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.     

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.     

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.     

Saturated inverted transistor modeling for small-signal applications

The modeling and utilization of an inverted integrated n-p-n transistor as a controllable small-signal resistance is explored. A theoretical relation for inverse transistor saturation resistance is developed using a modified Gummel-Poon (G-P) model, and the results are compared to experimental measurements. The relation of inverse beta to the inverse saturation resistance is derived and modeled, as well as the effect of base charge, and bulk resistance. The factors governing the matching of saturation resistance between devices on the same chip and from lot-to-lot are investigated and compared to matching measurements. A noise model for the saturated inverted device is developed and noise measurements appear to confirm the model's validity. Finally, the application of this device to a programmable attenuator circuit is discussed and attenuation and harmonic distortion data are presented.     

Accurate small-signal modeling of HFET's for millimeter-waveapplications

In this paper we discuss the small-signal modeling of HFET's at millimeter-wave frequencies. A new and iterative method is used to extract the parasitic components. This method allows calculation of a π-network to model the heterojunction field-effect transistor (HFET) pads, thus extending the validity of the model to higher frequencies. Formulas are derived to translate this π-network into a transmission line. A new and general cold field-effect transistor (FET) equivalent circuit, including a Schottky series resistance, is used to extract the parasitic resistances and inductances. Finally, a new and compact set of analytical equations for calculation of the intrinsic parameters is presented. The real part of Y₁₂ is accounted for in these equations and its modeling is discussed. The accounting of Re(Y₁₂ ) improves the S-parameter modeling. Model parameters are extracted for an InAlAs/InGaAs/InP HFET from measured S-parameters up to 50 GHz, and the validity of the model is evaluated by comparison with measured data at 75-110 GHz     

A new approach to 3-D modeling of objects with axial symmetry

This paper describes a new method for building a three-dimensional geometrical model of objects from a single image. This method is based on a new concept, namely, the cylindrical projective geometry, which allows us to automatically compute the shape of objects with axial symmetry from one image and without any knowledge about the camera used. Mathematical concepts as well as their use in the modeling process are presented. Some results to show efficiency and accuracy of this method are included.     

A new approach to modeling the substrate current of pre-stressedand post-stressed MOSFET's

In this paper, we propose a closed form expression of a new and accurate analytical substrate current model for both pre-stressed and post-stressed MOSFET's. It was derived based on the concept of effective electric field, which gives a more reasonable impact ionization rate in the lucky-electron model. This effective electric field, composed by two experimentally determined parameters, can be regarded as a result of nonlocal heating effects within devices. This model shows a significant improvement to the conventional local field model. One salient feature of the present model is that it allows us to characterize the time evolution of the substrate current of stressed MOSFET's for the first time. Experimental verification for a wide variety of MOSFET's with effective channel lengths down to 0.3 μm shows that the new model is very accurate and is feasible for any kind of MOS device with different drain structures. The present model can be applied to explore the hot carrier effect in designing submicrometer MOS devices with emphasis on the design optimization of a device drain engineering issue. In addition, the present model is well suited for device reliability analysis and circuit level simulations     

A new approach to the theory and modeling of insulated-gate field-effect transistors

Consideration of basic charge relationships in the IGFET has led to a new formulation of the theory of the device which allows model characterization in a more general manner, and with greater accuracy, than previously achieved. The contribution of the mobile channel charge to the silicon surface potential, which is believed to have a significant influence on the device characteristics, is taken into account in this approach. Accurate device modeling is achieved over a very wide range of operation, extending from weak channel (subthreshold) to high level channel conditions. An important feature of the model is that it is expressed in terms of a constant effective channel mobility. Further, the current and charge relationships involved take the form of a single set of analytic closed-form expressions in terms of the terminal voltages for all conditions of device operation, and are thus appropriate for CAD implementation. The scope and accuracy of this approach to IGFET modeling are demonstrated by comparisons between measured and theoretical dc and small-signal characteristics for sample metal and silicon gate devices.     

A new method for determining the FET small-signal equivalentcircuit

A method to determine the small-signal equivalent circuit of FETs is proposed. This method consists of a direct determination of both the extrinsic and intrinsic small-signal parameters in a low-frequency band. This method is fast and accurate, and the determined equivalent circuit fits the S-parameters well up to 26.5 GHz     

Unified treatment of small-signal space-charge dynamics in bulk-effect devices

Space-charge dynamics in semiconductors with negative differential mobility are discussed in a small-signal approximation taking account of the role of carrier diffusion and are shown to exhibit fundamentally four different properties. These differences originate from two conditions, one being the direction of propagation of the space-charge wave and the other being whether the space-charge wave is characterized by frequency-independent velocity (convective instability) or frequency-independent wavelength (absolute instability). These behaviors of space-charge waves have a great influence on the performance of bulk-effect devices and give rise to extremely different characteristics. When the space-charge wave is characterized by frequency-independent velocity, two-terminal impedance of bulk-effect devices shows the conventional transit-time effect. On the contrary, the property of space-charge waves characterized by frequency-independent wavelength gives rise to the static negative resistance in two-terminal impedance.     

Multibias scalable HEMT small-signal modeling based on a hybrid direct extraction/particle swarm optimization approach

A new multibias HEMT small-signal model extraction method is proposed. The approach, based on scaling rules, combines direct extraction techniques and a particle swarm optimization algorithm. This method has been successfully tested with PHEMTs and MHEMTs, leading to accurate and scalable models up to 70 and 120 GHz, respectively.     

A TCAD approach to the physics-based modeling of frequencyconversion and noise in semiconductor devices under large-signal forcedoperation

The paper presents a novel, unified technique to evaluate, through physics-based modeling, the frequency conversion and noise behavior of semiconductor devices operating in the large-signal periodic regime. Starting from the harmonic balance (HE) solution of the spatially discretized physics-based model under (quasi) periodic forced operation, frequency conversion at the device ports in the presence of additional input tones is simulated by application of the small-signal large-signal network approach to the model. Noise analysis under large-signal operation readily follows as a direct extension of classical approaches by application of the frequency conversion principle to the modulated microscopic noise sources and to the propagation of these to the external device terminals through a Green's function technique. An efficient numerical implementation is discussed within the framework of a drift-diffusion model and some examples are finally provided on the conversion and noise behavior of rf Si diodes