Very fast and accurate modeling of multilayer waveguiding photonicbandgap structures

A model of one-dimensional (1-D) waveguiding photonic bandgap (PBG) structures, based on leaky mode propagation (LMP) method, is proposed for the first time. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, has been carried out for a finite extension configuration. The numerical results have been compared with those obtained by using other methods, showing a very good agreement together with some significant advantages in terms of very low computational time, absence of any a priori theoretical assumptions and approximations, capability of simulating the actual behavior of the device as a reflector, and fast determination of the bandgap position     

Investigation of 3D semivectorial finite-difference beampropagation method for bent waveguides

A three dimensions of semivectorial finite difference beam propagation method (FD-BPM) in cylindrical coordinates is investigated in order to analyze the optical wave propagation in the bent waveguides with the strong lateral confinement which will keep low radiation loss. The three dimensional (3D) semivectorial wave propagation equation is programmed in the quick and unconditionally stable procedure by using the alternating direction implicit method. This version of FD-BPM could well express the polarization characteristics of modal field near the dielectric interfaces and accurately simulate the wave propagation in bent waveguides even at a very small radius (<100 μm). Moreover, it is pointed out that the numerical precision of the algorithm is intensively affected by the propagation loss of bent waveguides along with the propagation step length of beam propagation method     

Efficient interface conditions for the finite difference beampropagation method

It is shown that by adapting the refractive indexes in the vicinity of interfaces, the 2-D beam propagation method based on the finite-difference (FDBPM) scheme can be made much more effective. This holds especially for TM modes propagating in structures with high-index contrasts, such as surface polaritons. A short discussion is given on the applicability of the FDBPM     

Complex propagators for evanescent waves in bidirectional beampropagation method

Existing algorithms for bidirectional optical beam propagation proposed to simulate reflective integrated photonic devices do not propagate evanescent fields correctly. Thus inaccuracy and instability problems can arise when fields have significant evanescent character. We propose complex representations of the propagation operator by choosing either a complex reference wave number or a complex representation of Pade approximation to address this issue. Therefore correct evolution of both propagating waves and evanescent waves can be simultaneously realized, significantly reducing the inaccuracy and instability problems. Both test problems and practical problems are presented for demonstration     

Modal fields calculation using the finite difference beampropagation method

A method is described to construct modal fields for an arbitrary one- or two-dimensional refractive index structure. An arbitrary starting field is propagated along a complex axis using the slowly varying envelope approximation (SVEA). By choosing suitable values for the step-size, one mode is maximally increased in amplitude on propagating, until convergence has been obtained. For the calculation of the next mode, the mode just found is filtered out, and the procedure starts again. The method is tested for one-dimensional refractive index structures, both for nonabsorbing and for absorbing structures, and is shown to give fast convergence     

State-space Integral-equation method for the S-domain modeling of planar circuits on semiconducting substrates

This paper presents a new and very efficient integral method for the electromagnetic modeling of planar circuits on multilayered semiconducting substrates. Differently from standard integral approaches, the method leads to a state-space model of the circuit. This model directly permits to find the admittance matrix in the form of a reduced-order pole expansion in the S-domain through standard Krylov sub-space techniques. Three examples demonstrate the really good performances of the method in terms of accuracy and rapidity.     

基于物理结构的GaN HEMTs小信号等效电路的精确建模方法研究

为了有效地表征GaN HEMTs在微波频段下的电学特性,研究了其高频等效电路的精确建模方法。基于GaN HEMTs器件的本征物理结构,综合考虑器件在制版过程中由电极和通孔所带来的寄生特性,描述了一种具有26个详细参数网络的小信号等效电路模型。此模型考虑了器件在工作环境下所受到的集肤效应,同时通过对小信号等效电路进行双端口网络参数分析,推导了其准静态近似的微波等效电路参数直接提取的简化算法,最终通过ADS仿真平台将所建模型和传统模型的S参数模拟结果与实测数据的一致性进行对比,验证了小信号等效电路模型的精确性与参数提取算法的有效性。     

Efficient and accurate modeling of planar anisotropic microwavestructures by the method of lines

A new algorithm for the analysis of planar microwave structures with anisotropic substrates is proposed and substantiated. This algorithm is based on generalized transmission-line (GTL) equations, which are developed here for numerical algorithms. For the purpose of analysis, two different modal matrices for the discretized transverse electric and magnetic fields are calculated. Furthermore, impedance/admittance transformation formulas are developed with the help of the GTL equations for longitudinal sections and general junctions. Crossed discretization lines are used in the latter case. The materials are assumed to be biaxial or specific anisotropic. Special algorithms are developed for junctions consisting of more than two waveguides in the cross section and for bends. The proposed algorithm is verified by numerical results     

Hierarchical fault modeling for linear analog circuits

This paper presents a hierarchical fault modeling approach for catastrophic as well as out-of-specification parametric faults in analog circuits. These include both, ac and dc faults in passive as well as active components. The fault models are based on functional error characterization. Case studies based on CMOS and nMOS operational amplifiers are discussed, and a full listing of derived behavioral fault models is presented. These fault models are then mapped to the faulty behavior at the macro-circuit level. Application of these fault models in an efficient fault simulator for analog circuits is also described.     

A new finite-difference-based method for wide-angle beam propagation

A novel split-step finite-difference method for wide-angle beam propagation is presented. The formulation allows solution of the second-order scalar wave equation without having to make the slowly varying envelope and one-way propagation approximations. The method is highly accurate and numerically efficient requiring only simple matrix multiplication for propagation.     

An accurate analytical propagation delay model for high-speed CMLbipolar circuits

A new analytical delay model for high-speed CML circuits is presented. It is applicable to high-speed/low-voltage-swing silicon and HBT CML circuits operating at medium or high current densities. The model is based on bipolar SPICE parameters file, and can be used to estimate the propagation delay time of CML circuits under different operating conditions. The detailed transient analysis accounts for delay components due to each element in the complete SPICE bipolar transistor model. The comparison to SPICE circuit simulation results show excellent agreement for a wide range of state-of-the-art technologies and circuit parameters. The new model predicts the delay time with less than 5% error in most cases. The influence of the finite slopes (slewing rate) of the input signal and the device dimensions is also investigated. The delay model determined the optimum current i₀ (or load resistor R_L) for a transistor of a certain emitter area when driven by a source of a voltage swing (ΔV) and slew time (t_r ). At a specified power dissipation, the delay model is used to optimally size the transistor emitter area for maximum switching speed. The model provides circuit and device guidelines to minimize the propagation delay time and improve the performance of high-speed CML circuits     

The modeling of resistive interconnects for integrated circuits

Techniques for analyzing the signal transmission properties of long resistive interconnects on integrated circuits are presented. Because accurate measurements of propagation characteristics on chip are difficult to make, RC transmission line theory is used to establish exact performance. The results of various simulations are compared to this theoretical performance. Guidance is provided for selecting the number of elements needed to accurately simulate performance under various conditions.     

A new technique for accurate and stable modeling of arbitrarily oriented thin wires in the FDTD method

A subcell model for thin wires in the finite-difference time-domain method using modified telegraphers equations has been developed by Holland et al. (1981). In this paper, we present an extension of their algorithm, which allows arbitrarily located and oriented wires with respect to the Cartesian grid. This is important to be able to accurately model wires that cannot be aligned to the Cartesian grid, e.g., tilted wires and circular loop wires. A symmetric coupling between field and wires yields a stable time-continuous field-wire system and the fully discrete field-wire system is stable under a Courant-Friedrich-Lewy (CFL) condition. The accuracy and excellent consistency of the proposed method are demonstrated for dipole and loop antennas with comparisons with the method of moments and experimental data.     

Analysis of a polarization splitter with a multilayer filter using a Pade/spl acute/-operator-based power-conserving fourth-order accurate beam-propagation method

A (1,1) Pade/spl acute/-operator-based fourth-order accurate finite-difference beam-propagation method is described for the analysis of the transverse-magnetic (TM) wave, with an emphasis on power conservation. As an application, a polarization splitter with a multilayer filter is analyzed. Reflectivities of more than 98% for the transverse-electric wave and transmissivities of more than 94% for the TM wave are obtained over a wide wavelength range of 1.1-1.65 /spl mu/m.     

MOSFET thermal noise modeling for analog integrated circuits

The effects of device geometry, oxide thickness, and bias condition on the thermal noise of MOSFET's are investigated. The experimental results show that the conventional MOSFET thermal noise models do not accurately predict the thermal noise of MOSFET's. A model that is capable of predicting the thermal noise of both long and short channel devices in both the triode and saturation regions is presented. This model, which can be easily implemented into existing circuit simulators such as SPICE, has been verified by a wide variety of measurements     

Novel method for the analysis of RLC circuits

The lagrangian formulation of classical mechanics is applied to RLC circuits. The generalized power function is introduced and the reduced Lagrange equations are used in the analysis of the system. This new method seems to be more useful than the conventional Kirchhoff taws and Lagrange equations. This is illustrated by an example.     

Analysis of basic four-wave mixing characteristics in asemiconductor optical amplifier by the finite-difference beampropagation method

We have numerically analyzed nondegenerate four-wave mixing (FWM) among short optical pulses in a semiconductor optical amplifier (SOA) by the finite-difference beam propagation method (FD-BPM). We used the nonlinear propagation equation taking into account gain spectrum dynamic gain saturation which depends on carrier depression, carrier heating, and spectral hole-burning, group velocity dispersion, self-phase modulation, and two-photon absorption. To analyze FWM in an SOA, the evolution in time and spectral domain of two input optical pulses with different frequencies during propagation was calculated. From this simulation, it has become clear that the method me used here is a very useful technique for simulating FWM characteristics in SOA's. We also found that the wavelength dependence of the gain is crucial if the detuning is larger than 1 THz     

An accurate intrinsic capacitance modeling for deep submicrometerMOSFET's

This paper presents a new approach to the modeling of MOSFET capacitive characteristics for accurate simulation of deep submicrometer integrated circuits. The C-V characteristics of our new quasistatic intrinsic capacitance model accurately describes the short channel effects of deep submicrometer MOSFET's by accounting for velocity saturation and series resistance effects. The use of charge equations consistent with the short channel I-V characteristics leads to C-V characteristics which preserve all major short channel effects. The C-V calculation, based on nonpinned surface potential approach and drift-diffusion model, shows highly accurate short-channel effects and inherently smooth transitions for all conditions of device operation. The accuracy of the C-V characteristics has been demonstrated by comparison with the Ward-Dutton model and PISCES simulation results     

A design-oriented methodology for accurate modeling of on-chip interconnects

An accurate modeling methodology for typical on-chip interconnects used in the design of high frequency digital, analog, and mixed signal systems is presented. The methodology includes the parameter extraction procedure, the equivalent circuit model selection, and mainly the determination of the minimum number of sections required in the equivalent circuit for accurate representing interconnects of certain lengths within specific frequency ranges while considering the frequency-dependent nature of the associated parameters. The modeling procedure is applied to interconnection lines up to 35 GHz obtaining good simulation-experiment correlations. In order to verify the accuracy of the obtained models in the design of integrated circuits (IC), several ring oscillators using interconnection lines with different lengths are designed and fabricated in Austriamicrosystems 0.35 μm CMOS process. The average error between the experimental and simulated operating frequency of the ring oscillators is reduced up to 2% when the interconnections are represented by the equivalent circuit model obtained by applying the proposed methodology.     

Geometric modeling of nonlinear RLC circuits

In this paper, the dynamics of nonlinear RLC circuits including independent and controlled voltage or current sources is described using the Brayton-Moser equations. The underlying geometric structure is highlighted and it is shown that the Brayton-Moser equations can be written as a dynamical system with respect to a noncanonical Dirac structure. The state variables are inductor currents and capacitor voltages. The formalism can be extended to include circuits with elements in excess, as well as general noncomplete circuits. Relations with the Hamiltonian formulation of nonlinear electrical circuits are clearly pointed out.