MPEG-4: a multimedia standard for the third millennium. 2

MPEG-4 defines a multimedia system for interoperable communication of complex scenes containing audio, video, synthetic audio, and graphics material. In part 1 of this two-part article (Battista et al., 1999) we provided a comprehensive overview of the technical elements. In part 2 we describe an application scenario based on digital satellite television broadcasting, discuss the standard's envisaged evolution, and compare it to other activities in forums addressing multimedia specifications     

Cryogenic 2?4 GHz f.e.t. amplifier

A cryogenic single-stage broadband f.e.t. amplifier with an average noise temperature of 34 K (0.5 dB) over a bandwidth of 2 GHz has been developed. The average gain is 12 dB. The best spot noise temperature is 17 K (0.25 dB) at 3.2 GHz, which is competitive with cryogenic parametric amplifiers.     

一种2.4GHz正交输出频率综合器

介绍了一种用于bluetooth的基于0.35μm CMOS工艺的2.4GHz正交输出频率综合器的设计和实现.采用差分控制正交耦合压控振荡器实现I/Q信号的产生.为了降低应用成本,利用一个二阶环路滤波器以及一个单位增益跨导放大器来代替三阶环路滤波器.频率综合器的相位噪声为-106.15dBc/Hz@1MHz,带内相位噪声小于-70dBc/Hz,3.3V电源下频率综合器的功耗为13.5mA,芯片面积为1.3mm×0.8mm.     

SrAl2O4 ：Eu2+和SrAl2O4 ：Eu2+，Dy3+长余辉和热释光谱

对比研究了SrAl2O4:Eu2+和SrAl2O4:Eu2+,Dy3+的余辉特性和热释光谱,并探讨了Dy3+的掺杂对SrAl2O4:Eu2+陷阱能级的影响。XRD晶相分析表明: Eu2+和Dy3+的掺杂并没有改变SrAl2O4的晶体结构。发光分析表明：Dy3+的掺杂没有改变SrAl2O4:Eu2+的光致发光光谱和发光中心。热释光谱对比分析结果显示：Eu2+的掺杂在SrAl2O4的禁带中引入了两个深度不同的陷阱能级;Dy3+的掺杂并不改变原来陷阱能级的深度,却能够显著地增加原来浅陷阱能级的密度,从而改善了SrAl2O4:Eu2+的余辉特性。不同等待时间的热释光谱曲线显示：在室温下,不同陷阱能级衰减规律的差异以及陷阱能级间存在的电子转移,可能造成了SrAl2O4:Eu2+,Dy3+长余辉材料复杂的余辉衰减规律。     

Enhanced efficiency of organic photovoltaic cells with Sr2SiO4:Eu2+ and SrGa2S4:Eu2+ phosphors

We report the effect of yellow Sr₂SiO₄:Eu²⁺ and green SrGa₂S₄:Eu²⁺ phosphors on the efficiency of organic photovoltaic (OPV) cells. Each phosphor was coated on the back side of indium tin oxide (ITO)/glass substrates by spin coating with poly(methyl methacrylate) (PMMA). The maximum absorption wavelength of the active layer in the OPV cells was ～512 nm. The emission peaks of Sr₂SiO₄:Eu²⁺ and SrGa₂S₄:Eu²⁺ were maximized at 552 nm and 534 nm, respectively. The short circuit current density (J_sc) and power conversion efficiency (PCE) of the OPV cells with Sr₂SiO₄:Eu²⁺ (8.55 mA/cm² and 3.25%) and with SrGa₂S₄:Eu²⁺ (9.29 mA/cm² and 3.3%) were higher than those of the control device without phosphor (7.605 mA/cm² and 3.04%). We concluded that phosphor tuned the wavelength of the incident light to the absorption wavelength of the active layer, thus increasing the J_sc and PCE of the OPV cells.     

一种2.4GHz正交输出频率综合器

介绍了一种用于bluetooth的基于0.35μm CMOS工艺的2.4GHz正交输出频率综合器的设计和实现.采用差分控制正交耦合压控振荡器实现I/Q信号的产生.为了降低应用成本,利用一个二阶环路滤波器以及一个单位增益跨导放大器来代替三阶环路滤波器.频率综合器的相位噪声为-106.15dBc/Hz@1MHz,带内相位噪声小于-70dBc/Hz,3.3V电源下频率综合器的功耗为13.5mA,芯片面积为1.3mm×0.8mm.     

基于COMSOL4.2的波导模式特性仿真

本文介绍了使用电磁场仿真工具COMSOL 4.2进行仿真的一般步骤,以及使用COMSOL 4.2对基本类型光波导模式特性进行仿真的实例,并介绍了在此基础上进行光波导模式特性仿真实验设计中的几个教学重点,遵循由简单到复杂、由理论到实践、由演示到设计的思维训练过程。基于COMSOL 4.2的光波导模式特性仿真实验主要应用于"光纤通信"课程的实践化教学中,COMSOL 4.2的使用也可引入到其他场类课程的教学中。     

ZnCr_2O_4陶瓷湿度检测新方法

电阻型湿敏陶瓷在湿度检测上的应用有一定局限性，采用ＺｎＣｒ２Ｏ４系陶瓷检测湿度可以避免这种局限性。通过实验研究了ＣＯ、ＣＯ２、ＳＯ２、Ｈ２Ｓ、ＮＨ３、ＣＨ３ＯＨ及Ｃ２Ｈ５ＯＨ七种气体对湿度检测的干扰情况。结果证明，这种方法是可行的。     

MPEG-4第2部分与H.264比较

MPEG-4第2部分和H.264是最新的视频编码标准，分析和比较这两种视频编码标准，在此基础上对设计视频编码标准提出一些看法。     

Bioinspired Design of SrAl2O4:Eu2+ Phosphor

A phosphor based on Sr_0.97Al₂O₄:Eu_0.03 with a biomorphous morphology is manufactured via vacuum assisted infiltration of wood tissue (Pinus sylvestris) with a precursor nitrate solution. The nitrate solution penetrates homogeneously into the uniform arrangement of rectangular shaped tracheidal cells of the wood tissue. According to scanning electron microscopy, the original wood cell walls are completely transformed retaining the original wood structure. The major crystalline phase is monoclinic SrAl₂O₄, detected by X‐ray diffraction and confirmed by Rietveld refinement. Energy‐dispersive X‐ray analysis proves the homogeneous conversion of the original wood cell wall into Sr_0.97Al₂O₄:Eu_0.03 struts. The optical properties of the resulting phosphor material are determined by photoluminescence and cathode‐luminescence spectroscopy in scanning electron microscopy. The biotemplated Sr_0.97Al₂O₄:Eu_0.03 shows a characteristic green emission at 530 nm (2.34 eV). Shaping biomorphous SrAl₂O₄:Eu²⁺ phosphor with a microstructure pseudomorphous to the bioorganic template anatomy offers a novel approach for designing micropatterned phosphor materials.     

Multi-Mode Optical Manometry Based on Li4SrCa(SiO4)2:Eu2+ Phosphors

Optical manometry is a highly promising method for measuring pressure. However, its wider application is limited by the lower sensitivity and influenced by environmental factors. Herein, multi-mode optical pressure sensors based on Eu²⁺-doped Li₄SrCa(SiO₄)₂ phosphors suitable for a variety of complex pressure-measuring environments are designed. The phosphors contain two separate luminescence centers at 443 nm (Eu_Sr) and 584 nm (Eu_Ca), respectively. In the lower pressure range, the emission peak undergoes a massive redshift of 5.19 nm GPa⁻¹ of Eu_Ca, which is 14× better than commercially available ruby sensors. In order to improve the pressure response range and the accuracy of pressure measurement, for the first time, a new approach in the pressure readout method in which single Eu²⁺ ions doping based on fluorescence intensity ratio (FIR) pressure measurement is realized in designed materials. Meanwhile, the measured full width at half maximum (FWHM) as an indicator of pressure sensor performance also reveals that the sensing performance is d FWHM/d P ≈ 1.23 nm GPa⁻¹ and d FWHM/d P ≈ 0.84 nm GPa⁻¹ for Eu_Sr and Eu_Ca positions, respectively. Additionally, the structural stability of the phosphor is confirmed by in situ Raman spectrum. The above results indicate that the Li₄SrCa(SiO₄)₂:0.04Eu²⁺ phosphor is a good candidate for multi-mode optical pressure sensors.     

一种适用于IEEE802．15．4（ZigBee）标准的2．4GHz CMOS射频收发机设计

本文提出了一种适用于IEEE 802．15．4标准的2.4GHz免认证ISM频段的全集成CMOS射频收发机．接收机采用低中频结构以降低功耗、提高灵敏度,发射机则采用直接上变频结构以降低设计复杂度和功耗．芯片采用0.18μm 1P4M CMOS工艺以及MIM电容制造,供电电压1.8V ．测试结果显示,在误包率为1％时,接收机灵敏度达到了-97dBm ,发射机输出至100Ω差分天线端口的最大输出功率为＋3dBm ．接收模式和发射模式下的电流功耗分别为17mA和19mA ,芯片面积3.3mm ×2.8mm ．