A new small-signal model for asymmetrical AlGaN/GaN HEMTs

A new small-signal model for anisomerous AIGaN/GaN high electron mobility transistors (HEMTs) is pro-posed for accurate prediction of HEMT behavior up to 20 GHz. The parasitic elements are extracted from both cold-FET and pinch-off bias to obtain more precise results and the intrinsic part is directly extracted. All the parameters needed in this process are determined by the device structure rather than optimization methods. This guarantees consistency between the parameter values and the component's physical meaning.     

一种新的兼容栅偏源结构AlGaN/GaN HEMT的小信号模型

本文提出了一种新的AlGaN/GaN HEMT小信号模型,此模型可在20GHz以内对栅偏源结构HEMT进行精确模拟。模型中的寄生参数由零偏及截止两种偏置下的S参数来决定,本征部分采用直接提取的方式得出。本模型中的所有参数及比例系数均由器件结构决定,并不涉及任何优化算法,因而保证了模型参数值与物理意义的统一。     

A simple,direct and reliable extraction method applied to GaN devices

In this article, a simple, direct and reliable extraction method has been developed and applied to different sizes of Gallium Nitride (GaN) high electron mobility transistors (HEMTs). Instead of high-voltage gate-forward measurements with risk of device damage, the proposed approach uses only uncritical cold S-parameters at pinch-off (V_GS < V_p, V_DS = 0 V) and in the off-state (V_GS = 0 V, V_DS = 0 V). The extraction procedure is validated by small- and large-signal measurements. Very good agreement is obtained. Scaling of parasitic elements with the device size is confirmed.     

A new approach to the simulation of small-signal current gains ofpnpn structures

An approach to the mathematical simulation of small-signal current gains (alphas) versus frequency that respects Fulop's measuring procedure is proposed, using an arrangement close to the real measuring circuit. For this purpose, an exact 1-D mathematical model is used. The dependence of small-signal alphas on the anode current of a high power thyristor (GTO) was found to be in agreement with measurements for low anode-to-cathode voltage     

Average and small-signal modeling of self-oscillating flyback converter with applied switching delay

This paper presents a consistent methodology to assess the effect of variable-frequency operation on the dynamics of a flyback converter used in low-cost, high-volume, battery-charger applications. The self-oscillation is typically implemented using peak-current control in boundary conduction mode with a deterministic delay before switching on the next cycle. The modeling is based on the modified state-space-averaging method, where the effect of the varying cycle time and peak-current-mode control is included using special cycle-time and on-time constraints derived from the inductor-current waveforms. The method leads to accurate full-order models, where the effect of the circuit parasitics and the switching delay may also be taken into account. In most of the cases, the effect of parasitics and switching delay is, however, minimal, and therefore, simple small-signal models may be used. The applied switching delay affects the dc operating point in terms of duty ratio and switching frequency, and shall be, therefore, carefully considered.     

A new self-consistent modeling approach to investigating MOSFETdegradation

A modeling tool is presented that allows a complete analysis of a DC stress experiment without assuming the location and amount of trapped oxide charges and interface states. To describe the buildup of oxide damage, a semiempirical rate equation approach is outlined. A completely self-consistent calculation is presented of the time dependence of the DC stress experiment. This calculation monitors the amount and location of charges built up in the 2-D oxide region during the stress line. The model includes competing trap mechanisms such as the formation of interface states and fixed oxide traps. This permits consideration of n- and p-channel MOSFETs with the same model. The calculations are compared to DC stress measurements on n- and p-channel devices with gate lengths of 0.65 μm that are typical for 16-Mb DRAMs     

A new analytical method of solving 2D Poisson''s equation in MOS devices applied to threshold voltage and subthreshold modeling

In this paper we present a new theoretical approach in MOS modeling to derive analytical, physics-based model equations for the geometry and voltage dependence of threshold voltage and for the subthreshold behavior of short-channel MOSFETs. Our approach uses conformal mapping techniques to analytically solve the two-dimensional Poisson equation, whereby inhomogeneous substrate doping is taken into account. The presented model consists of analytical equations in closed form and uses only physically meaningful parameters. Therefore, the results are not only useful in circuit simulators but also in calculations of scaling behavior, where planned processes can be investigated. Comparison with numerical device simulation results and measurements confirm the high accuracy of the presented model.     

Charge-coupled devices? A new approach to MIS device structures

Recent advances in materials and processing have resulted in a new class of information-handling structure?the charge-coupled device. This three-layer structure creates and stores minority carriers, or their absence, in potential wells near the surface of the semiconductor. The minority carriers move from under one electrode to a closely adjacent electrode on the same substrate when a more negative voltage is applied to the adjacent electrode. Because of their high transfer efficiency, these devices have already found application as image sensors. In addition, there is every expectation that memories made by use of the stored-charge concept will be less expensive and faster, and will require less power than a magnetic counterpart now in use.     

基于物理结构的GaN HEMTs小信号等效电路的精确建模方法研究

为了有效地表征GaN HEMTs在微波频段下的电学特性,研究了其高频等效电路的精确建模方法。基于GaN HEMTs器件的本征物理结构,综合考虑器件在制版过程中由电极和通孔所带来的寄生特性,描述了一种具有26个详细参数网络的小信号等效电路模型。此模型考虑了器件在工作环境下所受到的集肤效应,同时通过对小信号等效电路进行双端口网络参数分析,推导了其准静态近似的微波等效电路参数直接提取的简化算法,最终通过ADS仿真平台将所建模型和传统模型的S参数模拟结果与实测数据的一致性进行对比,验证了小信号等效电路模型的精确性与参数提取算法的有效性。     

A NEW ANALYZING APPROACH TO MODELING SLOTTED MULTIPLE ACCESS SYSTEMS

In this paper, the analyzing approaches proposed by Zhao Dongfeng, et al.(1997) have been extensively studied. The average cyclic times of the slotted multiple access systems are analyzed by using the average cycle method. Analytic formulae for mean values of a successful period and a colliding period and an idle period are derived. The upper bounds of the system throughput with capture effect and collision resolution are provided. Finally, the simulation results of the slotted multiple access channels are given.     

AlGaN/GaN HEMT 小信号模型提取方法的改进

The accurate extraction of AlGaN/GaN HEMT small-signal models, which is an important step in largesignal modeling, can exactly reflect the microwave performance of the physical structure of the device. A new method of extracting the parasitic elements is presented, and an open dummy structure is introduced to obtain the parasitic capacitances. With a Schottky resistor in the gate, a new method is developed to extract Rg. In order to characterize the changes of the depletion region under various drain voltages, the drain delay factor is involved in the output conductance of the device. Compared to the traditional method, the fitting of S 11 and S 22 is improved, and fT and fmax can be better predicted. The validity of the proposed method is verified with excellent correlation between the measured and simulated S-parameters in the range of 0.1 to 26.1 GHz.     

A novel small-signal equivalent circuit model for GaN HEMTs incorporating a dual-field-plate

An accurate and novel small-signal equivalent circuit model for GaN high-electron-mobility transistors (HEMTs) is proposed, which considers a dual-field-plate (FP) made up of a gate-FP and a source-FP. The equivalent circuit of the overall model is composed of parasitic elements, intrinsic transistors, gate-FP, and source-FP networks. The equivalent circuit of the gate-FP is identical to that of the intrinsic transistor. In order to simplify the complexity of the model, a series combination of a resistor and a capacitor is employed to represent the source-FP. The analytical extraction procedure of the model parameters is presented based on the proposed equivalent circuit. The verification is carried out on a 4 × 250 μm GaN HEMT device with a gate-FP and a source-FP in a 0.45 μm technology. Compared with the classic model, the proposed novel small-signal model shows closer agreement with measured S-parameters in the range of 1.0 to 18.0 GHz.     

Techniques for small-signal analysis of semiconductor devices

Techniques for ascertaining the small-signal behavior of semiconductor devices in the context of numerical device simulation are discussed. Three standard approaches to this problem will be compared: (i) transient excitation followed by Fourier decomposition, (ii) incremental charge partitioning, and (iii) sinusoidal steady-state analysis. Sinusoidal steady-state analysis is shown to be the superior approach by providing accurate, rigorously correct results with reasonable computational cost and programming commitment.     

Improvements to the extraction of an AlGaN/GaN HEMT small-signal model

The accurate extraction of A1GaN/GaN HEMT small-signal models, which is an important step in large-signal modeling, can exactly reflect the microwave performance of the physical structure of the device. A new method of extracting the parasitic elements is presented, and an open dummy structure is introduced to obtain the parasitic capacitances. With a Schottky resistor in the gate, a new method is developed to extract R_g. In order to characterize the changes of the depletion region under various drain voltages, the drain delay factor is involved in the output conductance of the device. Compared to the traditional method, the fitting of S_(11) and S_(22) is improved, and f_T and f_(max) can be better predicted. The validity of the proposed method is verified with excellent correlation between the measured and simulated S-parameters in the range of 0.1 to 26.1 GHz.     

A new approach to the modeling of converters for SPICE simulation

An approach to the modeling of DC-DC converters for SPICE simulation is developed in which the average current in the energy-storage inductor is first simulated in a SPICE subcircuit for both the continuous and discontinuous modes of operation. The inductor current is then weighted and redistributed to related branches of the circuit to simulate the average input and output currents of the converter. Based on this technique, various converter models, including that of the Cuk converter with coupled inductors, which are valid for both continuous and discontinuous modes of operation, are developed     

A physically based small-signal circuit model for heterostructureacoustic charge transport devices

A physically based small-signal circuit model for GaAs-AlGaAs Schottky gate heterostructure acoustic charge transport (HACT) devices is presented. Analytical expressions for the instantaneous and average channel current as a function of gate voltage are obtained from physical device parameters. The charge injection model is based on subthreshold current models for GaAs MESFETs. It is shown that the shape of the sampling aperture of the charge injection operation is approximately Gaussian. Good agreement is obtained between the measured DC channel current versus gate voltage and that predicted by the model. Equivalent circuits for the transfer and output sensing operations and expressions for noise sources due to the physical processes that occur within the device are developed. Thermal, shot, and transfer noise are treated. The form of the analytic expressions for frequency response and noise figure allows easy implementation on commercially available CAE software. Simulations of both gain and noise figure performed on Libra show good agreement with measured data     

Image modeling and restoration: A new approach

In this paper a new method to image restoration problems is proposed. The main result is the definition of an image model which does not require knowledgea priori of the image autocorrelation function or the use of identification estimation algorithms. The basic hypothesis is that the image can be modeled as an ensemble of two-dimensional differentiable surfaces. In this case the signal and its partial derivatives with respect to the spatial coordinates can be assumed to be the state vector and an image state space representation is directly obtained. A semicausal dependence model is adopted, it is embedded in a strip recursive scheme suitable to the Kalman filter application. Numerical results, concerning three different kinds of images, show high performances of the algorithm.     

一种HEMT器件可缩放的非线性紧凑模型

提供了一种应用于高电子迁移率晶体管(HEMT)的非线性紧凑模型。该模型针对传统的EE-HEMT模型理想缩放规律不准确的问题,提出采用一元函数拟合、二元曲面拟合方法,对其尺寸缩放和温度缩放规律进行修正。修正后的非线性模型可以准确地模拟HEMT器件的直流I-U、S参数和大信号特性。并将该模型应用于一款0.25 μm栅长的GaAs pHEMT工艺,对比不同尺寸的器件在高低温条件下模型仿真结果和实测结果,两者吻合良好,验证了该模型的准确性。