一种噪声系数低,功率匹配好的1.1千兆赫到2.4千兆赫的晶体管放大器

目前已制造了一种有潜力的低成本放大器微型组件。放大器是采用晶体管管芯和薄膜、梁式引线或片状元件等构成的混合微波集成电路。这种放大器的设计表明,已经有一种能够获得最低噪声系数的输入功率匹配技术。这种技术是使用反馈的方法实现功率匹配,而同时在晶体管的输入端保持最小噪声系数所要求的源阻抗。放大器采用Mullard公司生产的BFR90晶体管管芯,在无反馈时,放大器的失配电压驻波比大于3:1。在1.5千兆赫的中心频率,300兆赫的宽带范围内,对50欧姆的源,放大器的噪声系数已可做到3.5分贝,输入电压驻波比小于1.25:1。在1.1至2.4千兆赫的频率范围,两级匹配放大器的增益在16分贝与12分贝之间。     

快速设计参考图表

在测量一个放大器的噪声系数时,往往需要在被测器件与衰减器之间插入一放大级。因此,测得的噪声系数是两个放大器级联的总噪声系数。当第一级放大器的增益和第二级放大器的噪声系数为已知值时,利用图1的列线图便可确定第一级放大器的噪声系数。列线图的使用步骤1.将F_(1-2)(测得的总噪声系数) 和G_1(第一级的增益)相连并与a相交于一点;     

噪声影响及计算变换图表

嗓声-温度的计算1.修正第二级噪声系数列线图在测量一个放大器的噪声系数时,往往需要在被测器件与衰减器之间插入附加增益.因此,测得的噪声系数是该级联的总噪声系数.当它的增益和第二级放大器的噪声系数已知值时,利用图1的列线图便可确定第一级放大器的噪声系数.     

基于噪声抵消技术的低功耗C频段差分低噪声放大器

设计了一款??基于噪声抵消技术的低功耗C频段的差分低噪声放大器。该放大器由输入级、放大级以及输出缓冲级3个模块构成,其中输入级采用电容交叉耦合的差分对与直接交叉耦合结构差分对级联,实现输入匹配及噪声抵消;放大级采用具有电阻-电感并联反馈的电流复用结构来获得高的增益、良好的增益平坦性及低的功耗;输出缓冲级采用源跟随器结构,实现良好的输出匹配。基于TSMC 0.18 μm CMOS工艺库,验证表明在C频段,放大器的增益为20.4??0.5 dB,噪声系数介于2.3~2.4 dB之间,输入和输出的回波损耗均优于-11 dB,稳定因子恒大于1,在6.5 GHz下,1 dB压缩点为-16.6 dBm,IIP3为-7 dBm,在2.5 V电压下,电路功耗仅为6.75 mW。     

单电源测量放大器

ＯＰ2 8 4是一种低噪声双运算放大器 ,带宽为 4ＭＨｚ且为真实的 (ｒａｉｌ -ｔｏ -ｒａｉｌ)输入 输出运算。这些特性使其非常适用于低电源电压 ,如用于该图所示的 2个运算放大器测量放大器。该电路采用传统的 2个运算放大器测量拓扑结构 ,用 4个电阻器设置增益。该电路的转换方程与非变换放大器相同。电阻器Ｒ2 与Ｒ3 应该互相匹配 ,而且 (Ｒ1 +Ｐ1 )也应与Ｒ4匹配 ,保证较好的共模抑制(ＣＭＲ)性能。建议Ｒ2 和Ｒ3 采用电阻器网络 ,因为这样可得到必要的相对容差匹配。利用电压计Ｐ1 调节直流ＣＭＲ ,使其最佳 ,而用电容器Ｃ1 使交流Ｃ…     

基于EDFA+FRA的增益平坦补偿

采用光子转换理论和数值分析方法，研究了采用DCF光纤的喇曼放大器和掺铒光纤放大器组成的混合放大器在DWDM系统中的应用。通过对喇曼光纤放大器的光纤长度、泵浦功率的选择，使得混合放大器的总增益达到一定的平坦度；并分析设计了增益均衡器，让混合放大器最后的总增益达到更高的平坦度。     

基于ADS仿真的宽带低噪声放大器设计

设计了一个S频段宽带低噪声放大器.该放大器采用两级E-PHEMT晶体管(ATF541M4)级联结构,单电源供电模式.应用微波仿真软件ADS对匹配电路进行了优化设计,最后通过S参数及谐波平衡仿真得到放大器的各项性能参数,在2.7～3.1 GHz频率范围内噪声系数小于0.6 dB,带内增益大于30 dB,带内平坦度小于±1 dB,输入输出驻波比小于1.6 dB,1 dB增益压缩点输入功率不小于-15 dBm.仿真结果表明,该设计完全满足性能指标要求.     

实用电路

1.用于非反相运算放大器的零增益模块电子学教科书通常会告诉你,非反相的运算放大器正常情况下不能被调节至0dB增益。如果需要零输出,通常需要使用一个反相放大器和一个放置在其前面的缓冲放大器,由缓冲放大器来充当增加阻抗的装置。右边的电路图示出了实现非反相放大器始终降为零输出的小技巧。其窍门就在于连接了一个线性律的立体电位计,因此当主轴被顺时针拨动时,P1a中的电阻就增加(增益上升),与此同时P1b的接触电刷就朝着运算放大器输出的方向移动(信号更多)。当接触电刷被逆时针拨动时,P1a的电阻就降低,也同时降低增益,而此时P1b向负…     

ISM频段射频放大的小信号分析

为解决ISM频段小信号放大器降低失配与减小噪声之间的矛盾,提出了一种改善放大 器性能的分析方法,满足信源、晶体管与负载三者之间的失配程度在受限条件下增益和噪声 的最优化。指出增益、驻波比和噪声多个性能参数不能同时达到最优,提出了提高射频放大 器综合性能的方法。在24 GHz的ISM频段进行的仿真结果表明,驻波比越小,增益越 大,噪声系数受失配限制的影响,在满足增益的条件下失配受限会使噪声系数增大。     

带二级密勒补偿的运算放大器研究

介绍了带二级密勒补偿的运算放大器的电路原理和分析方法,同时设计了一个二级运放并得到了仿真结果,仿真结果表明补偿电路提高了放大器的增益带宽,设计的电路功耗较低,负载较大。     

Responsible Marketing: Can Social Enterprises Show the Way?

In this article, the authors present a new perspective on responsible marketing. We discuss if and how social enterprises can present a new understanding of responsible marketing. Relevant publications (14 on social entrepreneurship, 40 on marketing in non-profit organizations and social enterprises and 41 papers on marketing) are selected and reviewed. The result of the literature analysis and synthesis show that social enterprises can gain from a more formal, systematic approach to marketing. Since social enterprises prioritize social goals over business results, successful adoption of marketing policies and practices can help then create a blueprint for responsible marketing. Marketing of socially relevant products and services by social enterprises thus create a new paradigm of responsible marketing. Such models can also be useful for larger corporations who look at social business and shared value creation as part of their business and marketing strategy.     

团队成员视角下个体地位获得事件对同事行为的影响：基于事件系统理论和社会比较理论

文章旨在全面揭示个体地位获得事件对团队成员认知和行为的影响路径，以及在何种条件下个体地位获得事件将促进团队成员的积极行为表现，进而为管理策略的提出提供理论依据。通过对来自28个团队的293名员工进行问卷调查，并运用结构方程模型进行数据分析，结果表明：个体地位获得事件通过团队成员资源收益/威胁感知的中介作用分别对团队成员人际帮助行为和人际回避行为产生正向影响，团队合作氛围负向调节个体地位获得事件与资源威胁感知的关系，并对个体地位获得事件与团队成员人际帮助行为的关系具有显著的有调节中介作用。研究结果不仅进一步拓展了个体地位获得事件对员工行为的影响研究，而且揭示了个体地位获得事件对员工行为的影响机制和边界条件。     

将射频放大器噪声系数减至最小的基本技术与方法

低噪声微波晶体管通常要求具有最小的噪声系数及相应的增益(一般O.5～1.5分贝,小于晶体管的最大有效增益).这可通过调节放大器,牺牲一点噪声系数来获得最佳的性能.     

基于网络编码的用户协作分集系统性能分析

针对非协作通信和传统协作通信系统不能达到高天线分集增益的问题,提出基于网络 编码的用户协作系统模型。研究了基于网络编码不同协作用户的天线分集增益,并分析非协 作机制、传统用户协作机制和基于网络编码用户协作机制的中断概率。理论分析和系统仿真 表明,基于网络编码的用户协作系统能显著降低系统中断概率,获得更大的分集增益,且协 作用户数越多,系统分集度越好。     

Continuity in the gains from trade with similar consumers

The conditions under which one can prove directly that all consumers gain from the elimination of prohibitive tariffs are very stringent. Yet it is intuitively plausible that if these conditions were ‘almost’ met, the results would still obtain and all would gain. We establish this rigorously by use of a topology on economic agents, as developed by Kannai, Debreu and Hildenbrand. Specifically, we show that if, in a given economy, all agents gain in going from autarky to free trade, then in any economies composed of agents sufficiently similar to those in the given one, all will gain.     

一种低截获卫星通信技术及其抗侦测性能分析

针对海上低截获通信应用,提出了一种低截获卫星通信技术并分析了其抗侦测性能。通过宽频带、低信息速率实现高增益扩频,系统设计上综合高工作频率、高增益天线等措施,降低卫星通信信号的功率谱密度;结合卫星链路计算,重点分析在同步轨道、低轨道电子侦察卫星侦测时的抗截获性能。理论分析和数值计算结果表明,增大扩频增益和天线增益可有效对抗同步轨道电子侦察卫星天线增益优势,对抗低轨道电子侦察卫星轨道优势,实现卫星低截获通信。     

Linking Entrepreneurship and Economic Growth

In the 1980s stagflation and high unemployment caused a renewed interest in supply side economics and in factors determining economic growth. Simultaneously, the 1980s and 1990s have seen a reevaluation of the role of small firms and a renewed attention for entrepreneurship. The goal of this survey is to synthesize disparate strands of literature to link entrepreneurship to economic growth. This will be done by investigating the relationship between entrepreneurship and economic growth using elements of various fields: historical views on entrepreneurship, macro-economic growth theory, industrial economics (Porter's competitive advantage of nations), evolutionary economics, history of economic growth (rise and fall of nations) and the management literature on large corporate organizations. Understanding the role of entrepreneurship in the process of economic growth requires the decomposition of the concept of entrepreneurship. A first part of our synthesis is to contribute to the understanding of the dimensions involved, while paying attention to the level of analysis (individual, firm and aggregate level). A second part is to gain insight in the causal links between these entrepreneurial dimensions and economic growth. A third part is to make suggestions for future empirical research into the relationship between (dimensions of) entrepreneurship and economic growth.     

Situational Moral Disengagement: Can the Effects of Self-Interest be Mitigated?

Self-interest has long been recognized as a powerful human motive. Yet, much remains to be understood about the thinking behind self-interested pursuits. Drawing from multiple literatures, we propose that situations high in opportunity for self-interested gain trigger a type of moral cognition called moral disengagement that allows the individual to more easily disengage internalized moral standards. We also theorize two countervailing forces—situational harm to others and dispositional conscientiousness—that may weaken the effects of personal gain on morally disengaged reasoning. We test our hypotheses in two studies using qualitative and quantitative data and complementary research methods and design. We demonstrate that when personal gain incentives are relatively moderate, reminders of harm to others can reduce the likelihood that employees will morally disengage. Furthermore, when strong personal gain incentives are present in a situation, highly conscientious individuals are less apt than their counterparts to engage in morally disengaged reasoning.     

用于脉冲多普勒雷达的高速数字自动增益控制(DAGC)系统

本文从ＡＧＣ的本质入手，避开复杂的数学计算，提出了一种新的地址指针查表式的ＤＡＧＣ系统，介绍了该系统的工作原理及工作流程。