数字发射机A/D(模数)转换技术研究

我们知道数字调幅(DAM)中波发射机里包含有A/D(模数)转换电路,其主要功能是实现时间上连续模拟信号向时间上离散数字信号的转换。经过A/D转换以后的数字信号就可以进行调制编码,从而实现对射频功放的控制,同时使"数字幅度调制"形成。再经过D/A(数模)转换实现数字信号向模拟信号的转换。该技术的应用,能够使数字调幅(DAM)中波发射机取得最佳音频效果。     

自适应前馈射频功率放大器设计

在高功率射频放大器设计时，通常采用前馈技术来改善宽带信号的线性度。本文基于普通的前馈系统。提出了一种新的自适应前馈线性化技术，并结合信号包络检测技术进行带外信号调节。同时，还利用该技术在计算机仿真系统上设计了一个射频功率放大器的功放输出级，通过对仿真结果的比较，发现他能显著改善IMD性能。     

DVB—S简介（十一）

从图中可以看出,发射端的基带成形滤波器,接收端的匹配成形滤波器使信道的通频带具有带限特性;而发射设备中的高功放(HPA)和卫星转发器上的行波管放大器(TWTA)都是非线性器件,即其输入输出特性曲线是非线性的,且具有调幅调相(AM/PM)转换特性,也就是说当输入的射频载波幅度发生变化时,会引起输出载波相位变化,从而引起互调噪声,使比特误码率恶化,并改变发射信号的射频频谱形状。C波段卫星信道的自由空间部分的参数特性基本上是恒定的,没有起伏衰落现象,     

Ka频段10 W自适应射频预失真线性化固态功放研制

射频功率放大器的特性会随信道切换、环境温度、工作状态等多种因素发生变化,为了保证功率放大器的优良工作特性,具有自适应性能的预失真系统就显得非常重要。提出了一种自适应反馈检测方法,以减小放大器输出信号的幅度失真和相位失真作为系统自适应的优化目标,采用多方向搜索优化算法对预失真系统进行优化调整,使系统始终处于最优工作状态。研制了工作于Ka频段10 W自适应射频预失真线性化固态功放原理样机,当工作温度为-40℃~+60℃时,在3 GHz的工作带宽内,三阶交调指标优于-32 dBc。测试结果表明该功放具有工作频带宽、温度适应性广等特点。     

数字调幅发射机调制原理分析

数字调幅发射机把“音频+直流+抖动”的模拟信号转换成12 bit的数字信号去控制各个功放模块的开关状态，运用的数字调制技术包括模数（Analog/Digital,A/D）转换和数模（Digital/Analog,D/A）转换。基于此，介绍数字调制原理，并对转换错误问题进行分析和处理。     

D类MOSFET在发射机射频功放中的应用

分析了MOSFET的开关特性，阐述了D类MOSFET在数字化调幅发射机射频功放电路中的应用方法，并对MOSFET的维护和测试进行了说明。     

基于0.7 μm InP DHBT的毫米波数字化功率放大器

基于磷化铟双异质结双极型晶体管(InP DHBT)实现了一款K波段数字化功率放大器芯片.该芯片利用InP DHBT工艺兼容高速数字与射频功率电路的优点,采用多个数字功放单元并联连接的形式,每个数字功放单元可以根据数字基带控制信号接通或断开,形成多位的射频功率直接输出.在分析了基于共射-共基结构数字功放单元电路的瞬态响应...     

ET功放的自适应时延估计算法研究

为了保证包络跟踪(ET)功放的性能,需要实现射频支路和包络支路信号的严格同步。基于仿真分析恒定增益下功放输入信号功率与漏极电压间的关系,设计了一种基于时延失真方差的自适应时延估计算法,并通过仿真验证分析了算法性能。仿真结果表明,通过设计合适的迭代时延向量,算法能够实现对ET功放支路时延差的准确估计。     

基于矢网的行波管AM/PM转换系数的测试

分别用传统测试方法和用矢网测量S参数法测试了行波管的调幅调相转换系数,对两次测试结果进行了比较,并重点对矢网测试的误差进行了分析和讨论,确定了用矢网测量行波管AM/PM参量的方法.实际测试结果表明通过调整状态设置参量,用矢网测试行波管AM/PM参量的方法是高效可行的.     

包络跟踪电源优化设计与仿真

在移动通信3G/4G网络中,包络跟踪技术是提高射频功放效率的核心技术之一。从包络跟踪的相位失真问题入手,以降压变换器为拓扑,提出了以4阶贝塞尔低通滤波器传递函数为整体设计模型的包络跟踪电源设计方法,通过线性补偿控制实现对包络跟踪电源的控制。同时,依据线性控制单元在实际设计中可能遇到的问题,提出了一种更为适合实际应用的线性控制器设计方法。最后,通过软件Pspice对此包络跟踪电源进行仿真验证,以降带宽处理后的单载波1 MHz信道宽度的WCDMA包络信号作为跟踪参考信号,通过软件matlab的simulink仿真对包络跟踪电源进行验证,证明方案实际应用可行。     

WCDMA功放预失真发生器的研究

针对宽带码分多址(WCDMA)功放的非线性失真问题,提出了一种简单有效的解决方案,即通过预失真发生器对幅度-幅度(AM-AM)及幅度-相位(AM-PM)曲线进行调整,以补偿功放的非线性失真.这种方案主要是通过利用二极管的非线性特性设计出的预失真发生器来实现的.实验证明,将预失真发生器与WCDMA功放配合使用,能将功放的邻道功率泄漏比(ACPR)改善5 dB.     

Analysis and Design of a Dynamic Predistorter for WCDMA Handset Power Amplifiers

This paper presents a dynamic predistorter (PD), which linearizes the dynamic AM-AM and AM-PM of a wideband code division multiple access handset power amplifier (PA). The dynamic PD allows an adjacent channel leakage power ratio (ACPR) improvement of 15.7 dB, which is superior to conventional PDs that linearize static AM-AM and AM-PM. The dynamic PD was designed using an HBT generating nonlinearity, a short circuit at the baseband (les4 MHz), and a load circuit for the HBT at the RF fundamental band (ap1.95 GHz). Volterra-series analysis was performed to understand the mechanism of the dynamic PD. The analysis revealed that the short circuit at the baseband enabled the dynamic PD generating third-order intermodulation distortion (IMD3) with opposite phase to the fundamental tone (i.e., antiphase IMD3). The antiphase IMD3 allows dynamic gain compression, which linearizes the dynamic gain expansion of a PA with low quiescent current. The analysis also revealed that the IMD3 amplitude of the dynamic PD can be adjusted by load impedance at the RF fundamental band, which enables the gradient of dynamic AM-AM and AM-PM to be optimized to linearize the PA. The fabricated two-stage InGaP/GaAs HBT PA module with the dynamic PD exhibited an ACPR of -40 dBc and a power-added efficiency of 50% at an average output power of 26.8 dBm with a quiescent current of 20 mA     

宽带CDMA信号激励下的功放性能分析

根据功放的实测AM－AM、AM－PM特性,采用时域分析方法,并应用带通非线性理论和数字信号处理技术,分析了宽带数字调制信号激励下 的射频功率放大器非线性失真特性。     

A Compact High-Efficiency CMOS Power Amplifier With Built-in Linearizer

In this letter, a compact high-efficiency CMOS power amplifier (PA) with built-in linearizer that works at 2.4 GHz using TSMC 0.18 $mu$m technology for digital wireless communications applications is presented. The cascode configuration is utilized to overcome the low break-down voltage problem and the hot-carrier effects for high power operations of CMOS devices. The linearizer design reduces the AM-AM quantities to extend the $P_{1 {rm dB}}$ point while the AM-PM distortions are improved as well. The final designed PA exhibits $P_{1 {rm dB}}$ of 20.6 dBm and 24.6% power-added-efficiency (PAE) with 35 dBm output-intercept-point in the third order (OIP3). The saturated output power is 22 dBm with 30% in PAE, while the chip size is less than 1 mm$^{2}$.      

LDMOS线性微波功率放大器设计

LDMOS以其大功率、高线性度和高效率等优点得到广泛的应用.采用2-tone负载牵引法得到了LDMOS晶体管MRF18030的输入和输出阻抗.在对晶体管绝对稳定性分析的基础上,运用共轭匹配法设计出匹配网络,并将匹配网络转化为MOMENTUM元件运用在电路设计中,大大提高了设计的准确性.采用载波复幂级数法对PA的AM-AM和AM-PM非线性特性进行了准确计算,弥补了传统泰勒级数只能分析AM-AM的不足.得到了用来消除PA非线性的反载波复幂级数.根据所得反载波复幂级数,利用二极管非线性特性设计出一种新的结构简单、易于实现的预失真器,给出其准确的电路模型表达式,得到了幅值、角度等参数的精确值.ADS仿真结果表明,IMD3改善了27dB.最终,成功设计出大功率、高效率、高线性的LDMOS微波功率放大器.     

A new unequal three-tone signal method for AM-AM and AM-PMdistortion measurements suitable for characterization of satellitecommunication transmitters/transponders

A new method for characterization of AM-AM and AM-PM distortion of power amplifiers (PAs) using only power measurements is proposed in this paper This technique was found to be suitable for the characterization of satellite communication transmitters/transponders. It consists of using an unequal three-tone signal (UTTS) to drive either the base-station PA's transmitter or the satellite transponder's PA and to measure the level of this UTTS at the output of the transmitter/transponder. By comparison of the three tone levels at the input and output of the transmitter/transponder, one can calculate the AM-AM compression factor and AM-PM conversion coefficient of the transmitter/transponder PA using closed-form expressions     

An analytic approach for CDMA output of feedforward power amplifier

In this paper, a novel method is introduced to predict the Code-Division Multiple-Access (CDMA) output spectrum of an RF power amplifier linearized with feedforward technique based on transfer function. In this method, an RF power amplifier is modeled mathematically by nonlinear complex envelope transfer function based on AM-AM and AM-PM distortion diagrams. Using this model, analytic expressions of CDMA output spectrum of power amplifier is calculated. Having mathematical model of RF power amplifier leads to derive analytic expressions for InterModulation (IM) products in feedforward amplifier. Based on these expressions, IM products are related to nonlinear complex envelope transfer function of feedforward amplifier. Then, CDMA output spectrum of feedforward linearization technique is predicted. The loops imbalances in feedforward technique are considered in analysis. Finally, the results of derived expressions in MATLAB software are compared with ADS simulations results and good agreements were achieved. Employing this method gives insight for feedforward analysis and loops imbalances effects in feedforward amplifier for CDMA applications.     

基于Saleh函数的RF功率放大器正交非线性带通模型

提出了一种基于Saleh函数的RF功率放大器正交非线性带通模型。通过将RF功率放大器的幅度、相位非线性失真转换为两个不存在相位失真而只有幅度失真的正交并行信道,并用Saleh函数对两正交信道的幅度失真进行了逼近,与基于Taylor级数的RF功率放大器正交非线性带通模型相比较,新模型具有更好的逼近精度。     

A vector intermodulation analyzer applied to behavioral modeling of nonlinear amplifiers with memory

A large signal vector intermodulation network analyzer with a dynamic range of 90 dB and phase resolution of better than 2/spl deg/ is reported. The analyzer is used in conjunction with a multislice behavioral model to characterize memory effects in three different RF power amplifiers: an MOSFET instrumentation amplifier, a multistage GaAs/silicon-based broadband microwave integrated-circuit amplifier, and an SiGe HBT monolithic-microwave integrated-circuit amplifier. The multislice behavioral model architecture builds on conventional single-tone AM-AM and AM-PM modeling extended to capture long-term memory effects that are characterized by asymmetric intermodulation distortion (IMD). Phase asymmetries of upper and lower IMD are captured. A systematic procedure for extracting the model is presented.     

WCDMA系统中基于查找表的预失真技术的研究

在无线通信系统中,高功率放大器因其非线性,导致AM／PM效应使得微分相位、微分增益和互调失真变坏。高质量的通信系统设计应尽可能减小功率放大器的AM／PM效应。因此,针对宽带码分多址（WCDMA）功放非线性失真问题,采用一种基于查找表（LUT）的自适应预失真方法,改善功放的非线性失真。仿真表明．该方法能有效补偿放大器产生的AM—AM、AM-PM失真,并将功放的邻道功率泄漏比（ACPR）改善到30dB左右。