A novel control scheme for the multilevel rectifier/inverter

A novel three-level pulsewidth modulation (PWM) rectifier/inverter is proposed: this single-phase three-level rectifier with power factor correction and current harmonic reduction is proposed to improve power quality. A three-phase three-level neutral point clamped (NPC) inverter is adopted to reduce the harmonic content of the inverter output voltages and currents. In the adopted rectifier, a switching mode rectifier with two AC power switches is adopted to draw a sinusoidal line current in phase with mains voltage. The switching functions of the power switches are based on a look-up table. To achieve a balanced DC-link capacitor voltage, a capacitor voltage compensator is employed. In the NPC inverter, the three-level PWM techniques based on the sine-triangle PWM and space vector modulation are used to reduce the voltage harmonics and to drive an induction motor. The advantages of the adopted th-ree-level rectifier/inverter are (1) the blocking voltage of power devices (T1, T2, S_a1-S_c4) is clamped to half of the DC-link voltage, (2) low conduction loss with low conduction resistance due to low voltage stress, (3) low electromagnetic interference, and (4) low voltage harmonics in the inverter output. Based on the proposed control strategy, the rectifier can draw a high power factor line current and achieve two balance capacitor voltages. The current harmonics generated from the adopted rectifier can meet the international requirements. Finally, the proposed control algorithm is illustrated through experimental results based on the laboratory prototype.     

基于3D打印的Ku/Ka频段双波束天线设计

提出一种采用3D打印技术设计制造的径向开孔分层龙伯透镜天线, 该天线以低损耗的石蜡强化聚苯乙烯为基材, 透镜直径为700 mm, 结构形式为7层半球龙伯透镜.天线工作在Ku/Ka频段, 可同时对准两个目标.研究表明:采用3D打印技术制造的低损耗介质径向开孔分层龙伯透镜天线实现了较高性能, 有效解决了传统加工方式加工困难、一致性差的问题, 可以容易地通过采用更小介电损耗的材料实现更优良的天线性能.     

EMI 电源滤波器在加固中选择和应用

国军标中对加固本军用终端设备电磁兼容性的要求是比较高的,要想使军用终端设备取得良好的电磁兼容性,除 了要加强机箱和电缆的屏蔽外,EMI 电源滤波器的性能对整机的电磁兼容性有着很大的影响,本文主要研究了电源滤波 器在解决电磁兼容性问题中的作用,介绍了电源滤波器的工作原理,分析在实践中对电源滤波器参数的选择,以及在工 程安装使用的正确方法,从而了解和掌握运用电源滤波器解决电磁兼容性问题的方法。     

表层掺杂板条状激光模块仿真研究分析

介绍了一种表层增益板条状激光器模块。提出一种结合光线追迹、有限元、数值分析的仿真方法,建立表层增益激光增益模块的模型。在求解抽运光在该结构内部的分布情况以及其温度场的分布情况时,发现与传统体掺杂的CCEPS结构相比,表层增益激光模块有较高的散热能力以及较低的光学畸变。     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.     

石英玻璃中杂质对光纤损耗影响的研究

石英玻璃根据生产加工的工艺可以分为四类,不同工艺生产的石英玻璃其杂质含量也不相同.石英玻璃作为光纤预制棒生产过程中必不可少的辅助材料[1],其中的杂质含量会对生产的预制棒最终的拉丝光纤衰减产生影响.为避免因杂质吸收产生的衰减,需要根据使用的工况要求选择合适的石英玻璃.     

Indirect test of M-S circuits using multiple specification band guarding

Testing analog and mixed-signal circuits is a costly task due to the required test time targets and high end technical resources. Indirect testing methods partially address these issues providing an efficient solution using easy to measure CUT information that correlates with circuit performances. In this work, a multiple specification band guarding technique is proposed as a method to achieve a test target of misclassified circuits. The acceptance/rejection test regions are encoded using octrees in the measurement space, where the band guarding factors precisely tune the test decision boundary according to the required test yield targets. The generated octree data structure serves to cluster the forthcoming circuits in the production testing phase by solely relying on indirect measurements. The combined use of octree based encoding and multiple specification band guarding makes the testing procedure fast, efficient and highly tunable. The proposed band guarding methodology has been applied to test a band-pass Butterworth filter under parametric variations. Promising simulation results are reported showing remarkable improvements when the multiple specification band guarding criterion is used.     

一种用于接收机的低功耗自动增益控制环路

This paper proposes a new structure to lower the power consumption of a variable gain amplifier (VGA) and keep the linearity of the VGA unchanged. The structure is used in a high rate amplitude-shift keying (ASK) based IF-stage. It includes an automatic gain control (AGC) loop and ASK demodulator. The AGC mainly consists of six-stage VGAs. The IF-stage is realized in 0.18 μ m CMOS technology. The measurement results show that the power consumption of the whole system is very low. The system consumes 730 μ A while operating at 1.8 V. The minimum ASK signal the system could detect is 0.7 mV (peak to peak amplitude).     

Enhanced fair earliest due date first scheduling strategy for multimedia applications in LTE downlink framework

Guaranteeing a certain delay threshold for delay‐sensitive applications in long term evolution (LTE) cellular communication system is a very challenging mission. By implementing an optimal scheduling strategy, this mission will be achieved. In this article, a novel scheduler is introduced in order to meet a predefined level of service quality by guaranteeing a specific delay threshold for delay‐sensitive applications in LTE cellular systems. The proposed scheduler assigns the available resource blocks (RBs) to active user equipments (UEs) tacking into consideration several attributes. The expiration date of each packet, the channel quality, the average data rate previously achieved by each UE, and the number of dropped packets for each UE compared with the average number of packets totally dropped are all considered in the proposed scheduler working mechanism. Consequently, the proposed scheduling strategy reduces the number of packets dropped for multimedia applications, and at the same time maximizes the overall throughput of the network. Simulation results are provided to study and evaluate the performance of the proposed scheduling strategy. A comparative study is presented between the proposed strategy and the most recent scheduling techniques. The obtained results prove that the proposed scheduling strategy has considerably acceptable and appreciated results compared with the results of the state‐of‐the‐art scheduling techniques.     

基于光纤环形镜的Er3＋/Yb3＋共掺双包层光纤放大器的增益平坦化

基于光纤环形镜(FLM)的结构及其滤波特性的理论 分析,采用FLM实现铒镱(Er3＋/Yb3＋)共掺双包 层光纤放大器(EYDFA)的增益平坦化。进行MATLAB仿真,并实验研究了含有1段保偏光纤(P MF) 和含有2段PMF的FLM的滤波特性,分析了其滤波特性随PMF长度及偏振控 制器(PC)状态的变化情况、FLM的PMF段数与长度的选取问题;使用含有2段PMF的 FLM进行了增益平坦实验,实现了自发辐射(ASE)谱两峰的平坦,在其所处的主 要波 长范围1535~1547nm内, 增益不平坦度由±7.5dB减小到±0.75dB。将宽谱光源的输出光信号作为信 号光输入放大系统,在波长1535~1547nm范围内,放大器的增益不平 坦度由±4.5dB降为±1.2dB。