Noise in DMOS transistors in a BICMOS-technology

An experimental and theoretical study of the 1/f noise and the thermal noise in double-diffused MOS (DMOS) transistors in a BICMOS-technology has been carried out. By using an analytical model that consists of an enhancement MOS transistor in series with a depletion MOS transistor and a resistance, and by attributing noise sources to each device, the noise in DMOS devices is simulated accurately. Three distinct regions of operation are defined: enhancement transistor control, depletion transistor control and the linear region. In the first region, the noise is strictly determined by the enhancement transistor. It was found that the 1/f noise in this region is caused by mobility fluctuations and is very low. In the depletion transistor control region both transistors influence the total noise. Here the 1/f noise is dominated by the depletion transistor. The series resistance is only of importance in the linear region     

Achieving Competence-Based Curriculum in Engineering Education in Spain

The fact of placing competences and outcomes learning at the heart of the academic activity means overhauling the curricular architecture of higher education in Europe. Some universities have undergone important transformations moving toward a competence-based learning environment, while others maintain traditional curriculum packaged formats. In the realm of the European Higher Education Area, this paper examines the use of competence-based initiatives in curricular development for engineering degrees with special focus to the Spanish case. Although the concept of competence and competence-based learning has a long history in education and training research, these terms are still very diffuse and demand a clear conceptualization. In the first part of this paper, we provide a conceptual overview and a critical reflection of competences as implemented in a wide range of settings, including its origins, key concepts, and definitions. Next, we discuss the purposes, principles, pitfalls, and processes that enable defining a map of competences within engineering education. Lastly, we present a pilot project involving curriculum development and faculty enhancement within a competence-based learning initiative in electronic engineering.     

Telecommunications in Malaysia: diversity in adversity

The telecommunications industry in Malaysia has experienced a tremendous transformation in just over a decade. The government-owned Jabatan Talikom, which hitherto operated the network, was incorporated in 1987 and subsequently privatized a few years later, with a majority share holding by the government. The regulatory aspects were spun off under the slim looking JTM. This marked the beginning of liberalization, and many new players entered the fray. This article reviews the telecommunications infrastructure and services available in Malaysia and visits some of the telcos offering these services. Some pertinent issues affecting the industry are also discussed     

Traces in proximity to gaps in return planes

Coupling between circuitry on printed circuit boards can be mitigated by a variety of well-known techniques. One such technique is to isolate circuitry in different areas of the printed circuit board by strategically placing a gap in the signal return plane. However, this technique is only effective at reducing common-impedance coupling, which is generally not a significant coupling mechanism at frequencies above 1 MHz. This paper investigates the effect of a gap located between and parallel to adjacent microstrip traces. The effect of the gap on the mutual inductance and mutual capacitance is evaluated. Laboratory measurements and numerical simulations show that gaps in the return plane are ineffective at reducing inductive and capacitive crosstalk in most configurations, and in some cases they increase the mutual coupling between printed circuit board traces.     

Physical processes in duplexer discharges in chlorine and oxygen

The high-power properties of the input-window discharge of a TR tube are analyzed in terms of the transmission and reflection coefficients of a thin plasma slab terminated by a low-intensity secondary gap discharge. Computer solutions were obtained for equations expressing the TR properties of arc loss, leakage power, recovery time, and phase shift as functions of collision frequency and electron density. Measurements of arc loss and leakage power in a chlorine discharge yielded values of electron density of 1 × 10¹⁴to 6 × 10¹³electrons/cm³over a 0.5- to 80-torr pressure range. The recovery period atX-band corresponds to a decaying plasma in which electron density decays from 10¹⁴to 10¹²electrons/cm³. This decay occurs in less than 0.5 µs for chlorine discharges. An analysis of the physical mechanisms controlling fast recovery times in electronegative gases shows that the two most important physical mechanisms are recombination of electrons and ions in the early recovery period and electron attachment in the late recovery period. Experimental data is presented for the recovery of chlorine and oxygen over a pressure range of 0.5 to 80 torr. An analysis of measured values of attachment frequency in oxygen indicates that the electron temperature in the recovery period, which is early in the afterglow, was in the 1.4- to 1.2-eV range.     

Polariton condensate coherence in planar microcavities in a magnetic field

In planar GaAs microcavities in a magnetic field up to 5 T perpendicular to the structure growth plane, under conditions of resonant pulsed pumping to a point close to the inflection point of the lower dispersion curve, Zeeman splitting of the spin sublevels of the polariton condensate is observed. This is accompanied by a significant change in the degree of circular polarization and the second-order correlator g²(0). It is found that the correlator is different for the spin sublevels of the polariton condensate, split in a magnetic field. In particular, correlator measurements indicate different condensation thresholds for the spin sublevels. The correlator values initially differing in terms of the absence of a field increase, reach a maximum, and then decrease and become equal for different polarizations in a field of 5 T.     

Electron mobility in two-dimensional electron gas in AIGaN/GaN heterostructures and in bulk GaN

We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm²/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm²/Vs compared to approximately 1200 cm²/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.     

Two-wave mixing in reflection holograms in photorefractivematerials

The intensity and phase of two counterpropagating optical beams in a photorefractive material are investigated both numerically and by using an approximate analytical theory. It is shown that in the reflection regime they are two situations where coupling between the beams may be spatially dependent; in the case of nearly degenerate two-wave mixing, and when a photocurrent is present. In these situations, previously obtained results may need significant correction     

Fission of longitudinal autosolitons in InSb in a magnetic field

The behavior of longitudinal autosolitons in InSb in a weak magnetic field was studied. It is shown experimentally that a weak longitudinal magnetic field affects significantly the behavior of longitudinal autosoliton in InSb samples. In all samples, sharp changes in the current due to fission of longitudinal autosoliton were observed for certain values of a magnetic field. It was found that the magnitude of initial autosoliton cur-rent took a different stable value under the effect of a magnetic field. The initial value of the autosoliton current is recovered if a magnetic field of opposite orientation is applied to the sample.     

Advances in millimeter-wave subsystems in Japan

The authors describe the development trends and results of millimeter-wave systems in Japan in such fields as communication, radar, and measurement systems. The applications included are the W-40G waveguide transmission communication system, an automobile traffic control system using the 60-GHz band, a collision avoidance radar system for an automobile, a plasma electron density measuring system, and satellite communication. The authors describe the development of devices such as high-power FET amplifiers, traveling wave tube amplifiers (TWTAs), IMPATT amplifiers, low-noise amplifiers, and monolithic microwave integrated circuit (MMIC) devices used in constructing the millimeter-wave systems     

Noise effect in oscillators using multiple active devices connected in series or in parallel

The effect of noise in an IMPATT or Gunn diode oscillator on a phase or frequency fluctuation can be reduced when the oscillator is constructed of multiple diodes connected in series, compared with the oscillator using a single diode.     

The Measurement of the Change in Productivity in Telecommunications

The use of incentive regulation in telecommunications in the United States requires accurate measurement of the change in productivity. An approach to measuring productivity change, the Malmquist index approach, is introduced that not only provides a measure of that change but also allows for a decomposition into two mutually exclusive and exhaustive components – changes in technical efficiency over time and shifts in technology over time. Using annual data on four output measures and six input measures for the period 1988–1999 for nineteen local exchange carriers, the results indicate that productivity increased by about 5.5% per year. This growth is due primarily to innovation rather than improvements in efficiency. Of the nineteen LECs in the sample, eleven were operating efficiently throughout the entire 1988–1999 period. Of the remaining eight, four showed a slight improvement in efficiency while the efficiency of four declined. In the aggregate, however, there was virtually no change in efficiency. Finally, a comparison is made between two methods of estimating the change in productivity. The conventional growth accounting approach yields a lower estimate of the rate of change in productivity than does the Malmquist index approach.     

Interband light absorption in size-confined systems in uniform electric fields

A simple approach to calculation of the interband absorption coefficient in a uniform electric field is developed. This approach provides a means for studying the special features of electroabsorption in a wide class of semiconductor systems on the basis of the most general relationships. The approach is used to study the electroabsorption in two-dimensional systems with different profiles of their one-dimensional potential, quantum wells, and superlattices in magnetic fields.     

The current in a parasitic antenna in a dissipative medium

A relatively simple analytic formula is derived for the current in a bare conducting cylinder of length2hand radiusawhen embedded in an isotropic homogeneous dissipative medium and excited by a periodic electric field with uniform amplitude and phase along its axis. In the derivation the same approximations are made as in an earlier analysis of the center-driven antenna for which complete experimental verification has been obtained. Computations are reported specifically for an antenna immersed in the ocean and excited by a field of very low frequency. The principal parameter ish/lambdain the range from 0.03 to 0.23 at a frequency of 5 Hz, wherelambdais the wavelength in sea water. The effect of changes in the radiusaare also shown successively witha/lambdaandh/aas the variable parameter. When the results of this paper are combined with those for the center-driven element, they provide the means for determining the response of a center-loaded dipole receiving antenna when immersed in a dissipative medium. Such an antenna is of interest in problems that relate to communication with submerged submarines and off-shore facilities.     

On the electromagnetic field in a cavity fed by a tangentialelectric field in an aperture in its wall

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity     

Switching conduction in ion-irradiated layers in GaAs

Experiments have been performed to investigate whether switching phenomena are observable in ion-irradiated GaAs. It is found that the V/I characteristics of H2+-and N+-irradiated layers show both negative resistance and switching from a high resistance to a low resistance state. Ion irradiation may thus be a useful method of fabricating switching devices.     

Powerless in Gaza

In november of 2008, the backup batteries unexpectedly failed at a power plant in the Gaza Strip. Almost anywhere else, the incident would have been a blip, forgotten a week later. But this is Gaza-blockaded by Israel and Egypt and cut off from the Palestinian National Authority in the West Bank. It's a place where more than a million and a half people inhabit a strip of land not even one?third the size of the city of Los Angeles... and where there is only one power plant.     

Hot electron transport in high-lying minibands in semiconductor superlattices

We describe the first measurements of hot-electron transport in a semiconductor superlattice. The structures we have studied are three-terminal devices consisting of a superlattice sandwiched between a tunnel barrier injector on one side and an energy spectrometer on the other. These structures offer the unique flexibility of being able to inject carriers of arbitrary energy into the superlattice bandstructure and perform hot-electron spectroscopy on the carriers that have traversed the superlattice.

We demonstrate that hot electron transport is possible in high-lying minibands (the second, third, and fourth) through the appearance of a well defined peak in the analyzed energy distribution. In addition, from the transfer function characteristic, we prove that the electrons are transporting coherently: that is, they obey the miniband dispersion relation. Finally, we describe a model for the electron transport.     

移动环境下LBS位置隐私保护

用k匿名模型对基于位置信息的服务(LBS)中的位置隐私进行保护是近年来研究的热点。在移动用户不断发出查询的场景下,该文提出了移动模式攻击(MPA),使得传统的针对孤立查询的隐私保护算法均失效。基于熵理论,提出了熵匿名度度量,并以此为基础提出了移动环境下的模糊化算法Mclique,实验证明其有效地抵御了MPA攻击。通过简化Mclique算法中熵的计算,提出了快速模糊化算法Fclique,实验证明Fclique不仅仍具有较强的MPA抵御能力,且极大提高了时间效率。     

2002年西欧电信市场回顾

2002年，欧盟颁布了新的电信管制和关于发展的一系列指令，另外还专门成立了一个欧洲管制机构小组来加强各成员国管制机构的协调和统一。2002年．欧洲电信市场的增长开始出现停顿；固定电话市场第一次出现下滑；移动业务依然占据通信产业的最大份额但增长速度放慢；数据业务收入有所下降，但是互联网和宽带接入的增长仍然让人鼓舞等。尽管运营商状态不佳．很多传统运营商为前几年向国际扩展付出了沉重代价．但是欧洲也形成了一批新的泛欧运营商，这将大大影响各个市场的发展趋势和竞争状况。