiver can more easily meet its specifications in the presence of IC process variations and the product yield is improved. Finally, besides the LNAs, the presented stabilization technique can also be utilized in other tuned amplifiers, filters or oscillators employing damped LC-tuned loads.     

A fast computational technique for RF window in millimeter wave tubes

RF Window of millimeter wave tubes becomes very thin because of extreme high frequency, so that power capacity of the window is limited, manufacturing is difficult and it easy leaks. The equivalent circuit and computation are given for a type of ceramic block RF window with compensating irises. This RF window has higher power capacity, compact mechanical strength, easy manufacturing and airtight welding. The testing results show that the design method is fast and useful accuracy.     

数字射频存贮器（DRFM）在雷达和电子战系统中的应用

本文简要地介绍了数字射频存贮器(DRFM)的基本功能和主要技术指标,然后较详细地列举了它在雷达和电子战系统中的一些典型应用。