C-VCharacterization in MOS Structure Inversion Layer Including Quantum Mechanical Effects

A simplified method to calculate the band bending and subband energy is presented to investigate the Quantum Mechanical Effects (QMEs) in MOS structure inversion layer. The method is fairly unique compared with the published methods in the reversed nature of the iteration procedure. It has high efficiency and good convergence characteristics. Gate capacitance in MOS structure inversion region is formulated in both quantum mechanical cases and semi-classical cases and Quantum Mechanical Effects on gate capacitance have been analyzed. Results of different substrate doping levels are compared and the substrate doping concentration dependence of QMEs on gate capacitance is studied. It is shown that QMEs lead to a substantial decrease in gate capacitance in the strong inversion region. Results of different substrate doping levels indicate that the QMEs on gate capacitance are different substantially in the threshold region at different substrate doping levels but almost the same in the strong inversion region.     

C-VCharacterization in MOS Structure Inversion Layer Including Quantum Mechanical Effects

Ｉｔ ｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｔｈｅｅｌｅｃｔｒｏｎｓｏｆｔｈｅＭＯＳＦＥＴｓｉｎｖｅｒｓｉｏｎｌａｙｅｒｉｓａｃｔｕａｌｌｙ２ＤＥＧｗｉｔｈｓｕｂｂａｎｄｓ,ｅａｃｈｏｆｗｈｉｃｈｃｏｒｒｅｓｐｏｎｄｓａｑｕａｎｔｉ...     

Characterization and modelling of carrier distribution and gate capacitance in MOS structure inversion layer

Based on the carrier distribution in three-dimensional semi-classical and twodimensional quantum mechanical cases, the concept of surface layer effective density-of-states (SLEDOS) is proposed. Then a simplified method of calculating the band bending and subband energies is employed to investigate quantum mechanical effects (QMEs) in MOS structure inversion layer. The method is unique compared with published methods in its reversed nature of the iteration procedure. It has high efficiency and good convergence characteristics and gives satisfactorily coincident results with rigorous but more complicated selfconsistent calculations. The method is applicable in both quantum mechanical and semi-classical cases. The subband occupation of inversion layer carrier and the two-dimensional density-of-states in semi-classical and quantum mechanical cases are then calculated. QMEs on inversion layer carrier density and surface potential are analysed on the basis of the method. Gate capacitance in the MOS structure inversion region is formulated for both quantum mechanical and semiclassical cases, and QMEs on gate capacitance are analysed.     

Region adaptive subband image coding

We present a region adaptive subband image coding scheme using the statistical properties of image subbands for various subband decompositions. Motivated by analytical results obtained when the input signal to the subband decomposition is a unit step function, we analyze the energy packing properties toward the lower frequency subbands, edges, and the dependency of energy distribution on the orientation of the edges, in subband decomposed images. Based on these investigations and ideal analysis/synthesis filtering done in the frequency domain, the region adaptive subband image coding scheme extracts suitably shaped regions in each subband and then uses adaptive entropy-constrained quantizers for different regions under the assumption of a generalized Gaussian distribution for the image subbands. We also address the problem of determining an optimal subband decomposition among all possible decompositions. Experimental results show that visual degradations in the reconstructed image are negligible at a bit rate of 1.0 b/pel and reasonable quality images are obtainable at rates as low as 0.25 b/pel.     

A Functional Analysis Approach to Subband System Approximation and Identification

The subband system identification method consists of identifying a linear system in the time-frequency domain. This technique can be also used to approximate a linear system in the same domain. In both cases, it has the advantage of having a very high numerical efficiency; however, analyzing such a technique is not trivial, and the best setup for subband system approximation and identification is not clear. In this paper, we propose a functional analysis setting to the analysis of the subband technique, which leads us to some results on both subband system approximation and identification. Concerning system approximation, we provide an analytical expression to calculate the optimal subband approximation of a given full-band system, when the quality of the approximation is measured by the power of the output error signal, assuming a white input signal. We also provide a tight approximation error bound, for a given subband configuration, which applies in the case where the unknown system to be approximated is known to be the finite-impulse response (FIR) of a given order. Concerning system identification, we provide a novel identification strategy that consists of identifying a "low quality" subband model and use it to build the required model for either subband or delayless reconstruction. This identification strategy reduces the computational complexity of the identification process and yields significantly smaller asymptotic residual errors, when compared with the existing methods     

Two-dimensional subband transforms: theory and applications

The one-dimensional subband FFT (SB-FFT) and one-dimensional SB-DCT were extended to the two-dimensional (2-D) case to obtain the 2-D SB-FFT and the 2-D SB-DCT. The two-dimensional subband transforms are based on subband decomposition of the input sequence in both dimensions. They use knowledge about the input signal to obtain an approximation to their transform by discarding the computations in bands that have little energy in both dimensions. Computational savings can be obtained from calculating only the remaining subbands. In many applications the computational speed is so important that some error in the calculated transform can be accepted. In image processing, due to the nature of most natural scenes, most of the energy content of the corresponding digitised images is concentrated predominantly in the low-low spatial frequency domain. The concentration of the energy in a localised region of the transform domain makes the approximate subband transform computation quite suitable for the calculation of the 2-D image spectra. The complexity and accuracy of both 2-D transforms are studied in detail in the paper. The approximation errors in both transforms are derived for a general case, in which any band out of M bands is to be computed. Both transforms are modified to be fully adaptive to select the band of interest to be computed. Image transform application examples are included. Savings in computational complexity of image transforms are shown. The efficiency of subband transforms of different images is indicated by computing the signal-to-noise ratio in the reconstructed images.     

An approximate formula for electron energy versus path length

An approximate analytic solution of the Bethe equation for the mean rate of energy loss is derived. This solution is found to deviate by less than one percent from the numerical integration of the Bethe equation for all values of electron path. It is also shown that when the energy-path length relation is expressed in normalized variables, it exhibits only a very weak dependence on material and initial energy.     

Elimination of the electron-phonon interaction in superlattices in a quantizing magnetic field

The energy and wave-vector conservation laws impose rigid constraints on the possible electron-phonon interaction processes in a superlattice immersed in a quantizing magnetic field directed along its growth axis. If the width of the Landau subband is smaller than the maximum energy of an acoustic phonon in the superlattice, single-phonon intraband scattering becomes impossible for all electron states in the subband considered. Therefore, the phonon contribution to the electron scattering processes can become negligible in superlattices with a large period in the presence of a quantizing magnetic field. Fiz. Tekh. Poluprovodn. 32, 730–732 (June 1998)     

Thermoelectric Efficiency of a Quantum Dot in the Single-Electron Transistor Configuration

The thermoelectric efficiency of a single-dot (e.g., nanocrystal or molecule) device has been studied theoretically. The transport coefficients, the power factor, and the figure of merit (ZT) of the quantum dot in the single-electron transistor configuration have been calculated in the sequential tunneling regime when Coulomb blockade is important. Very high values of ZT have been found in the quantum regime, and they have been explained by quantum confinement. An approximate analytical formalism has been derived for ZT as a function of the separation between the energy levels of the dot, ΔE, and the thermal energy, k _B T. The electron–phonon coupling has been included in the calculations, and it is shown that it is important for realistic prediction of the thermoelectric efficiency of a quantum-dot device. It has been found that the thermoelectric efficiency decreases due to electron–phonon coupling. Distinct behavior has been obtained for weak and for strong electron–phonon coupling. Quantum confinement is the dominant mechanism determining the magnitude of ZT for weak electron–phonon coupling. For strong electron–phonon coupling, the energy conversion efficiency is determined by the phonon spectrum. In all cases, it has been found that the thermoelectric efficiency decreases rapidly with increasing temperature.     

Analytical study of a radiating nonlinear electromagnetic crystal under mixing conditions

A nonlinear radiating electromagnetic crystal excited by the plane wave of free space at the signal frequency and the wave of the electromagnetic crystal at the heterodyne frequency is considered. Transformation of the electromagnetic energy of the plane wave into the crystal wave at the intermediate frequency is analyzed. An approximate model of the structure in the form of a system of differential equations is constructed. An analytical solution of this system is obtained. This solution is used to show that the highest efficiency of energy transformation is attained under the conditions of the spatial synchronism of waves at frequencies of the signal and heterodyne and the intermediate frequency.     

Analytic solution of the Feldtkeller equation

In every reflectance-based application like broadband matching, circuit modeling, etc., a nonlinear equation following from energy conservation, the Feldtkeller equation, must be solved, in order to obtain real networks. In the literature, however, there is no analytic solution available but only numerical solutions. Consequently, the resulting error depends on the accuracy of the numerical tools. In this paper, an analytic solution is proposed, which is based on the modified ABCD-parameters of a lossless reciprocal two-port network. An algorithm is presented and examples are included to illustrate the implementation of the analytical method.     

Current Distribution and Impedance of Lossless Conductor Systems

A general method for determining the characteristic impedance of uniform, lossless transmission systems is developed. The torrent distribution within the system is determined by means of a matrix equation programmed for computer solution. Once the current distribution is known, the inductance per unit length and characteristic impedance are determined. The results obtained by applying this method to several rectangular coaxial systems are compared with the predictions of an approximate analytic expression. The reflection coefficient of a variable characteristic impedance coaxial line is measured on a time-domain reflectometer (TDR), and the results are compared with both the matrix method and the approximate analytic expression.     

平面电磁波对双导线传输线终端瞬态响应的求解

随着传输线方法在电磁兼容和电磁干扰分析方面的广泛应用,人们对传输线方程的求解方法也越来越感兴趣.求解传输线方程的方法通常有时域差分方法和频域差分法.而对于平面电磁波对双导线传输线终端的响应,文章给出了其频域解析解,并且运用这个解析解和Fourier变换技术,可以很容易地给出传输线终端的瞬态响应分析.通过数值仿真实验研究三个角度参数φ、α和Ψ在电磁感应中的作用:当φ和α保持不变(或者Ψ和α保持不变),随着Ψ(或者φ)的增大,终端2的感应电流的响应时间缩短,第一阶段的感应时间延长;当φ和Ψ保持不变,随着α的增大,终端2处第一阶段的感应电流也随之减小.     

Four-wave mixing between short optical pulses in semiconductoroptical amplifiers with the consideration of fast gain saturation

With the consideration of fast gain saturation, an approximate analytical solution of nondegenerate four-wave mixing between short optical pulses in a semiconductor optical amplifier is presented. It is simple and agrees well with the rigorous solution. In addition, conditions for the optimum pump input energy and the time delay between the pulses are also investigated     

Analytic modeling of the P-doped cascaded Raman fiber lasers

An approximate analytic model of the P-doped cascaded Raman fiber lasers had been developed. The threshold pump powers for the first and the second Stokes radiation, output power, slope efficiency, and energy conversion efficiency had been solved and thus the optimization of the lasers could be discussed analytically. A fast numerical simulation of the laser based on the analytic model had also been carried out. Moreover, the comparison between the analytic and numerical solution was made.     

Thorough analysis of quantum mechanical effects on MOS structure characteristics in threshold region

Threshold voltage shift due to quantum mechanical effects (QMEs) are studied for both n- and p-MOS structure in the paper. Subband structure and carrier distribution are formulated for both type of MOS structure in effective mass approximation. QMEs on threshold voltage shift are thoroughly analyzed based on the model. Carrier distribution in subbands for both n-MOS and p-MOS are calculated and analyzed from density-of-states point of view. Model results for n- and p-MOS structure are compared with experimental and full-band self-consistent calculation results and show good coincidence. It is proved that at least in threshold region, effective mass approximation has similar accuracy as the full-band self-consistent method to predict the influence of QMEs MOS structure characteristics.     

Dynamic Behavior of a CSMA-CD System with a Finite Population of Buffered Users

In packet broadcast networks with buffered users, queues of packets at the users interfere with each other through a shared broadcast channel. Therefore, it is difficult to analyze the performance of such Systems by classical queueing theory. This paper provides an approximate performance analysis of a slotted nonpersistent CSMA-CD system with a finite number of users, each having a buffer of finite capacity. We develop an approximate Markovian model of the system with a multidimensional state vector. To analyze the model, We utilize an approximate analytical technique called equilibrium point analysis (EPA). Then, the throughput and average packet delay characteristics are obtained and the system stability behavior is demonstrated. An approximate expression is also derived for the probability distribution of the number of packets in a buffer. Numerical results from both analysis and simulation are given to illustrate the accuracy of those analytic results. Using the analytic results, we examine the effect of the collision detection capability on the system performance. Furthermore, we consider how to select both the rescheduling probability and the buffer size that guarantee the system stability, keep the probability of buffer overflow sufficiently small, and at the same time minimize the average packet delay.     

一维光晶格中玻色凝聚气体高斯宽度与光晶格势强度的关系

对囚禁在由谐振势和一维光晶格势构成的组合势中的玻色凝聚气体,基于Gross-Pitaevskii理论,并运用G-P能量泛函和变分方法,研究了组合势中子凝聚体的高斯宽度与光晶格势强度之间的关系.在分析了无相互作用的理想玻色气体的高斯宽度的基础上,提出了考虑相互作用后的高斯近似模型,并求解出高斯宽度随光晶格势强度变化的解析表达式.然后,将所得到的解析结果与直接的数值计算进行比较,表明高斯近似模型与数值计算结果更加接近,并且随着光晶格势强度的增加两者趋于一致.     

Energy efficiency analysis of IEEE 802.15.6 based wireless body area networks in scheduled access mode

This paper investigates the energy efficiency of IEEE 802.15.6 based wireless body area networks in the scheduled access mode. We assume that the hub operates in beacon mode with superframes and the nodes obtain scheduled allocation intervals consisting of finite number of allocation slots from the hub. In this paper, first of all, we present analytical models to compute the energy efficiency of the network for various scheduled allocation and acknowledgement policies assuming ideal channel conditions. The numerical and simulation results show that energy efficiency can be improved by (1) increasing the number of uploads in an active superframe, (2) increasing the payload size, (3) adopting block acknowledgement policy instead of immediate acknowledgement policy or (4) by decreasing the periodicity of allocations. We then present an analytical model to evaluate the energy efficiency in the presence of channel error. An approximate analytical solution for optimal frame size that maximize the energy efficiency of the network in error prone channel is obtained. For each node, we also provide analytical expression for the optimal allocation interval per superframe that maximize the energy efficiency of the network. Through extensive simulation studies, we establish that, in an error prone channel, the energy efficiency can be improved if the nodes make use of computed optimal frame size and optimal allocation interval for the uplink data transfer.     

Charge control model of the double delta-doped quantum-wellfield-effect transistor

The charge control properties of Al_0.3Ga_0.7As-GaAs-Al_0.3Ga_0.7 As quantum-well field-effect transistor (FET) with double δ-doped planes are studied theoretically. A simple capacitor-like charge control model for the doubleδ-doped quantum-well FET's has been proposed and verified through self-consistent calculation. The threshold voltage and the capacitance can be related to the structure through simple analytical equations. The effective separation between capacitor plates is found to be the thickness of AlGaAs layer d+d_i +δ plus a correction term to account for the distribution of N_2DEG inside the GaAs quantum well. For small well widths, only the ground-state subband is occupied and there is a simple linear relation between N_2DEG and the gate bias V_G. For larger well widths, electrons occupied the lowest subband, then the next higher energy subband, and the relation between the N_2DEG and the V_G can be divided into piece-wise linear regions