Measurements of the velocity of plasma spread in switched thyristors

The method employed in the measurement of plasma spreading velocity ν_s, in power thyristors and the results obtained are reported in detail. To induce ν_s to be primarily one-dimensional the thyristors wore rectangular in configuration with gate contacts to measure the arrival of the plasma, being placed at regular intervals around the rectangular (alloyed) cathode. Gold-doped devices were compared with geometrically similar thyristors nominally gold free. Values of ν_s for gold-doped thyristors were persistently, though not always, lower. The current gain of the constituent transistors has also been measured and attempts are made to correlate these to the measured ν_s values. The currant, gains, particularly of the n-p-n section, prevailing in the ‘ off ’ region of a thyristor during a switch-on transient are contrasted with those obtaining during current gain measurements and are thought to be responsible, in conjunction with the lowered life-time in the wide n-basr regoin of the p-n-p section, for the lowered ν_s values of gold-doped thyriators.     

A simple model for flux weakening in surface PM synchronous machines using back-to-back thyristors

Flux weakening in surface permanent magnet (PM) synchronous machines is revisited in this letter. The condition for achieving infinite constant power speed ratio (CPSR) is explained from the machine equivalent circuit and phasor diagram point of view. Back-to-back thyristors, or triac, switches feeding the three phases of a surface PM synchronous machine will be shown to be equivalent to a simple series reactance with respect to fundamental component behavior. Using such switches is equivalent to adding a series inductance to the machine. This additional inductance helps extend the CPSR of surface PM synchronous machines. This is significant because extending the CPSR of surface PM machines is usually a challenging task due to the presence of low-permeability surface magnets and the resulting low machine inductance.     

Probed determination of turn-on spread of large area thyristors

Thyristors (SCR's) were specially constructed to permit the direct observation of the lateral spread of turn-on within the device. The effects on the spread of turn-on of the load current, basewidths, temperature, anode-cathode voltage, gate control pulse, and a large inhomogeneity were observed. The spreading velocity of the on-state and the load current are related approximately by the expressionV^{n} propto Iat high load currents. The spreading velocity is higher in devices with narrower basewidths and increases with temperature. Neither the anode-cathode voltage before turn-on nor the gate control pulse affect the spreading velocity of the on-state. Measurements on end gate devices and center gate linear devices show that triggering at the center enables an equivalent area of the SCR to turn on in less time than occurs when triggering at the end. A large gap in the emitter layer will delay the spread of the on-state but will not necessarily stop the spreading.     

Plasma spread in high-power thyristors under dynamic and static conditions

The plasma spread properties of various thyristors were studied utilizing an infrared viewing technique. The plasma velocity occurring prior to equilibrium, and plasma spread conditions at equilibrium were determined. Velocity versus current density diagrams were generated for low-frequency, high-voltage and high-frequency, low-voltage devices. Effect of the initial turned-on line on plasma spreading is discussed.     

Quasi-three-dimensional spice-based simulation of the transient behavior, including plasma spread, of thyristors and over-voltage protectors

This paper describes a fast and reliable circuit-based simulation method of two-dimensional electrical transient characteristics of thyristors and over-voltage protectors (TOVP). Either device is divided into four-layered square prisms, and a one-dimensional PNP–NPN transistor pair model associated to each of them. The transistors are represented with the Gummel–Poon model, complemented with breakdown and quasi-saturation sub-models. The cells in turn are coupled through the base planes, with current-modulated resistors. Plasma-spreading velocities obtained through simulation are comparable to experimentally obtained ones reported elsewhere. Spatial current density instabilities induced by device asymmetries are also presented. The required spatial resolution was attained by representing these four-layer devices with up to 40,000 Spice circuit elements, including 3000 bipolar junction transistors. The associated Spice lists were assembled effortlessly with a Mathematica program. Simulations took from 1 to 3 h in a 650 MHz Pentium III computer, with no symptoms of convergence problems whatsoever. The authors believe this is the first time that Spice based high-resolution transient behavior simulations of TOVPs and thyristors are presented in the literature.     

A fast and exact time-domain simulation of switched-mode powerregulators

A new approach for the time-domain simulation of switched-mode power regulators is developed. The concept of this approach is to model each switch element by a linear time-varying nodal equation, thus formulating a modified nodal equation system that describes the global dynamic behavior of the power regulator. By using the symbolic Laplace transform inversion, the time-domain expressions can be obtained in a closed and continuous form, which allows a fast and exact simulation of the system. The time efficiency of the proposed approach is shown by comparing it with a standard numerical integration method. Various transient responses of a practical switched-mode power regulator due to the start-up, the step change in input voltage, and the step change in reference voltage have been simulated. The simulations include the overcurrent protection limitation, the duty-cycle limitation control, the discontinuous conduction mode, and the continuous conduction mode of operation     

A time-domain digital cochlear model

The author presents a digital time-domain model of the human cochlea designed to represent normal auditory functioning and to allow for degradation related to auditory impairment. The model consists of the middle ear, the mechanical motion of the cochlea, and the neural transduction of the inner hair cells. The traveling waves on the cochlear partition are represented by a cascade of digital filter sections, and the cochlear micromechanics are represented by a second filter that further sharpens the excitation to the inner hair cells. The neural firing rate is determined by the sum of the outputs of multiple fibers attached to each inner hair cell, with the fiber neurons having firing characteristics representative of low- and high-spontaneous-rate fibers. The signal processing cochlear model incorporates dynamic-range compression by adjusting the Q of each cochlear filter section and second filter in response to the second-filter velocity and the averaged neural firing rate. Examples of the model response to impulse and tone-burst stimuli and to synthetic speech are presented     

A fast time-domain finite element-boundary integral method forelectromagnetic analysis

A time-domain, finite element-boundary integral (FE-BI) method is presented for analyzing electromagnetic (EM) scattering from two-dimensional (2-D) inhomogeneous objects. The scheme's finite-element component expands transverse fields in terms of a pair of orthogonal vector basis functions and is coupled to its boundary integral component in such a way that the resultant finite element mass matrix is diagonal, and more importantly, the method delivers solutions that are free of spurious modes. The boundary integrals are computed using the multilevel plane-wave time-domain algorithm to enable the simulation of large-scale scattering phenomena. Numerical results demonstrate the capabilities and accuracy of the proposed hybrid scheme     

A method for fast time-domain simulation of networks with switches

A method for fast time-domain simulation of piecewise-linear networks with switches is described in this paper. The method is based on a discrete-time switch model that consists of a constant conductance in parallel with a current source. In each simulation step, the value of the current source is updated as a function of known network signals. The function takes one of two forms, depending on the state (on or off) of the switch. Since the system matrix is constant, regardless of the states of the switches, simulation time is essentially the same as for a linear, time-invariant network of the same complexity. The paper discusses selection of the model and simulation parameters. The simulation algorithm is described and an example is included. It is shown that the method is not only efficient but also quite general and void of convergence problems. Its primary application is for long-term transient simulation of power electronic systems such as switching power converters     

Human body model electrostatic discharge tester using metal oxide semiconductor-controlled thyristors

Electrostatic discharge (ESD) testing for human body model tests is an essential part of the reliability evaluation of electronic/electrical devices and components. However, global environmental concerns have called for the need to replace the mercury-wetted relay switches, which have been used in ESD testers. Therefore, herein, we propose an ESD tester using metal oxide semiconductor-controlled thyristor (MCT) devices with a significantly higher rising rate of anode current (di/dt) characteristics. These MCTs, which have a breakdown voltage beyond 3000 V, were developed through an in-house foundry. As a replacement for the existing mercury relays, the proposed ESD tester with the developed MCT satisfies all the requirements stipulated in the JS-001 standard for conditions at or below 2000 V. Moreover, unlike traditional relays, the proposed ESD tester does not generate resonance; therefore, no additional circuitry is required for resonant removal. To the best of our knowledge, the proposed ESD tester is the first study to meet the JS-001 specification by applying a new switch instead of an existing mercury-wetted relay.     

A fast time-domain algorithm for the simulation of switching powerconverters

An efficient algorithm for the simulation of switched-mode power converters is developed. A Chebyshev series expansion is used to effectively solve the differential equations describing the system in each topology. The power of the new simulation technique lies both in the simple, but accurate, polynomial approximation for the state transition matrices and in the ability to explicitly obtain the instants at which the switching of the circuit topology takes place. The simulation technique is illustrated with reference to a simple Buck converter operating at a constant frequency. The derivation of the new algorithm is presented and its performance is analyzed. The case of a rapidly varying input forcing function is analyzed. Examples illustrating the generality and the computational efficiency of the algorithm are presented     

A frequency-dependent finite-difference time-domain formulation fortransient propagation in plasma

Previous FDTD (finite-difference time-domain) formulations were not capable of analyzing plasmas for two reasons. First, FDTD requires that at each time step the permittivity and conductivity be specified as constants that do not depend on frequency, while even for the simplest plasmas these parameters vary with frequency. Second, the permittivity of a plasma can be negative, which can cause terms in FDTD expressions to become singular. A novel FDTD formulation for frequency-dependent materials (FD)²TD has been developed. It is shown that (FD) ²TD can be applied to compute transient propagation in plasma when the plasma can be characterized by a complex frequency-dependent permittivity. While the computational example presented is for a pulse normally incident on an isotropic plasma slab, the (FD)²TD formulation is fully three-dimensional. It can accommodate arbitrary transient excitation, with the limitation that the excitation pulse must have no zero frequency energy component. Time-varying electron densities and/or collision frequencies could also be included. The formulation presented is for an isotropic plasma, but extension to anisotropic plasma should be fairly straightforward     

A new physical model for calculating storage time in GTO thyristors

A two-dimensional analytical model, developed from first principles, to substantiate the dependence of storage time on the nature of the gate current ramp, anode current, and device geometry, as observed in experimental studies on single-element gate turn-off thyristors (GTOs), is discussed. The model originates in the solution of the continuity equation in the p base for evaluation of the plasma squeezing rate. It addresses realistic issues, such as high injection effects, variation in the base transport factors, and the physical basis for the minimum ON region dimension, that are not considered in any previous treatment     

A simplified approach to time-domain modeling of avalanchephotodiodes

A simplified algorithm for calculating time response of avalanche photodiodes (APDs) is presented. The algorithm considers the time course of avalanche processes for the general case of position-dependent double-carrier multiplications including the dead space effect. The algorithm is based on a discrete time setting ideally suited for computer modeling and can be applied to any APD structure. It gives a fast and accurate estimation of the time and frequency response of APDs. As an example, the present method is applied to InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The variation of multiplication pain with bias voltage and 3-dB electrical bandwidth at different multiplication gain obtained using the new algorithm show good agreement with experimental results. The algorithm can be used to study temperature dependence of APD characteristics and can be easily extended to calculate the excess noise factor     

A fast maximum likelihood sequence decoding method for multicarrier DS-CDMA using frequency spread coding

This paper focuses on a multicarrier direct-sequence code-division multiple-access system using frequency spread coding, which was proposed by Matsutani and Nakagawa in 1999. Although this system is attractive due to its inherent frequency diversity gain without time or frequency redundancy, it is disadvantaged by its exponential complexity in the maximum likelihood sequence decoding (MLSD). To cope with such a bottleneck, this paper proposes a fast MLSD method which consists of a searching process along the eigenvectors of a symmetric matrix and a refining process. The fast MLSD method is compared with the normal MLSD method via theoretical analysis and simulation results.     

A simple method to evaluate the plasma spreading velocity in high power thyristors

The experimental determination of plasma spreading velocity versus current density in high power thyristors has been performed by many authors in different ways, especially by means of the observation of infrared recombination radiation [1], [2], [3] and the measurement of voltage with electrical probes [1], [4], [5]. In this paper a method is presented which, from the forward dynamic voltage measurement on finished devices, allows, on particular structures, to calculate analytically the experimental constants that appear in the relation between plasma velocity and current density.     

A scalar finite-difference time-domain approach to guided-wave optics

A finite-difference time-domain approach that solves the scalar wave equations is proposed and validated. The propagation, reflection, scattering, and radiation of electromagnetic waves in weakly guiding optical devices are described explicitly in the time domain. The method is applied to the simulation of guided-wave devices such as directional couplers and distributed feedback reflectors. A comparison to known analytical solutions shows good agreement.<>     

Electromagnetic wave effects on microwave transistors using afull-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies     

A time-domain physical optics heuristic approach to passiveintermodulation scattering

Passive intermodulation (PIM) is a phenomenon which often arises at junctions between different materials. This may be a major issue in tightly packed antenna farms as those typically present on communication satellites. Here, an heuristic nonlinear extension to the time-domain physical optics (TD-PO) is proposed, to take into account electromagnetic scattering at intermodulated frequencies when such a junction is illuminated by two impinging electromagnetic fields at different frequencies. Simulation results are compared with measures to validate the model     

A fast lightweight approach to origin-destination IP traffic estimation using partial measurements

In this paper, a novel approach is proposed for estimating traffic matrices. Our method, called PamTram for PArtial Measurement of TRAffic Matrices, couples lightweight origin-destination (OD) flow measurements along with a computationally lightweight algorithm for producing OD estimates. The first key aspect of our method is to actively select a small number of informative OD flows to measure in each estimation interval. To avoid the heavy computation of optimal selection, we use intuition from game theory to develop randomized selection rules, with the goals of reducing errors and adapting to traffic changes. We show that it is sufficient to measure only one flow per measurement period to drastically reduce errors-thus rendering our method lightweight in terms of measurement overhead. The second key aspect is an explanation and proof that an Iterative Proportional Fitting algorithm approximates traffic matrix estimates when the goal is a minimum mean-squared error; this makes our method lightweight in terms of computation overhead. A one-step error bound is provided for PamTram that bounds the average error for the worst scenario. We validate our method using data from Sprint's European Tier-1 IP backbone network and demonstrate its consistent improvement over previous methods.