Fast Transient Simulation Research Articles

Parallel-Distributed Block-LIM for Transient Simulation of Tightly Coupled Transmission Lines

In this paper, the parallel-distributed block-latency insertion method (block-LIM) is proposed for the fast transient analysis of a large-scale circuit that includes lots of coupling elements, such as mutual inductance and mutual capacitance. A conventional SPICE-like simulator requires an enormous cost for transient analysis of large-scale equivalent network that includes tightly coupled transmission lines, which is derived by using well-established commercially based extractors. The proposed method is based on the leapfrog algorithm, and can efficiently analyze tightly coupled transmission lines. First, the original LIM and the block-LIM are reviewed briefly. Next, the parallel-distributed block-LIM is proposed for the fast transient simulation and is implemented on the personal-computer-cluster system. Finally, some numerical results are shown, and it is confirmed that the proposed technique is useful and efficient for the simulations of the tightly coupled transmission lines.

A Precision and High-Speed Behavioral Simulation Method for Transient Response and Frequency Characteristics of Switching Converters

We propose a fast and precise transient response and frequency characteristics simulation method for switching converters. This method uses a behavioral simulation tool without using a SPICE-like analog simulator. The nonlinear operation of the circuit is considered, and the nonlinear function is realized by defining the nonlinear formula based on the circuit operation and by applying feedback. To assess the accuracy and simulation time of the proposed simulation method, we designed current-mode buck and boost converters and fabricated them using a 0.18-µm high-voltage CMOS process. The comparison in the transient response and frequency characteristics among SPICE, the proposed program on a behavioral simulation tool which we named NSTVR (New Simulation Tool for Voltage Regulators) and experiments of fabricated IC chips showed good agreement, while NSTVR was more than 22 times faster in transient response and 85 times faster in frequency characteristics than SPICE in CPU time in a boost converter simulation.

Transient Simulation of Complex High-Speed Channels via Waveform Relaxation

This paper presents a class of numerical schemes for fast transient simulation of electrically long and complex linear channels terminated by linear or nonlinear networks. The common denominator of all schemes is waveform relaxation. Domain decomposition approaches based on longitudinal and transverse partitioning are pursued, leading to various iterative methods characterized by different properties and numerical efficiency. For each scheme, we present a detailed convergence analysis and a set of numerical results obtained on industrial benchmarks. The main contribution of this paper is a novel theoretical framework based on a combination of longitudinal and transverse relaxation, leading to particularly efficient simulations when combined with compact channel representations based on delay-rational macromodels. Our prototypal implementation outperforms SPICE solvers, with speedup of up to two orders of magnitude.

Proposal of an alternative transmission line model for symmetrical and asymmetrical configurations

This article shows a transmission line model for simulation of fast and slow transients, applied to symmetrical or asymmetrical configurations. A transmission line model is developed based on lumped elements representation and state-space techniques. The proposed methodology represents a practical procedure to model three-phase transmission lines directly in time domain, without the explicit or implicit use of inverse transforms. In three-phase representation, analysis modal techniques are applied to decouple the phases in their respective propagation modes, using a correction procedure to set a real and constant matrix for untransposed lines with or without vertical symmetry plane. The proposed methodology takes into account the frequency-dependent parameters of the line and in order to include this effect in the state matrices, a fitting procedure is applied. To verify the accuracy of the proposed state-space model in frequency domain, a simple methodology is described based on line distributed parameters and transfer function associated with input/output signals of the lumped parameters representation. In addition, this article proposes the use of a fast and robust integration procedure to solve the state equations, enabling transient and steady-state simulations. The results obtained by the proposed methodology are compared with several established transmission line models in EMTP, taking into account an asymmetrical three-phase transmission line. The principal contribution of the proposed methodology is to handle a steady fundamental signal mixed with fast and slow transients, including impulsive and oscillatory behavior, by a practical procedure applied directly in time domain for symmetrical or asymmetrical representations.

Accurate and Efficient Computation of the Inductance Matrix of Transformer Windings for the Simulation of Very Fast Transients

When a transformer is subjected to very fast front transients, the penetration of the magnetic flux into the core becomes, in general, negligible. To represent this phenomenon, it is common practice to compute the winding inductance matrix (turn-to-turn) at very high frequencies using the expressions for air-core inductors. However, since the core becomes a magnetic insulating wall at very high frequencies (MHz), the distribution of the magnetic field is altered because the field cannot enter the region occupied by the core. Therefore, the air-core approximation formulae overestimate the inductance at high frequencies. This is especially true in the region inside the core window. Large errors are found when the inductances are computed with the air-core approximation. This paper presents a technique, based on the application of a multilayer method of images, to take the presence of the core into consideration. The final expressions are very simple, yet they give remarkably accurate results. Comparisons with finite-element analyses prove the excellent accuracy of the technique.

Block-Latency Insertion Method (Block-LIM) for Fast Transient Simulation of Tightly Coupled Transmission Lines

This paper describes a block-latency insertion method (LIM) for the fast transient simulation of the large networks with many coupling elements. First, the basic formulation of LIM is reviewed. Next, the block-LIM formulation for the network with many coupling elements, such as the mutual inductance, the mutual capacitance, and controlled sources is described. Then, the block-LIM algorithm is applied to the tightly coupled transmission lines, which are connected to each other by a number of mutual inductors and capacitors. Finally, some numerical results are shown, and it is confirmed that the proposed technique is useful and efficient for the simulation of the tightly coupled transmission lines.

A High-Frequency Circuit Model of a Potential Transformer for the Very Fast Transient Simulation in GIS

The high-frequency circuit model of potential and current transformers (PT/CTs) is indispensable in simulating the voltage stress in secondary circuits through the stray capacitances of the PT/CT particularly caused by the very fast transient overvoltages in gas-insulated subsystems. This paper presents a systematic methodology for establishing the high-frequency (0.1 to 11 MHz) circuit model of PTs based on the scattering parameters. First, the two-port <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> parameters of the PT are transformed into the Y parameters so that the equivalent ldquopirdquo circuit model can be established. Second, the vector-fitting code is used to approximate the admittances of the equivalent ldquopi rdquo circuit model by rational functions consisting of real as well as complex conjugate poles and residues. At last, a circuit synthesis method for the rational functions is applied to build the circuit model. The proposed method is general and robust. The simulation and measurement results are presented, confirming the validity of the proposed model.

Fast Transient Simulation of Power Distribution Networks Containing Dispersion Based on Parallel-Distributed Leapfrog Algorithm

This paper presents a fast transient simulation method for power distribution networks (PDNs) of the PCB/Package. Because these PDNs are modeled as large-scale linear circuits consisting of a large number of RLC elements, it takes large costs to solve by conventional circuit simulators, such as SPICE. Our simulation method is based on the leapfrog algorithm, and can solve RLC circuits of PDNs faster than SPICE. Actual PDNs have frequency-dependent dispersions such as the skin-effect of conductors and the dielectric loss. To model these dispersions, more number of RLC elements are required, and circuit structures of these dispersion models are hard to solve by using the leapfrog algorithm. This paper shows that the circuit structures of dispersion models can be converted to suitable structures for the leapfrog algorithm. Further, in order to reduce the simulation time, our proposed method exploits parallel computation techniques. Numerical results show that our proposed method using single processing element (PE) enables a speedup of 20--100 times and 10 times compared to HSPICE and INDUCTWISE with the same level of accuracy, respectively. In a large-scale example with frequency-dependent dispersions, our method achieves over 94% parallel efficiency with 5PEs.

IC thermal simulation and modeling via efficient multigrid-based approaches

The ever-increasing power consumption and packaging density of integrated systems creates on-chip temperatures and gradients that can have a substantial impact on performance and reliability. While it is conceptually understood that a thermal equivalent circuit can be constructed to characterize the temperature gradients across the chip, direct and iterative solutions of the corresponding three-dimensional (3-D) equations are often intractable for a full-chip analysis. Integrated circuit (IC)-specific multigrid (MG) techniques for fast chip level thermal steady-state and transient simulation are proposed. This approach avoids an explicit construction of the matrix problem that is intractable for most full-chip problems. Specific MG treatments are proposed to cope with the strong anisotropy of the full-chip thermal problem that is created by the vast difference in material thermal properties and chip geometries. Importantly, this paper demonstrates that only with careful thermal modeling assumptions and appropriate choices for grid hierarchy, MG operators, and smoothing steps across grid points can a full-chip thermal problem be accurately and efficiently analyzed. This paper further speeds up the large thermal transient simulations by incorporating reduced-order thermal models that can be efficiently extracted under the same MG framework. The experiments carried out in this work have shown that the proposed methodology provides sufficient efficiency in both runtime and memory usage.

Fast Transients Analysis of Nonuniform Multiconductor Frequency-Dependent Transmission Lines

In this work, a new model for the simulation of fast transients on nonuniform multiconductor transmission lines is presented. The proposed model is based on the method of characteristics of partial differential equations theory and includes a variation of the electrical parameters with the distance and frequency. In addition, Norton circuits for the transmission line ends, which allow the inclusion of the model into general-purpose programs, are presented. Results obtained with the proposed model are compared with those obtained with the Electromagnetic Transients Program and the Numerical Laplace Transform method.

Impact of Self-Heating Effect on Long-Term Reliability and Performance Degradation in CMOS Circuits

As the technology feature size is reduced, the thermal management of high-performance very large scale integrations (VLSIs) becomes an important design issue. The self-heating effect and nonuniform power distribution in VLSIs lead to performance and long-term reliability degradation. In this paper, we analyze the self-heating effect in high-performance sub-0.18-/spl mu/m bulk and silicon-on-insulator (SOI) CMOS circuits using fast transient quasi-dc thermal simulations. The impact of the self-heating effect and technology scaling on the metallization lifetime and the gate oxide time-to-breakdown (TBD) reduction are also investigated. Based on simulation results, an optimized clock-driver design is proposed. The proposed layout reduces the hot-spot temperature by 15/spl deg/C and by 7/spl deg/C in 0.09-/spl mu/m SOI and bulk CMOS technologies, respectively.

Statistical simulation of gate dielectric wearout, leakage, and breakdown

We present a set of models for the simulation of gate dielectric leakage, wearout, and breakdown. The leakage model accounts for direct and trap-assisted tunneling through the dielectric layer. Wearout is caused by the leakage-induced creation of neutral defects at random positions in the dielectric layer, which, if occupied, degrade the threshold voltage of the device. Gate dielectric breakdown is triggered by the formation of a conductive path through the insulator. To allow trap characterization and for the simulation of fast transients the modeling of trap charging and decharging processes is outlined. The models have been implemented into a three-dimensional device simulator and are used for the characterization of ZrO 2 -based dielectrics and for the study of gate leakage and wearout effects in standard CMOS inverter circuits.

A note on the thermal modelling of power semiconductor devices using the network analogue

AbstractThe aim of this note is to point out that the boundary condition for the network modelling of thermal problems may have been incorrectly used in some previous studies. It is shown that the accuracy of the network analogue or the equivalent finite‐difference method is on the par with the finite‐element method for very fast transient thermal simulations. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Fast transients analysis of nonuniform transmission lines through the method of characteristics

A new method for the simulation of fast transients on nonuniform transmission lines is proposed in this paper. The method is based on the method of characteristics of partial differential equations theory. It is shown that the proposed method can easily include resistive losses and wave speed variations. In addition, in order to bring the proposed method to practical usefulness, a Norton equivalent for transmission line ends is presented. At any given time, the Norton equivalent of each transmission line end is independent of the line's interior behavior at that time, therefore the model can readily be included into any electrical network transients simulation program. The advantages of the method are shown here by applying them to two problems. The first one consists of analyzing the effects of nonuniformities caused by the sagging of conductors on an aerial line. For this case, results from electromagnetic transients program and finite differences time domain simulations are included for comparison purposes. The second application consists of the simulation of a fast impulse propagating along a transmission tower modeled as a network of vertical and horizontal transmission lines.

Wavelet-based high-order adaptive modeling of lossy interconnects

This paper presents a numerical-modeling strategy for simulation of fast transients in lossy electrical interconnects. The proposed algorithm makes use of wavelet representations of voltages and currents along the structure, with the aim of reducing the computational complexity of standard time-domain solvers. A special weak procedure for the implementation of possibly dynamic and nonlinear boundary conditions allows one to preserve stability as well as a high approximation order, thus leading to very accurate schemes. On the other hand, the wavelet expansion allows the computation of the solution by using few significant coefficients which are automatically determined at each time step. A dynamically refinable mesh is then used to perform a sparse time-stepping. Several numerical results illustrate the high efficiency of the proposed algorithm, which has been tuned and optimized for best performance in fast digital applications typically found on modern PCB structures.

Latency insertion method (LIM) for the fast transient simulation of large networks

In this work, a finite difference formulation is used to simulate large networks. The method makes use or introduces reactive latency in all branches and nodes of a circuit to generate update algorithms for the voltage and current quantities. A criterion is established that guarantees the stability of the algorithm for specified choices of the time step. Because of its linear numerical complexity, several orders of magnitude in speedup over matrix-based methods are obtained. Nonlinear networks can also be simulated by the formulation. Several comparisons are made with standard simulators in order to evaluate the accuracy and efficiency of the algorithm. In all cases that satisfy the stability criterion, good agreements with established techniques are obtained.

Fast transient simulation of eddy current interconnection effects using reduced order models

A method for the efficient simulation of the time domain response of transmission lines including skin effect is developed. The finite element method (FEM) is employed together with Silvester's modal analysis procedure to model eddy currents in arbitrary geometries. For transient simulation, asymptotic waveform evaluation (AWE) provides a general, efficient and accurate way to determine the transient responses of large linear circuits in terms of the dominant poles and residues. Once the poles and residues are obtained, transient simulation is performed by using recursive-convolution. An application example is provided to demonstrate the effectiveness of the proposed approach.

Fast transient simulation of Markovian models of highly dependable systems

In this paper we investigate fast simulation techniques for the estimation of transient measures in Markovian models of highly dependable systems. For such models, standard simulation techniques are inefficient as system failure events are rare. Two importance sampling techniques, namely forcing and failure biasing, have been found to increase the efficiency in estimating such measures. However, experiments have shown that these techniques work well only for the case where the time horizon is ‘small’ and result in poor estimates otherwise. To gain a better understanding of this phenomenon we analyze the importance sampling heuristics for the case of estimating the expected interval unavailability. We show that for any fixed given time horizon the estimates using importance sampling have bounded relative error (i.e., the relative error of the simulation estimate remains bounded as failure rates tend to zero; this is contrasted to standard simulation in which the relative error tends to infinity). However, for time horizons that are large these techniques are shown to be inefficient. For this case we develop bounds on the measure and then instead of estimating the measure we estimate these bounds. We prove that these bounds can be very efficiently estimated and that for time horizons that are not ‘small’, the bounds approach the measure as failure rates tend to zero.

Simulation of fast transients in fluid transport equipments and utility networks

A model allowing dynamic simulation of processes involving compression, expansion, heat generation and transfer in fluids is presented. Equations are developed for some equipment models, based on one-dimensional flow approximation. The architecture of a simulation package based on the object paradigm is described. The programme has been validated with experimental data : surge onset in compression systems has been satisfactorily predicted.

Higher‐order modelling of the diffusion dynamics in a bipolar transistor

AbstractA higher‐order diffusion model for a bipolar transistor has been developed. This model is based on the Padé approximation of the quasi‐static expansions of the base and collector currents and gives improved accuracy for the simulation of fast transients and periodic operation at high frequencies. the effect of higher‐order circuit elements on accuracy is demonstrated by calculating the transient response to a step excitation and by determining the scattering parameters of a transistor model with higher‐order elements linearized about an operating point. the higher‐order model is replaced by an equivalent circuit including only conventional elements, and the transient behaviour of these two models is compared.