State-variable-based transient circuit simulation using wavelets

For the first time a state variable transient analysis using wavelets is developed and implemented in a circuit simulator. The formulation is particularly well suited to modeling RF and microwave circuits and is validated by considering a nonlinear transmission line. However, results indicate that still more research is needed to make this method efficient for the simulation of large circuits     

New efficient LS and SVD based techniques for high-resolutionfrequency estimation

New least squares and singular value decomposition based methods for the estimation of the frequencies of complex sinusoids in white noise are presented. The methods are based on a new symmetric prediction problem that has some very useful properties leading to algorithms that have considerably reduced complexity. The new symmetric predictor is superior in performance as compared to the well known symmetric Smoother and has a performance comparable to other well known methods. Finally a new LS based method, which combines the new prediction technique with the FBLP method is proposed. This method performs slightly better than the FBLP offering at the same time a significant computational saving. As a by-product in the derivation of the new methods is the establishment of some useful properties concerning the eigenstructure of Hermitian and Persymmetric matrices     

Identification of transient renal autoregulatory mechanisms using time-frequency spectral techniques

Identification of the two principal mediators of renal autoregulation from time-series data is difficult, as both the tubuloglomerular feedback (TGF) and myogenic (MYO) mechanisms interact and share a common effector, the afferent arteriole. Moreover, although both mechanisms can exhibit oscillations in well-characterized frequency bands, these systems often operate in nonoscillatory states not detectable by frequency-domain analysis. To overcome these difficulties, we have developed a new approach to the characterization of the TGF and MYO systems. A laser Doppler probe is used to measure fluctuations in local cortical blood flow (CBF) in response to spontaneous changes in blood pressure (BP) and to large imposed perturbations in BP, which elicit strong, simultaneous, transient, oscillatory blood flow responses. These transient responses are identified by high-resolution time-frequency spectral analysis of the time-series data. In this report, we compare four different time-frequency spectral techniques (the short-time Fourier transform (STFT), smoothed pseudo Wigner-Ville, and two recently developed methods: the Hilbert-Huang transform and time varying optimal parameter search (TVOPS)) to determine which of these four methods is best suited for the identification of transient oscillations in renal autoregulatory mechanisms. We found that TVOPS consistently provided the best performance in both simulation examples and identification of the two autoregulatory mechanisms in actual data. While the STFT suffers in time and frequency resolution as compared to the other three methods, it was able to identify the two autoregulatory mechanisms. Taken together, our experience suggests a two level approach to the analysis of renal blood flow (RBF) data: STFT to obtain a low-resolution time-frequency spectrogram, followed by the use of a higher resolution technique, such as the TVOPS, if even higher time-frequency resolution of the transient responses is required.     

Trap spectroscopy of a-Si:H diodes using transient current techniques

Transient current techniques have been applied to hydrogenated amorphous silicon (a-Si:H) solar cells to obtain information about the electron traps in the upper half of the band gap. These studies lead to the conclusion that electron trapping occurs in specific regions distributed throughout the a-Si:H. A model based on these trapping regions becoming negatively charged as electrons are captured and thus opposing further capture is presented. Because of this inhomogeneous capture only the lower limit to the density of traps is obtained.     

A state-space formulation of transient electromagnetic scattering

For a perfectly conducting scatterer, a state-space formulation for the transient scattered field is given for single-input and multiple-output. The formulation is based on the meromorphic property of the scattered field and includes the constraint that the natural body resonances are invariant with observation point.     

Design of high-speed simulation models for mobile fading channelsby using table look-up techniques

This paper describes a procedure for the design of fast simulation models for Rayleigh fading channels. The presented method is based on an efficient implementation of Rice's sum of sinusoids by using table look-up techniques. The proposed channel simulator is composed of a few numbers of adders, storage elements, and simple modulo operators, whereas time-consuming operations like multiplications and trigonometric operations are not required. Such a multiplier-free simulation model is introduced as a high-speed channel simulator. It is shown that the high-speed channel simulator can be interpreted as a finite state machine which generates deterministic output envelope sequences with approximately Rayleigh distribution. The statistical properties of the designed high-speed channel simulator are investigated analytically and compared with the statistics of the underlying Rayleigh reference model. Results of experiments for measuring the speed of the presented and other types of channel simulators are also presented     

Performance analysis of digital lightwave systems using efficientcomputer simulation techniques

Analytically-based methods for evaluating the performance of digital lightwave systems in terms of bit error rates (BERs) are extremely difficult to develop without making restrictive assumptions. A Monte Carlo simulation approach can offer an attractive alternative. However, for typical optical systems, this approach would require an excessive amount of computer time. Importance sampling (IS) is a variance reduction method which can substantially increase the computational efficiency of Monte Carlo simulations. This paper presents an IS method to efficiently evaluate the BERs of direct-detection optical systems employing avalanche photodiode (APD) receivers. Specifically, using a heuristic argument based on large deviations theory, a large class ℱ of exponentially twisted sampling distributions for the APD-based receiver is developed. It is then demonstrated that when used as a sampling distribution, the “optimized” exponentially twisted distribution of large deviations theory is the most efficient distribution among the sampling distributions in ℱ. Further, it is demonstrated that such a distribution would estimate the performance of optical systems with a high degree of accuracy to warrant its possible use as a powerful and flexible tool in computer-aided design, analysis and modeling of fiber-optic transmission systems     

Parallel simulation techniques for large-scale networks

Simulation has always been an indispensable tool in the design and analysis of telecommunication networks. Due to performance limitations of the majority of simulators, usually network simulations have been done for rather small network models and for short timescales. In contrast, many difficult design problems facing today's network engineers concern the behavior of very large hierarchical multihop networks carrying millions of multiprotocol flows over long timescales. Examples include scalability and stability of routing protocols, packet losses in core routers, of long-lasting transient behavior due to observed self-similarity of traffic patterns. Simulation of such systems would greatly benefit from application of parallel computing technologies, especially now that multiprocessor workstations and servers have become commonly available. However, parallel simulation has not yet been widely embraced by the telecommunications community due to a number of difficulties. Based on our accumulated experience in parallel network simulation projects, we believe that parallel simulation technology has matured to the point that it is ready to be used in industrial practice of network simulation. This article highlights work in parallel simulations of networks and their promise     

Large scale P/G grid transient simulation using hierarchical relaxed approach

This paper proposes a hierarchical relaxed approach to analyze large scale on-chip power/ground (P/G) grids with C4 packages efficiently. Different from the existing hierarchical approach where macro models and time-consuming matrix density reduction technique are used, this novel approach uses an iterative relaxation procedure to explicitly exploit the character of boundary nodes caused by C4 bumps, which can lead to more speedup without losing any accuracy. Also, an efficient partition strategy is generated to help the new algorithm to achieve higher performance on C4 based P/G grid. Experimental results demonstrate that the new algorithm is as accurate as the existing hierarchical method while it delivers more speedup over it for C4 based P/G grid.     

A novel dispersive FDTD formulation for modeling transient propagation in chiral metamaterials

Chiral media engineered for applications at microwave frequencies can be described as metamaterials composed of randomly oriented helices (with sizes typically less than a wavelength) embedded within an achiral background that is characterized by its permittivity and permeability. Chiral metamaterials embody properties of magnetoelectric coupling and polarization rotation. Chiral media are also highly dispersive and no effective full-wave time domain formulation has been available to simulate transient propagation through such an important class of metamaterials. A new finite-difference time-domain (FDTD) technique is introduced in this paper to model the interaction of an electromagnetic wave with isotropic dispersive chiral metamaterials, based on the implementation of a wavefield decomposition technique in conjunction with the piecewise-linear recursive convolution method. This formulation represents the first of its kind in the FDTD community. The FDTD model is validated by considering a one-dimensional example and comparing the simulations with available analytical results. Moreover, the FDTD technique is also used to investigate the propagation of electromagnetic waves through multilayered metamaterial slabs that include dispersive chiral and double-negative media. Hence, this model enables the investigation of complex dispersive metamaterials with magnetoelectric coupling and double-negative behavior as well as facilitates the exploitation of their unique properties for a variety of possible applications.     

74LS161异步置零法构成任意进制计数器的Multisim仿真

介绍了集成4位二进制计数器74LS161异步置零法构成任意进制计数器的Multisim仿真方案,即以波形方式显示计数器的计数过程、过渡状态形成异步置零信号的过程,用四踪示波器以面板部分重叠显示方法同步显示时钟脉冲信号、异步置零信号及状态输出信号。分析了过渡态及异步置零信号的延时方法,指出了Multisim中74LS161计数器时钟触发方式的错误及修正方法。所述方法的创新点是解决了计数器的工作波形无法用电子实验仪器进行分析验证的问题。     

Efficient techniques for the simulation of computer communicationsnetworks

The statistical nature of Monte Carlo techniques presents significant computational problems in the simulation of computer communications networks. A variety of techniques has been developed over the years to improve the computational efficiency of simulation models of general queuing networks, some of which have been applied to communication networks. The authors review the status of efficiency-enhancing techniques as they relate to the simulation of computer communications networks, present some novel approaches, and suggest promising areas for future research     

激光成像雷达成像仿真技术研究

提出了一种模拟激光成像雷达图像的新方法,该方法基于激光成像雷达的基本工作原理,结合激光在大气传输过程中的消光效应和激光成像雷达的光电噪声,对整个成像过程进行了高精度模拟.实验结果表明,该方法仿真的激光回波波形与实测波形比较接近,仿真得到的图像具有较高的可信度,并且已经在激光成像雷达样机设计和后继的匹配定位导航研究中得到应用.     

Application of recursive convolution to transient simulation of interconnects using a hybrid phase-pole macromodel

A hybrid phase-pole macromodel (HPPM), which explicitly includes phase shifts (time delays) in addition to the system poles, was recently developed for modeling interconnects. In this paper, the HPPM is applied to the transient simulation of interconnects. First, the time-domain source waveform is expanded in terms of triangular expansion functions. Knowledge of the triangle impulse response (TIR) for an interconnect, which is represented in the form of an HPPM, then allows for the time domain simulation of the interconnect. A recursive convolution algorithm is adopted to carry out the required convolutions efficiently in the transient simulator. Combining this transient simulator with an HPPM extractor yields a transient interconnect signal analysis tool.     

Chebyshev series integration method for transient simulation ofswitched networks

An efficient integration routine based on the Chebyshev series expansion is given. Adoption of a Chebyshev expansion minimizes the order of the polynomial approximation which together with a number of basic properties of the expansion results in an efficient integration method. Furthermore, integration error control may conveniently be approached by monitoring the coefficients of the expansion. The proposed error control scheme varies the expansion order while keeping the step size fixed. A software program for the simulation of networks with ideal switches was written which incorporates the above features. Two examples, one of a nonswitched network and the other of a switched network, are given to illustrate the speed and accuracy of the program and effectiveness of the error control scheme. To quantify the advantages of the proposed scheme, a comparison is made with a previously developed simulator (viz., LAPS) and also a commercially available SPICE program     

Negative-gate to substrate erase transient simulation for flash memory

We present a detailed and accurate physics based transient simulation for modeling flash memory erasing. Typical cells are erased by moving electrons from the floating gate to the drain, source or substrate. This paper addresses substrate erasing using a negative gate bias voltage based on the approximate solution to Poisson’s equation. Substrate erasing using a negative gate bias voltage is one of the more prevalent ways to erase flash memory in currently available consumer products. Many papers have been published on this topic but rarely present detailed derivations and none using this exact set of equations to model this erasing process.     

Direct time-domain techniques for transient radiation and scattering from wires

This is a tutorial introduction to transient electromagnetics, focusing on direct time-domain techniques. We examine physical, mathematical, numerical and experimental aspects of time-domain methods, with emphasis on wire objects excited as antennas or scatterers. Numerous computed examples illustrate the characteristics of direct time-domain procedures, especially where they may offer advantages over the more familiar frequency-domain techniques. These advantages include greater solution efficiency for many types of problems, the ability to handle nonlinearities, improved physical insight and interpretability, availability of wide-band information from a single calculation, and the possibility of isolating interactions among various parts of an object using time-range gating.     

Complete transient simulation of flash EEPROM devices

A two-dimensional device simulator which allows the complete transient simulation of nonvolatile memories is presented. The simulator has been derived from HFIELDS and incorporates models to account for Fowler-Nordheim tunneling, hot electron injection through silicon dioxide, and band-to-band tunneling in silicon. The physical models have been verified by comparing simulations with measurements performed on suitable test structures where good agreement has been obtained. The tool has been used to investigate flash EEPROM device scaling and to evaluate a published scaling scenario     

Concise transient SPICE model for bipolar power transistor quasi-saturation simulation

A concise transient SPICE model is presented in this paper to predict both the static and the switching behaviour of power transistors, with emphasis placed on quasi-saturation effects. The model is proposed to simulate both ohmic and non-ohmic quasi-saturation phenomena by automatically adjusting the hole injection ratio term. The model incorporates the currently used Gummel-Poon (GP) model and an additional charge-control relation for the transistor's epitaxial collector. The turn-off charge removal phenomenon is not modelled specifically; however, the charge-control equation for the epitaxial collector region may partly simulate this effect where the quasi-saturation region is entered. The validity of the model is verified by comparison between the original SPICE bipolar junction transistor model and experimental data for both DC and turn-on conditions. Methods for determining the model parameters are described.