A graded-gap photoelectric detector for ionizing radiation

A heterostructure consisting of a graded-gap p-Al_xGa_1?xAs layer on an n-GaAs substrate is studied in relation to its role as a photoelectric-response detector of X-ray photons and α particles. It is found that the current-power sensitivity of the detector is as high as 0.13 A/W and the voltage-power sensitivity exceeds 10⁶ V/W. The effect of preliminary irradiation with 5.48-MeV α particles (²⁴¹Am) on the detector’s sensitivity is studied. It is established that the detector’s sensitivity is reduced by a factor of 1.5–2 after irradiation with α particles at a dose of 5 × 10⁹ cm^?2. A further increase in the radiation dose to 4 × 10¹⁰ cm^?2 does not affect the detector’s sensitivity.     

A graded-gap detector of ionizing radiation

The current response of Al_xGa_1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick Al_xGa_1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of Al_xGa_1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap Al_xGa_1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×10³ V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.     

A simplified model for subpinchoff conduction in depletion-mode IGFET's

An expression is developed for theI-Vcharacteristics of a depletion-mode device in the subpinchoff region. This expression is found to correlate well with experimental results taken on n-channel polysilicon gate devices, predicting a region of exponential current rise with gate voltage. It is of interest to note that the subpinchoffI-Vcharacteristics of a depletion-mode device form a dual to those of an enhancement-mode device.     

A simplified and more general model for waveguide laser resonators

The model of R. Gerlach et al. (ibid., vol.20, no.8, p.948-63, 1984) is generalized to analyze waveguide laser resonators with curved mirrors and multiple waveguide modes. The analytical expressions obtained permit a considerable computation time reduction and allow a systematic study of the influence of different parameters. As a result, the existence of new structures with low losses appears to be possible     

A model for laterally graded Cu2S/ZnxCd1-xS photovoltaic heterojunctions

A model is presented for the Cu₂S/Zn_xCd_1-xS heterojunction that is based on the existence of a laterally graded zinc rich region just below the Cu₂S-ZnCdS interface. Integrals for short circuit current density and current density versus applied voltage are presented. The current-voltage characteristics, in particular the increase in open circuit voltage and decrease in short circuit current density that occur with increasing zinc content, follow trends that have been seen experimentally for junctions formed by ion-exchange. Supported by the Solar Energy Research Institute.     

A simplified model of a TRAPATT diode

A simplified computer model of a TRAPATT (trapped plasma avalanche triggered transit) diode was developed and is used to investigate realistic voltage-current waveforms (i.e., waveforms that produce negative conductances at all signal frequencies). Oscillator efficiency variations due to fundamental and second-harmonic current tuning were studied. The computed waveforms show good agreement with the TRAPATT waveforms obtained experimentally.     

A simplified broad-band large-signal nonquasi-static table-basedFET model

In this paper, a simplified nonquasi-static table-based approach is developed for high-frequency broad-band large-signal field-effect-transistor modeling. As well as low-frequency dispersion, the quadratic frequency dependency of the γ-parameters at high frequencies is taken into account through the use of linear delays. This model is suitable for applications related to nonlinear microwave computer-aided design and can be both easily extracted from dc and S-parameter measurements and implemented in commercially available simulation tools. Model formulation, small-signal, and large-signal validation will be described in this paper. Excellent results are obtained from dc up to the device f_T frequencies, even when f _T is as high as 100 GHz     

Prediction of band discontinuities in semiconductor heterojunctions: A simple model

A simple model for the prediction of heterojunction valence band discontinuities is proposed in this paper. Only two properties of semiconductors are used in this model, namely the lattice constant and the energy gap.     

AlGaAs and GaAsP high-power ultrafast p+-n-n+diodes based on heterojunctions and a graded-gap base

The authors present a theoretical model of power p⁺-n-n ⁺ diodes with a graded-gap base and either homojunctions (GB) or heterojunctions (HGB), and numerical calculations of static and dynamic characteristics of AlGaAs (GaAsP) based structures. It is shown that HGB diodes will exhibit characteristics and properties significantly better than those of simple (homojunctions plus uniform base) GaAs and Si diodes. For example, the forward voltage drop in a high-voltage (W/L_p=13) high-frequency (t_rr=25 ns) HGB diode will be 50% and 300% smaller than the drop in, respectively, simple GaAs and Si diodes with the same W/L_p and t_rr. Other significant projected improvements include operation up to 450°C, an order of magnitude reduction in the reverse current, and a 50% increase in the breakdown voltage     

A simplified energy consumption model for fiber-based Next Generation Access Networks

ICTs account nowadays for 2% of total carbon emissions. However, in a time when strict measures to reduce energy consumption in all the industrial and services sectors are required, the ICT sector faces an increase in services and bandwidth demand. The deployment of Next Generation Networks (NGN) will be the answer to this new demand and specifically, the Next Generation Access Networks (NGANs) will provide higher bandwidth access to users. Several policy and cost analysis are being carried out to understand the risks and opportunities of new deployments, though the question of which is the role of energy consumption in NGANs seems off the table. Thus, this paper proposes a model to analyze the energy consumption of the main fiber-based NGAN architectures, i.e. Fiber To The House (FTTH) in both Passive Optical Network (PON) and Point-to-Point (PtP) variations, and FTTx/VDSL. The aim of this analysis is to provide deeper insight on the impact of new deployments on the energy consumption of the ICT sector and the effects of energy consumption on the life-cycle cost of NGANs. The paper presents also an energy consumption comparison of the presented architectures, particularized in the specific geographic and demographic distribution of users of Spain, but easily extendable to other countries.     

A simplified functional simulation model for three-phasevoltage-source inverter using switching function concept

In this paper, a functional simulation model for the voltage-source inverter (VSI) using the switching function concept is studied and the actual implementation of the model is proposed with the help of Matlab Simulink. Also, this concept is extended to the voltage-doubler-type pulse width-modulated (PWM) AC-DC rectifier and the PWM AC-DC-AC converter. With the developed functional model, the simplification of the static power circuits can be achieved so that the convergence and long run-time problems can be solved. Also, in the functional model, the design parameters, such as voltage and current ratings of the power semiconductor switches and load current, can be easily calculated. The general switching function concept is reviewed in brief and the proposed functional models for the VSI, voltage-doubler rectifier, and PWM AC-DC-AC converter and their implementations using Matlab Simulink are explained in detail. Also, several informative simulation results verify the validity of the proposed models     

A simplified model for the static characteristics of amorphous silicon thin-film transistors

A simplified and more accurate expression for the static I_D − V_D characteristics of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFT) has been derived. The results show that the experimental drain characteristics agree very well with the derived equations. This model shows its greatest improvement over other models at low values of gate voltage and at large values of drain voltage. The model is based on the experimental function for the channel conductance vs gate voltage. Four constants, obtained from the experimental data of I_D vs V_G at some small value of V_D, are used to completely specify the simplified model. The theoretical results confirm the simple form of the model in terms of the device geometry. The constants calculated from the theory agree well with those extracted from the conductance data.     

A simplified analytic CAD model for linearly tapered microstrip lines including losses

Quasi-TEM propagation, appropriate for a linearly tapered microstrip line is modeled, and known microstrip impedance behavior is approximated directly. The telegraphist's equations and the resulting ABCD matrix are solved in terms of Airy functions. The theoretical model, which includes conductor and substrate losses, has been verified experimentally.     

A simplified model for interpreting the Doppler spectrum of forward-scatter radar signals

An approximate form of Birkemeier's anisotropic scattering function is developed. This Gaussian scattering model is meant to be used for interpreting the Doppler Spctra of signals taken from a forward scatter radar system equipped with a Rake receiver. The model offers advantages in extracting the anisotropy coefficient from the Doppler spectrum of the received signal.     

A simplified analytical model for predicting path loss in urban andsuburban environments

An analytical propagation model has recently been developed to predict radio signal attenuation in urban and suburban environments. This analytical model explicates the path loss as a result of signal reduction due to free space wavefront spreading, multiple diffraction past rows of buildings, and building shadowing. It is applicable for cellular mobile services as well as personal communications services (PCS) in both macro- and microcellular environments. Good accuracy was found for this analytical model by comparing the predictions with numerous measurements made in various propagation environments. However, since the analytical model involves multiple-dimension integration to calculate the signal attenuation due to multiple diffraction past rows of buildings, the model in its original format does not lend itself to easy implementation into a radio system planning tool. A simplified version of the analytical model is developed in this paper, which can be used for three different propagation scenarios with base-station antenna above, below, and near the average rooftop level     

A simplified and efficient numerical model for charge injection inacoustic charge transport devices

A numerically efficient model for simulating electrical charge injection in acoustic charge transport (ACT) devices is developed. This model simplifies an existing charge injection model and is derived using the coupled set of semiconductor device equations. The present model increases the computational efficiency of decoupling and reducing the number of mathematical equations forming the charge injection model. A brief overview of the original model is presented. The assumptions leading to the decoupling and reduction of the device equations are described, as are differences between the two models. Results computed by the simplified model are shown and compared to the results from the original charge injection model and experimental measurement. The present model is able to examine 45 SAW wave positions and 163 contact voltages in 8 h on a 25 MHz PC in comparison to the previous model which simulated 59 wave positions and 164 contact voltages on an Hewlett-Packard 9000 series 500 minicomputer in 37 h. A substantial reduction in computation time is achieved     

A new simplified two-dimensional model for the threshold voltage ofMOSFET's with nonuniformly doped substrate

A new simplified two-dimensional model for the threshold voltage of MOSFETs is derived in terms of simple characteristic functions. These characteristic functions are transformed from the exact series solution of the two-dimensional Poisson's equation, in which the effects of a nonuniformly doped substrate and a finite graded source-drain junction depth are included. In this model, charge-screening effects are proposed to account for the weak dependence of the threshold voltage on the substrate bias for short-channel MOSFETs, and exact source and drain boundary potentials can be approximated by their equivalent power functions. The accuracy of the simplified 2-D model is verified by 2-D numerical analysis. Moreover, comparisons between the simplified 2-D model and the experimental results are made, and good agreement is obtained for wide ranges of channel lengths, applied substrate, and drain biases     

A geometry based simplified analytical model of switched reluctance machines for real-time controller implementation

A geometry based simplified analytical model that decouples the current and position effect on flux and torque in the switched reluctance motor (SRM) drives is presented in this paper. This model gives a direct relation between phase current and torque accounting for the high degree of nonlinearity of the machine. A simple flux model and its inverse relationship have been developed to meet the diverse requirements of controller design. The paper emphasizes and demonstrates the importance of these relationships for real time controller implementation of high performance SRM drives.     

一种简化的多阶段译码结构

通过分析MSD和PDL两种译码方法在等价调制容量计算上的异同点及其与映射方法之间的关系，提出了几种新的针对8PSK和16QAM的信号星座映射图，按此进行映射设计，可以将MSD译码结构部分地用并行结构来实现，从而简化了系统的译码算法，降低了系统的译码时延。仿真结果表明：改进的MSD结构不会带来系统在性能上的损失，相反在低信嗓比情况下，由于错误传播现象的消除而使系统的性能有所提高，结果可直接推广到其它高维MPSK和MQAM信号空间。