A Single-Phase Active Filter Using an H-Bridge PWM Converter With a Sampling Frequency Quadruple of the Switching Frequency

This paper presents a digital current regulator for H-bridge pulsewidth modulation (PWM) converters, whose sampling frequency equals quadruple of the switching frequency. The current regulator detects the ac current and manipulates the voltage reference not only at the upper and lower peaks of the PWM triangle carrier but also at its zero crossings. This paper theoretically discusses the switching sequence of the H-bridge PWM converter, and reveals the amount of the voltage error and the condition where the voltage error occurs. A modified deadbeat current regulator is proposed to suppress the current oscillation induced by the voltage error, based on the theoretical analysis. Experimental results are shown to verify the control performance of the proposed current regulator. Moreover, a proposed current regulator is applied to a single-phase active power filter to demonstrate the effectiveness in harmonic compensation.     

Error-resilient video communications over CDMA networks with a bandwidth constraint.

We present an adaptive video transmission scheme for use in a code-division multiple-access network, which incorporates efficient bandwidth allocation among source coding, channel coding, and spreading under a fixed total bandwidth constraint. We derive the statistics of the received signal, as well as a theoretical bound on the packet drop rate at the receiver. Based on these results, a bandwidth allocation algorithm is proposed at the packet level, which incorporates the effects of both the changing channel conditions and the dynamics of the source content. Detailed simulations are done to evaluate the performance of the system, and the sensitivity of the system to estimation error is presented.     

Transport-Coefficient Dependence of Current-Induced Cooling Effect in a Two-Dimensional Electron Gas

The dependence of the current-induced cooling effect on the electron mobility??? _e is explored for a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We calculate the distributions of the electrochemical potentials and the temperatures under a magnetic field, fully taking account of thermoelectric and thermomagnetic phenomena. Whereas the electrochemical potential and the electric current remain qualitatively unchanged, the temperature distribution exhibits drastic mobility dependence. The lower-mobility system has cold and hot areas at opposite corners, which results from the heat current brought about by the Ettingshausen effect in the vicinity of the adiabatic boundaries. The cooling effect is intensified by an increase in??? _e. Intriguingly, the cold and hot areas change places with each other as the mobility??? _e is further increased. This is because the heating current on the adiabatic edges due to the Righi?CLeduc effect exceeds that due to the Ettingshausen effect in the opposite direction.     

A Retargetable Compilation Methodology for Embedded Digital Signal Processors Using a Machine-Dependent Code Optimization Library

We address the problem of code generation for embedded DSP systems. Such systems devote a limited quantity of silicon to program memory, so the embedded software must be sufficiently dense. Additionally, this software must be written so as to meet various high-performance constraints. Unfortunately, current compiler technology is unable to generate dense, high-performance code for DSPs, due to the fact that it does not provide adequate support for the specialized architectural features of DSPs via machine-dependent code optimizations. Thus, designers often program the embedded software in assembly, a very time-consuming task. In order to increase productivity, compilers must be developed that are capable of generating high-quality code for DSPs. The compilation process must also be made retargetable, so that a variety of DSPs may be efficiently evaluated for potential use in an embedded system. We present a retargetable compilation methodology that enables high-quality code to be generated for a wide range of DSPs. Previous work in retargetable DSP compilation has focused on complete automation, and this desire for automation has limited the number of machine-dependent optimizations that can be supported. In our efforts, we have given code quality higher priority over complete automation. We demonstrate how by using a library of machine-dependent optimization routines accessible via a programming interface, it is possible to support a wide range of machine-dependent optimizations, albeit at some cost to automation. Experimental results demonstrate the effectiveness of our methodology, which has been used to build good-quality compilers for three fixed-point DSPs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inhibiting Surface Diffusion to Synthesize 3D Bicontinuous Nanoporous N-Doped Carbon for Boosting Oxygen Reduction Reaction in Flexible All-Solid-State Al-Air Batteries

Catalyzing oxygen reduction reaction (ORR) and accelerating oxygen diffusion are two key challenges for the requirements of the cathode catalysts in the metal-air batteries. A promising strategy for improving both ORR performance and mass diffusion simultaneously is to build carbon-based catalysts with ORR-active chemical dopants and 3D interconnected porosity. Herein, a 3D nanoporous N-doped carbon with bicontinuous porosity and interconnected open-pore channels is reported, which is prepared by a polyaniline-assisted template method. The polyaniline can efficiently inhibit the surface diffusion-caused template coarsening, achieving a small pore size of 35 nm. The small porous morphology gives rise to a high N-dopant concentration up to 7.20 at.%, which in turn exhibits a commercial Pt/C-comparable ORR performance together with satisfied durability in alkaline media. Using these nanoporous carbon catalysts as air electrodes, an all-solid-state flexible Al-air battery is assembled with the measured maximum power density reaching 130.5 mW cm⁻², as compared to 106.2 mW cm⁻² when the commercial Pt/C standard is used. This study provides an efficient method to synthesize 3D N-doped carbon with bicontinuous nano-sized pore channels for wide-ranging applications in portable and flexible devices.     

Weight distribution of a class of binary block codes formed from RCPC codes

In this paper, we study the weight enumerator and the numerical performance of a class of binary linear block codes formed from a family of rate-compatible punctured convolutional (RCPC) codes. Also, we present useful numerical results for a well-known family of RCPC codes.     

Improved efficiency of polymer light-emitting diodes by inserting a hole transport layer formed without thermal treatment above glass transition temperature

We have demonstrated a significant improvement in the performance of polymer light-emitting diodes (PLEDs) by inserting the fluorene-triatylamine copolymer as hole transport layer (HTL) without a thermal treatment above the glass transition temperature (T_g). A thin HTL insolubilized by a thermal treatment above T_g is often inserted as an interlayer between an anode buffer layer and a light-emitting polymer (LEP) in PLEDs fabricated by using a conventional solution process. The evaporative spray deposition using ultradiluted solution (ESDUS) method has enabled fabricating polymer bilayer structure without an insolublizing procedure. The bilayer PLEDs fabricated by ESDUS without the thermal treatment showed significantly higher and more stable external quantum efficiency than PLEDs having the conventional interlayer. Thermal treatment above T_g of the copolymer would induce degradation of its hole injection property. Furthermore, ESDUS bilayer devices showed much higher power efficiency than interlayer devices when calcium was used for cathode. The improvements would be caused by the enhancement of hole injection and the effective electron blocking at the copolymer/LEP interface in the ESDUS bilayer devices.     

Electron microscope studies of InxGav1−xAs/GaAs/Si grown by metalorganic chemical vapor deposition

The microstructure of In_xGa_1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100) at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy. The variations in resultant island morphology and strain as a function of the In content were examined through the comparison of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island relaxation process changes for high In content.     

民用建筑电气设计抑制谐波的危害、降损节能

民用建筑随着非线性电气设备——计算机实时监控设备广泛应用,变频水泵、调频空调系统推广,电力系统中谐波危害越来越严重,电网的污染带来致命的危害已到急逼之势,净化电源、优化电气设计的可靠性和安全性。     

A 63-mW H.264/MPEG-4 audio/visual codec LSI with module-wise dynamic Voltage/frequency scaling

A single-chip H.264 and MPEG-4 audio-visual LSI for mobile applications including terrestrial digital broadcasting system (ISDB-T / DVB-H) with a module-wise, dynamic voltage/frequency scaling architecture is presented for the first time. This LSI can keep operating even during the voltage/frequency transition, so there is no performance overhead. It is realized through a dynamic deskewing system and an on-chip voltage regulator with slew rate control. By the combination with traditional low power techniques such as embedded DRAM and clock gating, it consumes only 63 mW in decoding QVGA H.264 video at 15 frames/sec and MPEG-4 AAC LC audio simultaneously.