Time-domain Circuit Simulation Research Articles

A new pre-conditioned STDP rule and its hardware implementation in neuromorphic crossbar array

This paper proposes a new pre-conditioned spike-timing-dependent plasticity (STDP) learning rule as well as an efficient system-level time-domain circuit modeling and simulation method for the whole crossbar array structure. First, the new pre-conditioned STDP rule is conceived by exercising a slight perturbation to the conventional STDP curve. Software-wise, it can be described in spiking neural network (SNN) codes, while hardware-wise, it is realized by the memristor crossbar array in conjunction with specific spike signals, just as the conventional STDP. The new STDP rule enables the neural network in a neuromorphic chip to achieve better performance both in terms of software and hardware implementation compared with the conventional STDP rule. Second, a time-domain circuit modeling method is proposed for the simulation of the whole crossbar array. Numerical experiments demonstrate that the new pre-conditioned STDP is superior to the conventional STDP both in terms of accuracy and low power consumption. At the software level, a 784 × 100 spiking neural network, trained by the pre-conditioned STDP, for the MNIST handwritten digit recognition achieves an accuracy of 85.90%, which is 3.09% higher than that trained by the conventional STDP. At the hardware level, a downscaled 196 × 10 crossbar array is simulated and trained. The crossbar array trained by the new STDP consumes 21.5% less power than that trained by the conventional STDP. Moreover, it does not compromise the original robustness when subject to non-ideal characteristics such as variation of conductance and resistance of the interconnect in the crossbar array.

Prediction of EMI Filter Attenuation in Power-Electronic Converters via Circuit Simulation

This article investigates the conducted-emission (CE) suppression characteristics of electromagnetic interference (EMI) filters used in power-electronic equipment by time-domain circuit simulation. An operational definition of insertion attenuation is introduced by comparing the CE in the absence and in the presence of the EMI filter. For the sake of exemplification, the analysis focuses on switched-mode dc–dc converters. It is shown that the EMI-filter attenuation behaves differently from the standard insertion loss (IL) and exhibits peculiar properties in these circuits. Namely, its response is known at discrete frequencies where the converter generates CE and may strongly depend on the harmonic index so to jump between quite different levels from a harmonic component to the next one, with a pseudoperiodic behavior, which can be related to the duty cycle. This effect is caused by circuit nonlinearity and is partially mitigated if the simulation accounts for two practically relevant aspects: random instability of the duty cycle and resolution bandwidth of the EMI receiver. The dependence of the common-mode (CM) and differential-mode attenuations on the loading conditions and duty cycle is analyzed, and it is shown that linear IL models provide reasonable predictions of CM attenuation only. Finally, experimental evidence of the unveiled phenomena is presented.

Fast and Stable Time-Domain Simulation Based on Modified Numerical Inversion of the Laplace Transform

This article presents a new algorithm for time-domain circuit simulation based on numerical inversion of Laplace transform (NILT). The proposed method, labeled NILT n, shows that for the same computational cost of the conventional NILT, referred to as NILT0, the approximation error is reduced by a significant factor, permitting time-marching with much larger time steps and, consequently, saving significant computational cost per time step. Numerical experiments are presented to demonstrate the efficiency and accuracy of the proposed approach.

InSb pixel loaded microwave resonator for high-speed mid-wave infrared detection

High-speed mid-wave infrared (MWIR) detectors are of significant interest for a wide range of applications in communication and spectroscopy. High-speed photodetection is conventionally achieved using reverse biased semiconductor p-i-n junction devices. However, implementing such structures in the mid-infrared (mid-IR) is challenging due to both the limited available material platforms and challenges associated with device design. Here we demonstrate a high-speed MWIR detector architecture that uses a microwave resonator circuit loaded with a photoconductive indium antimonide (InSb) pixel, originally grown highly lattice-mismatched on a GaAs substrate. Time domain measurements demonstrate sub-nanosecond detector response at temperatures from 77 K to room temperature. Frequency response measurements demonstrate that optical signals modulated at frequencies as high as 2 GHz can be well resolved up to room temperature. Time domain circuit simulations support the experimentally measured short minority carrier lifetimes in the InSb pixel, while also suggesting a circuit time constant of ~200 ps, which is ultimately the limiting factor for the bandwidth of the presented detector architecture. Our results provide an alternative approach for the development of contact-free, high-speed infrared detectors capable of directly interfacing with microwave components and structures for a range of RF/mid-IR applications.

System level design of wireless sensor node powered by piezoelectric vibration energy harvesting

This paper proposes a design of wireless sensor node powered by piezoelectric vibration energy harvesting system. A complete system level coupling circuit model is established to predict the performance characteristics. The piezoelectric vibration energy harvester (PVEH) is based on a PZT bimorph cantilever, in which a big proof mass is introduced to decrease resonant frequency and a shell served as a stopper to avoid overload. Lumped parameters of the model are identified by experiments and calculations. Electromechanical analogy model of PVEH is simulated in LTspice software. The power consumption of a temperature WSN is tested and the equivalent load model is simulated. A power management circuit (PMC) with LTC3588-1 is designed for rectifying and regulating output of PVEH. Electrical energy is stored in a capacitor. Finally, a system level coupling model is established. Time domain circuit simulation can provide the detailed parameters about the WSN powered by PVEH such as full charge time and sustainable time of the system. Test curves of capacitor charging and WSN power supply in prototype testification show good consistency with the simulation results in LTspice. An application for temperature WSN powered by PVEH is testified as an example. The method and model proposed in this paper can set up a reference to optimize system parameters for WSN powered by PVEH.

HTS Transformer–Rectifier Flux Pump Optimization

Flux pumps are a type of wireless superconducting power supply which can provide advantages over traditional superconducting systems. This work reports on time-domain circuit simulations in LTspice of a transformer-rectifier flux pump. The simulations are compared with an experimental system employing ac-field switches and show good agreement. Further simulations show that a key component for the advance of transformer-rectifier flux pumps is the development of improved superconducting switches. Work to date by the authors towards developing high temperature superconducting (HTS) switches with high off-state resistance, fast recovery time and high critical current is reported on. Future work is detailed, and it is concluded that if improved HTS switches are developed, flux pumps will be a competitive technology and may start to replace conventional superconducting power supplies.

Electromagnetic transient analysing of neutral bus in UHVDC converter station

Transient processes at neutral bus of ultra-high value direct current (UHVDC) converter station received insufficient attention, because of the lower amplitude compare to poles. However due to the lower insulation level, electromagnetic transient processes at neutral bus may cause serious fault, and become an important issue that should be studied carefully in the design stage. A method to analyse the electromagnetic transient based on time-domain wide-band circuit simulation is proposed in this study. Models of major equipment are described. The electromagnetic transient of a ±800 kV converter station is calculated. The transient under different operation statuses is compared. Effects of suppression method such as arresters and capacitors are analysed.

Eye Height/Width Prediction From <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math> </inline-formula>-Parameters Using Learning-Based Models

Design space exploration and sensitivity analysis for electrical performance of high-speed serial links is a critical and challenging task for a robust, cost-efficient, and signal-integrity-compliant channel design. The generation of time-domain (TD) metrics like eye height and eye width at higher bit error rates requires longer bit sequences in TD circuit simulation, which is compute time intensive. Intelligent techniques to identify smaller design sets that cover the design space optimally may provide incorrect sensitivity analysis. This paper explores learning-based modeling techniques that rapidly map relevant frequency-domain metrics like differential insertion loss and total cross talk, in the presence of equalization, to TD metrics like eye height and eye width, thus facilitating a full-factorial design space sweep. Numerical results performed with multilayer-perceptron-based artificial neural network as well as least-squares support vector machine (LS-SVM) on Serial ATA 3.0 and Peripheral Component Interconnect Express Gen3 channels generate an average error of less than 2%.

Circuit realization method for reduced order inductive PEEC modeling circuits

Purpose To synthesize equivalent circuit obtained from reduced order model of large scale inductive PEEC circuits. Design/methodology/approach This paper describes an original approach for reducing and synthesizing large parasitic RLM electrical circuits coming from inductive Partial Element Equivalent Circuit (PEEC) models. The proposed technique enables the re-use of the reduced order model in the time domain circuit simulation context. Findings The paper shows how to use a synthesis method to realize an equivalent circuit issued from compressed PEEC circuits. Originality/value The coupling between methods PEEC and a compressed method as Fast Multipole Method (FMM) in order to reduce time and space consuming are well-known. The innovation here is to realise a smaller circuit equivalent with the original large scale PEEC circuits to use in temporal simulation tools. Moreover, this synthesis method reduces time and memories for modelling industrial application while maintaining high accuracy.

An integrated 3G/Bluetooth and UWB antenna with a band-notched feature

In this article, the design and analysis of a compact slot antenna that covers 3G, Bluetooth, and the UWB bands with the standard band-notched function at 3.6 GHz are presented and investigated. A rectangular wide-slot etched off the ground plane is used to control the low operating frequency band and the impedance matching of the proposed antenna. A manipulated rectangular tuning stub is used to enhance and control the operating bandwidth at the high frequency band. The proposed antenna is fabricated and is successfully simulated and measured. The results indicate that the proposed antenna yields an impedance bandwidth of about 7.75 GHz (from 1.9 to 9.65 GHz) defined by VSWR ≤ 2 for UMTS (1.920–2.170 GHz)/Bluetooth (2.4–2.484 GHz)/3GPP (2.57–2.62 GHz), and UWB (3.1–9.65 GHz) applications with good radiation characteristics. To reduce interference between the UWB system and the WiMAX system (3.3–3.9 GHz), a U-shaped slot is employed in the microstrip feeding line to create notched band of 3.2–4.0 GHz. Furthermore, a mathematical circuit model compatible with time-domain circuit simulators, which is based on a vector fitting technique, is also illustrated to investigate the proposed antenna characteristics.

Stochastic Testing Method for Transistor-Level Uncertainty Quantification Based on Generalized Polynomial Chaos

Uncertainties have become a major concern in integrated circuit design. In order to avoid the huge number of repeated simulations in conventional Monte Carlo flows, this paper presents an intrusive spectral simulator for statistical circuit analysis. Our simulator employs the recently developed generalized polynomial chaos expansion to perform uncertainty quantification of nonlinear transistor circuits with both Gaussian and non-Gaussian random parameters. We modify the nonintrusive stochastic collocation (SC) method and develop an intrusive variant called stochastic testing (ST) method to accelerate the numerical simulation. Compared with the stochastic Galerkin (SG) method, the resulting coupled deterministic equations from our proposed ST method can be solved in a decoupled manner at each time point. At the same time, ST uses fewer samples and allows more flexible time step size controls than directly using a nonintrusive SC solver. These two properties make ST more efficient than SG and than existing SC methods, and more suitable for time-domain circuit simulation. Simulation results of several digital, analog and RF circuits are reported. Since our algorithm is based on generic mathematical models, the proposed ST algorithm can be applied to many other engineering problems.

Operating Strategies of Switched Reluctance Machines for Exhaust Gas Energy Recovery Systems

This paper presents an operating strategy for high-speed switched reluctance (SR) generators employed in exhaust gas energy recovery systems. The machine is operated in “single pulse” mode, and a parametric study of the control angles is performed to analyze the machine operation. It is shown that, for given speed and power, optimum sets of control angles exist, which achieve maximum machine efficiency and minimum thermal stress. This study is undertaken using a coupled nonlinear modeling approach, combining magnetostatic finite-element analysis with time-domain circuit simulation. The results are compared with measurements performed on an SR generator designed for a prototype exhaust gas energy recovery system, showing overall good agreement.

Successful Practices for the Modeling of Printed Circuit Boards and Substrates Using Electromagnetic Field Solvers

The aim of this work is to provide strategies for creating highly accurate models of printed circuit boards (PCBs) and substrates using electromagnetic field solvers. It will examine how to choose the correct field solver for a particular application from among full-wave, modal decomposition, finite element and boundary element methods. Tradeoffs between time and accuracy of the different solvers will be discussed. The focus is on model creation for use in time domain circuit simulators, but analysis of the frequency domain data will be used to correlate measurement to simulation. The problem of correlating simulation results with measurements is also discussed. A physical layer reference design (PLRD) board has been constructed, measured and simulated with the various field solvers. The results are analyzed to understand why differences occur between simulation and measured data. The impacts of these differences on system-level simulations of high-speed serial links are studied using a circuit simulator.

Study on Frequency Dependency of ON-Resistance and Pulse-Loss Calculation of MOSFETs for Switch Mode Power Supply

Global efforts toward energy conservation, increasing data centers, and the increasing use of IT equipments are leading to a demand in reduced power consumption of equipments, and power efficiency improvement of power supply units is becoming a necessity. MOSFETs are widely used for their low ON-resistances. Power efficiency is designed using time-domain circuit simulators, except for transformer copper-loss, which has frequency dependency which is calculated separately using methods based on skin and proximity effects. As semiconductor technology reduces the ON-resistance of MOSFETs, frequency dependency due to the skin effect or proximity effect is anticipated.In this study, ON-resistance of MOSFETs are measured and frequency dependency is confirmed. Power loss against rectangular current pulse is calculated. The calculation method for transformer copper-loss is expanded to MOSFETs. A frequency function for the resistance model is newly developed and parametric calculation is enabled. Acceleration of calculation is enabled by eliminating summation terms. Using this method, it is shown that the frequency dependent component of the measured MOSFETs increases the dissipation from 11% to 32% at a switching frequency of 100kHz.From above, this paper points out the importance of the frequency dependency of MOSFETs' ON-resistance, provides means of calculating its pulse losses, and improves loss calculation accuracy of SMPSs.

Interconnect Analysis for 80-Gbps Serial Link Design

This paper presents a case study of the modeling and simulation methods used to design the signal path for a proposed 80-Gbps serial data link between digital systems. This design includes flip-chip transitions from custom IBM 8HP integrated circuits to multilayer organic substrates, with coaxial-cable connections between substrates. Discussion topics include interconnect material selection, detailed 3-D electromagnetic modeling of the conductor transitions and signal paths, time-domain circuit simulation of the complete data path including the driver and receiver, and bit-error rate analysis of the complete link. Simulated data are presented.

Guest editorial

Recent advances in wireless and microwave communication systems (higher operation frequency bands, more compact topologies containing MMICs and MEMS, wideband automotive, space and biomedical modules) have increased the necessity of fast and accurate numerical simulation techniques. Unlike hybrid microwave integrated circuits at low frequencies, it is extremely difficult and essentially impossible to adjust the circuit and radiation characteristics of communication modules once they are fabricated. For this reason, many practical geometries, especially in microwave and millimeter-wave integrated circuits (MMIC), packaging, interconnects, sub-nanosecond digital electronic circuits [such as multi-chip modules (MCM)], and antennas used in wireless and microwave communication systems, have been left relatively untreated due to their complexity and the inability of the existing techniques to deal with requirements for large size and high resolution. The starting point for the development of efficient numerical algorithms is an accurate characterization of the passive and active structures involved in the topologies. Although most commercial CAD programs are based on curve-fitting formulas and lookup tables and not on accurate numerical characterization, the latter can be used if it is fast enough. In addition, it can be used to generate lookup tables and to check the accuracy of empirical formulas. Any numerical method for characterization needs to be as efficient and economical as possible in both CPU time and temporary storage requirement, although recent rapid advances in computers impose less severe restrictions on the efficiency and economy of the method. Another important aspect in the development of numerical methods has been the versatility of the method. In reality, however, numerical methods are chosen on the basis of trade-offs between accuracy, speed, storage requirements, versatility, etc. and are often structure dependent. The extensive recent developments in the area of time-domain numerical methods have established them among the major simulation, modelling and optimization tools, especially for ultrawideband and mixed-domain (solid-state, electromagnetic, digital, mechanical, thermal) components and modules, since they offer a very accurate representation of the real time-domain field variations. Their—mostly—parallelized nature enables their further acceleration with the aid of modern multiprocessor computers and modern parallelized computer cluster environments. The Sixth International Workshop on Computational Electromagnetics in the Time-Domain was held at Georgia Tech, Atlanta, GA, U.S.A., in 12–14 September 2005. It was attended by researchers around the globe, including Canada, France, Germany, Japan, United Kingdom, South Korea and United States. This Special Issue is a selection of the papers presented in the workshop. It represents part of the current progress and state-of-the-art in time-domain electromagnetic computational techniques. The first paper by Essakhi et al. discusses the global time-domain circuit simulation of a microwave rectenna. Next, a paper by Bommaraju et al. introduces a novel low-dispersive (2, 2) collocated FDTD scheme, while a paper by Ahmed et al. deals with improved-accuracy ADI-FDTD methods. The following paper by Carrion et al. proposes a new PML termination of conductive media for FDTD simulations for Bodies of Revolution. Chu et al. report in their paper the design of microwave structures combining MEFISTO-3D NOVA and MATLAB toolboxes. The next two papers focus on developments concerning TLM. Biwojno et al. [CEM-TD 2005 Best paper award] describe the development of a TLM mode with arbitrary embedded objects, while Lukashevich et al. introduce system identification and model order reduction to the TLM analysis. Last, but not least, Il-Suek Koh et al. give an overview of a semi-analytical time-domain formulation for low-frequency scattering. I would like to close with special acknowledgements to Dr Wolfgang Hoefer for his very insightful advise concerning the planning and the organization of the conference, to Dr Daniela Staiculescu for her valuable help with the review process of the submitted papers to this special issue and to Dr Samir El-Ghazaly for co-chairing the conference. We hope that this Special Issue provides readers with useful information on the CEM-TD and an additional motivation for the participation in the next CEM-TD conference to be held in Perugia, Italy on 15–17 October 2007.

A Quasi-Newton Preconditioned Newton–Krylov Method for Robust and Efficient Time-Domain Simulation of Integrated Circuits With Strong Parasitic Couplings

In this paper, the Newton-Krylov method is explored for robust and efficient time-domain simulation of integrated circuits with large amount of parasitic elements. Different from LU-factorization-based direct methods used in SPICE-like circuit simulators, the Newton-Krylov method uses a preconditioned Krylov-subspace iterative method for solving linearized-circuit equations. A key contribution of this paper is to introduce an effective quasi-Newton preconditioning scheme for Krylov-subspace methods to reduce the number and cost of LU factorization during an entire time-domain circuit simulation. The proposed quasi-Newton preconditioning scheme consists of four key techniques: 1) a systematic method for adaptively controlling time step sizes; 2) automatically generated piecewise weakly nonlinear (PWNL) definition of nonlinear devices to construct quasi-Newton preconditioners; 3) low-rank update techniques for incrementally updating preconditioners; and 4) incomplete-LU preconditioning for efficiency. Experimental results on a collection of digital, analog, and RF circuits have shown that the quasi-Newton preconditioned Krylov-subspace method is as robust and accurate as the direct method used in SPICE. The proposed Newton-Krylov method is attractive for simulating circuits with massive parasitic RLC elements for postlayout verification. For a nonlinear circuit with power/ground networks with tens-of-thousand elements, the CPU time speedup over SPICE3 is over 20X, and it is expected to increase further with the circuit size

Ideal switch model cuts simulation time

Considering the fact that any circuit containing an ideal switch is nonlinear, we developed a model for the ideal switch that is applicable in a general-purpose time-domain circuit simulation program. The switch is considered as a circuit element and used simply as any other circuit element. This model is simple to implement in a simulation program and it avoids numerical instability. One of its most important properties is that it handles difficult situations such as managing the Dirac pulse that is encountered when switching off a real inductance

An Enhanced Time-Domain Circuit Simulation Technique Based on LIM

In this paper, we show the generalized method of the time-domain circuit simulation based on LIM. Our method is applicable to any structure of circuits by combination with the SPICE-like method. In order to show the validity and efficiency of our method, an example circuit is simulated and the proposed method is compared with the conventional ones.

Interpolation and reinitialization in time-domain simulation of power electronic circuits

This paper presents a new interpolation–reinitialization method for transient simulations in both forced commutation and natural commutation conditions occurring in power electronic circuits. Recently published methods in this field are also discussed. The objectives are to provide generalization and to increase the precision level of numerical methods used for the computation of transients due to switching events in Electromagnetic Transients Program (EMTP) type applications.