4.9-GHz low-phase-noise transformer-based superharmonic-coupled GaInP/GaAs HBT QVCO

The low-phase-noise GaInP/GaAs heterojunction bipolar transistor (HBT) quadrature voltage controlled oscillator (QVCO) using transformer-based superharmonic coupling topology is demonstrated for the first time. The fully integrated QVCO at 4.87GHz has phase noise of -131dBc/Hz at 1-MHz offset frequency, output power of -4dBm and the figure of merit (FOM) -198dBc/Hz. The state-of-the-art phase noise FOM is attributed to the superior GaInP/GaAs HBT low-frequency device noise and the high quality transformer formed on the GaAs semi-insulating substrate.     

Discrete-time analysis of a CPCH access scheme in W-CDMA

Common packet channel (CPCH) access is an efficient approach to support packet data transmissions in a wideband code division multiple access (W-CDMA) system. Rather than using a continuous-time analysis approach, this paper presents a discrete-time analysis of the CPCH access scheme to fully characterize the complete CPCH operation process. Previous studies using the continuous-time analysis only models a portion of the CPCH process. We assume that a packet arrival process is Poisson distributed and the service time of each packet is geometrically distributed. The study focuses on examining the number of packet arrivals in each CPCH access slot. Performance is evaluated in terms of normalized throughput and it is observed that CPCH performs better when packet mean service time is larger. The performance results are also compared with previous studies using continuous-time analyses     

InGaP/InGaAs Pseudomorphic Heterodoped-Channel FETs With a Field Plate and a Reduced Gate Length by Splitting Gate Metal

Depositing gate metal across a step undercut between the Schottky barrier layer and the insulator-like layer is employed to obtain a reduced gate length of 0.4 mum with an additional 0.6-mum field plate from a 1-mum gate window. Most dc and ac characteristics including current density (I_DSS=451mA/mm), transconductance (g_m,max=225mS/mm), breakdown voltages (V_BD(DS)/V _BD(GD)=22/-25.5V), gate-voltage swing (GVS=2.24V), cutoff, and maximum oscillation frequencies (f_t/f_max=17.2/32GHz) are improved as compared to those of a 1-mum gate device without field plate. At a V_DS of 4.0 V, a maximum power added efficiency of 36% with an output power of 13.9 dBm and a power gain of 8.7 dB are obtained at a frequency of 1.8 GHz. The saturated output power and the linear power gain are 316 mW/mm and 13 dB, respectively     

高温黑体空腔发射率有限元分析

基于有限元热分析方法,建立了不同形状的黑体空腔传感器模型,并对其腔体发射率进行求解,同时讨论了腔体开口、腔长、腔口与接收面之间的距离、材料自身的发射率等参数对腔体发射率的影响,通过对各种形状黑体空腔的发射率比较,得出最佳的黑体空腔设计方案.仿真结果表明,改变影响腔体几何结构的各参数时,黑体空腔腔体发射率也随之变化,当黑...     

多波长加权回归准确计算F-P标准具的间隔

漫射单色光经F-P标准具产生一组干涉圆环,对环直径平方与干涉级次的经典一阶方程加上二阶修正项,从修正后的准直线方程能够确定圆环中心干涉级次的小数部分.实验采用波长相近的两条汞黄线、氦黄线和氖黄线作为光源,同时获得经F-P标准具的四组千涉圆环.对圆环的点位坐标数据作圆回归求得直径值及其标准差,进而用新的准直线模型作加权回...     

从“伪养生”现象看科学传播与医学科普

2010年"伪养生"等现象震惊了医学界,本文从科学传播的角度,分析医学科普的现状、存在问题,提出医学科普应由医学专业人士来做,通过科学的方法和技巧使公众易于接受,政府支持是医学知识传播的组织保障,大众媒体是医学知识科学传播的重要途径。     

无线电监测系统的组成与应用

描述了我国无线电监测系统的发展现状和背景,分析了无线电监测系统的原理和结构,说明了其在自动监测模式和手动监测模式下的运行机制。最后针对场强覆盖预测系统,从电波传播模型的选取、系统主要功能、以及GIS技术在场强覆盖预测系统中的应用等方面进行了说明。通过采用GIS中的空间分析和三维分析技术,就能对场强预测系统进行二次开发,提升其性能。     

某鱼雷空中姿态控制装置自动测试系统的设计

通过对某鱼雷空中姿态控制装置进行分析与研究,并对被测对象测试需求特征进行综合分析,优化测试项目,优化测试资源配置,设计出适用的空中姿态控制装置测试设备。测试仪硬件采用基于ISA总线结构的工控机,软件采用LabWindows/CVI开发平台。     

基于Modbus的远程监控

通过对Modbus的研究,利用LabView平台实现了客户端程序,完成了对网络上支持该协议的设备的访问。以研华公司提供的ADAM-6050为例,实现了对其的实时远程监控,以及灵活配置。     

In Situ X‐Ray Diffraction Studies on Structural Changes of a P2 Layered Material during Electrochemical Desodiation/Sodiation

Sodium layered oxides with mixed transition metals have received significant attention as positive electrode candidates for sodium‐ion batteries because of their high reversible capacity. The phase transformations of layered compounds during electrochemical reactions are a pivotal feature for understanding the relationship between layered structures and electrochemical properties. A combination of in situ diffraction and ex situ X‐ray absorption spectroscopy reveals the phase transition mechanism for the ternary transition metal system (Fe–Mn–Co) with P2 stacking. In situ synchrotron X‐ray diffraction using a capillary‐based microbattery cell shows a structural change from P2 to O2 in P2–Na_0.7Fe_0.4Mn_0.4Co_0.2O₂ at the voltage plateau above 4.1 V on desodiation. The P2 structure is restored upon subsequent sodiation. The lattice parameter c in the O2 structure decreases significantly, resulting in a volumetric contraction of the lattice toward a fully charged state. Observations on the redox behavior of each transition metal in P2–Na_0.7Fe_0.4Mn_0.4Co_0.2O₂ using X‐ray absorption spectroscopy indicate that all transition metals are involved in the reduction/oxidation process.