Virtual impedance control for a regional dynamic voltage restorer

A dynamic voltage restorer (DVR) can be installed in a middle-voltage (MV) power grid, to concurrently protect a cluster of sensitive loads from voltage sags. To further improve its efficiency and reduce the difficulty in its implementation, a novel control strategy for operating such a DVR as a virtual impedance in series with sensitive loads is proposed in this paper. In addition to its usual function of compensating for voltage sags, such a DVR can also operate as a virtual inductance, to function as a fault current limiter (FCL) during a downstream fault, or a virtual capacitance, to function as a series compensator (SC) to compensate the voltage loss along the feeder line during heavy load. Based on a dual-loop control design, strategies for operating a DVR as a series virtual inductance and a virtual capacitance are proposed, and methods for tuning the parameter values and a stability analysis of the whole system are presented. The feasibility and effectiveness of the proposed method are verified by simulations using the PSCAD software, and experimental results obtained using a prototype DVR are presented.     

Some Theoretic Results on a Digital EMG Signal Processor

As is well known, a general EMG signal processing scheme includes a prewhitening filter, a v-order detector, a smoothing filter, and a relinearizer. In this paper, a theoretical analysis of such a scheme is carried out, including a detector characteristic which presents a logarithmic behavior.     

A 1.8-V operation RF CMOS transceiver for 2.4-GHz-band GFSK applications

This paper describes a single-chip RF transceiver LSI for 2.4-GHz-band Gaussian frequency shift-keying applications, such as Bluetooth. This chip uses a 0.18-/spl mu/m bulk CMOS process for lower current consumption. The LSI consists of almost all the required RF and IF building blocks: a transmit/receive antenna switch, a power amplifier, a low noise amplifier, an image rejection mixer, channel-selection filters, a limiter, a received signal strength indicator, a frequency discriminator, a voltage controlled oscillator, and a phase-locked loop synthesizer. The bandpass filter for channel selection was difficult to achieve since it operates at a low supply voltage. However, because large interference is roughly rejected at the output of the image rejection mixer and a wide-input-range bandpass filter with an optimized input bias is realized, the transceiver can operate at a supply voltage of 1.8 V. In the IF section, we adopted a circuit design using the minimum number of passive elements, resistors and capacitors, for a lower chip area of 10.2 mm/sup 2/.     

Modeling the flow-level performance of hierarchical modulation in?OFDMA-based networks

Hierarchical Modulation (HM) is a means to enhance the spectral efficiency of a system by superposing, in terms of modulation, an additional stream for a given user with good radio conditions on a basic stream of a user with worse radio conditions. This, in turn, increases the throughput of the former user and hence the overall performance of the whole system. We consider, in this work, such a performance at the flow level, for a realistic dynamic setting where users come to the system and leave it after a finite duration corresponding, for instance, to the completion of a file transfer. We specifically model and quantify, both analytically and via simulations, the gain thus achieved and propose two extensions to the basic HM algorithm: a first one in which a user with bad radio conditions is also superposed on one with better radio conditions and a second one in which a user of one type is further superposed on a user of the same type as well.     

A bi-directional transceiver PIC for ping-pong local loop configurations operating at 1.3-/spl mu/m wavelength

We propose and demonstrate a simple, potentially low-cost, photonic integrated circuit that can operate as a transceiver in a ping-pong optical data-link configuration. The device is designed for uncooled operation, with a gain section, a detector, and a beam expander inside a Fabry-Perot cavity. The detector has a 1.4 /spl mu/m quaternary layer with a broad spectral responsivity range extending to 33 nm higher than the lasing wavelength of the device. The transmitter can provide 8 dBm inside a single-mode fiber, and the beam expander relaxes the alignment tolerance to a single-mode fiber.     

MEMS红外探测器响应时间测量方法研究

传统地,MEMS红外探测器响应时间的测量需要基于黑体辐射源、斩波器、水冷装置等设备搭建一套复杂的测量系统,然而斩波器的遮挡区域和透光区域具有一定的面积,其按某频率工作时会消耗一定的时间,而测试所得的器件响应时间无法排除斩波器的工作耗时,导致测试结果存在较大误差,所测响应时间为14.46ms。为解决这一问题,提出了一种以钛宝石激光器为辐射光源,利用声光调制器构建纳秒级激光脉冲,MEMS红外探测器响应激光脉冲的作用输出脉冲电信号,很好地规避了测量系统中设备工作耗时引入的时间参数,所测响应时间仅为3.13ms。由此可见,传统方法中斩波器工作耗时引入的时间误差甚至超过器件响应时间的300%,充分证明了此方法可以有效解决这一问题,进而为MEMS红外探测器以及其它光学探测器性能参数的测试与计量提供了一种新的方法。     

环Zn上椭圆曲线的密钥交换协议

设n=pq,p,q为奇素数,环Z_n上的椭圆曲线E_n(a,b)的SOM密钥交换协议与QV密钥交换协议均选取E_n(a,b)上的阶为M_n=lcm{#E_p(a,b),＃E_q(a,b)}的点G作为公钥(称G为基点),并且限定其对应的E_p(a,b)和E_q(a,b)均为循环群,这就限制了这两个协议只能选择一类特殊的椭圆曲线E_n(a,b)构作密钥交换协议.本文指出,E_p(a,b)和Eq(a,b)均为循环群这一限定是不必要的.本文给出了E_n(a,b)上存在阶为M_n的点G的一个充分必要条件,并给出一个例子,其中E_p(a,b)为循环群,E_q(a,b)为非循环群,且对应的E_n(a,b)上有阶为M_n的点G.同时,本文选取E_n(a,b)上阶为lcm{n₁,m₁}的点作为基点,这里n₁,m₁分别为E_p(a,b)和E_q(a,b)的最大循环子群的阶.这样,就能够选择更多的椭圆曲线E_n(a,b),用来构作密钥交换协议(包括将两方之间的密钥交换协议扩展到三方).     

Firewalls fend off invasions from the Net

Whether a computer is in a corporation, government agency, university, small business, or at home, if it is linked to a network, hackers are a risk. The first line of defense against them is a firewall, provided it is set up correctly. Firewall technology is a set of mechanisms that collectively enforce a security policy on communication traffic entering or leaving a guarded network domain. The security policy is the overall plan for protecting the domain. Embodied in hardware, software, or both, a firewall guards and isolates the domain. Broadly, firewalls attempt to maintain privacy and ensure the authenticity of data communications that pass through their domain's boundaries. Whether data is entering or leaving a domain, it is protected from eavesdropping (passive wiretapping) and change (active wiretapping). But only communication traffic entering or leaving a domain comes under the influence of firewall technology     

A double-gate-type static-induction thyristor

A double-gate-type static-induction thyristor (DG-SIThy) with a high blocking voltage and a high current rating has been fabricated. In this paper, a basic operational mechanism, a fabrication procedure, and the electrical characteristics of the DG-SIThy are described. In the DG-SIThy, both electron injection and hole injection are controlled by signals applied to two gale regions so that the DG-SIThy is capable of higher frequency operations than a single-gate SIThy. In the DG-SIThy, described here, both a cathode and a gate (first gate) regions have been fabricated on one side of a semiconductor wafer and both an anode and gate.(second gate) regions on another side. For realizing the DG-SIThy with a high blocking voltage and a high current rating, we have tried attentively to form a p-n junction on one side of the wafer without influencing the p-n junction on the other side, and have developed a new counter-doping technique for epitaxial growth and an improved package structure for a compression-mounted device. The DG-SIThy fabricated with these techniques has shown a for-Ward blocking voltage of 1000 V, an average current rating of 100 A, and a forward voltage drop of 1.44 V at the rated anode current. A turn-on time of 0.95 its and a turn-off time of 0.48 µs have been observed at the rated anode current and at anode voltages of 650 and 550 V, respectively. As already speculated, the DG-SIThy shows a higher switching speed and a lower forward drop than the single-gate SIThy.     

A Binary-Weighted Switching and Reconfiguration-Based Programmable Gain Amplifier

In previous works, the authors reported on binary-weighted switching and reconfiguration techniques to design programmable gain amplifiers (PGAs) with a wide decibel (dB)-linear range, a small gain error, a wide 3-dB bandwidth, and high linearity. In this brief, two techniques are analyzed in more detail. Adopting the two techniques, a new low-voltage PGA version is proposed that offers a precise and process/temperature-insensitive gain and achieves a double dB-linear range with a small gain error while maintaining the same chip size, as compared with those of previous designs. Implemented in 0.18-mum CMOS, from the measurements, the proposed PGA shows a dB-linear gain range of 42 dB (-21 to 21 dB) with a gain error of less than plusmn 0.54 dB, a maximum input-referred third-order intercept point (IIP3) of 14 dBm, and a 3-dB bandwidth of 60 MHz at the maximum gain while consuming only 2.1 mA from a 1.5-V supply.     

液晶红外传感器系统

液晶红外传感器系统包括液晶斩波器,驱动电路、液晶聚合物热电元件、探测器、放大器和显示器等。液晶斩波器还可应用于温差电堆、热敏电阻测辐射热仪、红外摄象机等。热电液晶聚合物还可用作压电、驻极体、非线性光学元件等。     

Ultra-Low-Power Interface Chip for Autonomous Capacitive Sensor Systems

Traditionally, most of the sensor interfaces must be tailored towards a specific application. This approach results in a high recurrent design cost and time to market. On the other hand, generic sensor interface design reduces the costs and offers a handy solution for multisensor applications. This paper presents a generic sensor interface chip (GSIC), which can read out a broad range of capacitive sensors. It contains capacitance-to-voltage converters, a switched-capacitor amplifier, an analog-to-digital converter, oscillators, clock generation circuits and a reference circuit. The system combines a very low-power design with a smart energy management, which adapts the current consumption according to the accuracy and speed requirements of the application. The GSIC is used in a pressure and an acceleration monitoring system. The pressure monitoring system achieves a current drain of 2.3 muA for a 10-Hz sample frequency and an 8-bit accuracy. In the acceleration monitoring system, we measured a current of 3.3 muA for a sample frequency of 10 Hz and an accuracy of 9 bits     

Impact of Channel Errors on Decentralized Detection Performance of Wireless Sensor Networks: A Study of Binary Modulations, Rayleigh-Fading and Nonfading Channels, and Fusion-Combiners

We provide new results on the performance of wireless sensor networks in which a number of identical sensor nodes transmit their binary decisions, regarding a binary hypothesis, to a fusion center (FC) by means of a modulation scheme. Each link between a sensor and the fusion center is modeled independent and identically distibuted (i.i.d.) either as slow Rayleigh-fading or as nonfading. The FC employs a counting rule (CR) or another combining scheme to make a final decision. Main results obtained are the following: 1) in slow fading, a) the correctness of using an average bit error rate of a link, averaged with respect to the fading distribution, for assessing the performance of a CR and b) with proper choice of threshold, on/off keying (OOK), in addition to energy saving, exhibits asymptotic (large number of sensors) performance comparable to that of FSK; and 2) for a large number of sensors, a) for slow fading and a counting rule, given a minimum sensor-to-fusion link SNR, we determine a minimum sensor decision quality, in order to achieve zero asymptotic errors and b) for Rayleigh-fading and nonfading channels and PSK (FSK) modulation, using a large deviation theory, we derive asymptotic error exponents of counting rule, maximal ratio (square law), and equal gain combiners.     

A Note on Loaded Line Synthesis (Correspondence)

The purpose of this note is to present an alternate derivation of a formula for the synthesis of a loaded line. The problem is to determine the values of the normalized susceptances a and c mounted an exact quarter-wavelength apart along a uniform line. These are arranged in the order a, c, c,. . .c, a to achieve a loaded line with a given phase shift and perfect match. In order to analyze a particular line design for standing-wave ratio and phase shift over a band of frequencies on a digital computer, it is worthwhile to know the values of the susceptances to many more decimal places than one would achieve from a simple graph.     

High-speed driving method using bipolar scan waveform in AC plasma display panel

This paper proposes a new high-speed driving method using the bipolar scan waveform with a scan width of 1 /spl mu/s in an ac-plasma display panel. The bipolar scan waveform in an address period consists of a two-step pulse with two different polarities, i.e., a forward scan pulse with a negative polarity and reverse scan pulse with a positive polarity, which can produce two address discharges, including a primary address discharge for generating wall charges and secondary address discharge for accumulating wall charges. To produce the fast address discharge stably using the bipolar scan pulse during an address period, a new reset waveform is designed based on a V/sub t/ close curve analysis, and the address discharge characteristics examined under various reset and address waveforms. As a result of adopting the proposed driving method, a high-speed address with a scan width of 1 /spl mu/s is successfully obtained when using a checkered pattern on a 4-in test panel.     

Measuring the Object Deformation by Real Time Holographic Interferometry with Automatically Calculating Hologram

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Multilayer context cloud framework for mobile Web 2.0: a proposed infrastructure

Existing context‐aware systems focus only on characterizing the situation of an entity to exhibit the advantage of contextual information association, but they have no mechanism to facilitate the interoperation and reuse of contextual information. Cloud computing offers an adaptable and flexible solution for existing context‐aware applications, integrating Mobile Web 2.0 technologies. This work presents a multilayer context cloud framework (MCCF) that integrates Web 2.0 technologies into a mobile context‐aware system for use in a cloud computing environment. The proposed MCCF includes a context sensor layer, a context information layer, a context service layer, a context representation layer, a cloud computing layer, and a mobile Web 2.0 context‐aware Software as a Service layer. To demonstrate the feasibility of this approach, a Mobile Web 2.0‐based context‐aware Software as a Service platform, which is a cloud computing application based on MCCF, is implemented to provide continuous and context‐aware monitoring of a specific application. Copyright © 2011 John Wiley & Sons, Ltd.     

Digital image watermarking employing codebook in vector quantisation

Two simple watermarking techniques for a digital image are proposed. The methods employ a codebook in vector quantisation, and can extract watermark information from a watermarked image without an original image. Simulation results show that when the codebook of a larger size is used, a reconstructed image with a watermark has better quality than that without a watermark, and, for one of the proposed methods, a watermark size and the percentage of 0 bit contained in a watermark have almost no effect on PSNR for a reconstructed image.     

Polarization control in a vertical cavity surface emitting laser submitted to optical feedback

We study experimentally and theoretically two polarization effects in a vertical cavity surface emitting laser submitted to optical feedback. In a first experiment, we obtain flips between two linearly polarized laser modes up to a frequency of 50 MHz using an external cavity with a polarizer. In a second experiment, polarization self modulation is demonstrated up to a frequency of 2.6 GHz, using a quarter wave plate instead. Numerical calculations, based on a four levels model for the active medium, show a good agreement with the experiments.