Lumped-element Finite-difference Time-domain Research Articles

Finite-Difference Time-Domain Simulation of Arbitrary Impedance using One Port S-Parameter

Many modern radio-frequency devices comprise both lumped-element components and complex geometries. Simulation of such a device requires modeling the electromagnetic interactions with both geometric features and lumped components. We present a method for including arbitrary lumped-element components into finite-difference time-domain (FDTD) simulations. The lumped-element components, which are described by their scattering parameters, are modeled in the Yee grid as dependent voltage sources. The mathematical formulation is described, along with its implementation into a FDTD simulator. For verification, simulation results of resistive, capacitive, and inductive loads are presented, and are compared to simulation results from previous lumped-element FDTD methods. This represents a first-step in modeling multiport networks described by their scattering parameters.

Direct Incorporation of Scattering Parameters Into the FDTD Algorithm

A direct method for incorporating S-parameters into an finite-difference time-domain (FDTD) algorithm is presented in this paper. The frequency-domain S-parameters of an arbitrary network to be embedded within an electromagnetic system are represented as a series of modified impulse responses using a nonuniform discrete-time technique. In this way, the currents passing through the embedded network can be calculated using a convolution in the time-domain. The calculated currents are used to update the electric fields at the locations occupied by the embedded network according to Ampere's law. The simulation results using this method have been compared with the results simulated by Lumped-Element FDTD method (LE-FDTD), showing very good agreement. The method presented here is highly accurate and stable, and is suitable for use in quite general cases, especially where the embedded network cannot easily be represented by lumped elements.

Wide‐band modelling of CMOS interconnections and voiding damages with the lumped element LE‐FDTD method

AbstractThis paper illustrates the application of a lumped element‐finite difference time domain (LE‐FDTD) simulator to the wide‐band modelling of CMOS interconnections. To achieve very accurate results the short‐open calibration (SOC) technique has been adopted. Specific parameters of a CMOS interconnection laterally screened by a stack of metal vias have been extracted in the two cases of an unperturbed and a purposely damaged metal line. The behaviour of void‐like defects in the metal line has been also studied using the fully three‐dimensional capabilities of the simulator. It has been demonstrated that, at least in the simulated cases, only the specific resistance is affected by damaging. Copyright © 2004 John Wiley & Sons, Ltd.

On the numerical errors induced by the space-time discretization in the LE-FDTD method

In this work, the accuracy of the lumped element finite-difference time-domain (LE-FDTD) method is discussed in the particular case of a planar distribution of equal resistors. Following the von Neumann technique and assuming a uniform grid, the effective impedance of the lumped resistor has been rigorously derived in a closed form. The result obtained has been compared with the LE-FDTD simulation of a simple test structure. This structure consists of an infinitely long parallel-plate waveguide loaded with the planar distribution of resistors. The excellent agreement obtained validates the approach showing a dependence of the effective resistor impedance on spatial and temporal discretization steps.

Computation of electromagnetic field inside a tissue at mobile communications frequencies

The increasing diffusion of mobile communications is stimulating the study of the interaction mechanisms between electromagnetic (EM) fields and biological systems at radio frequencies. This paper is devoted to the modeling of the interaction between EM fields and a tissue, represented with spherical cells. Different EM approaches have been used to analyze the problem and, in particular, the lumped-element finite-difference time-domain (FDTD) technique has been used to model the cell's membrane represented with the Hodgkin-Huxley (HH) model, and the Floquet theorem to study a tissue by analyzing only few cells. The EM problem has been solved by using the FDTD technique to be independent from the geometry. Computations have been performed at GSM900 and GSM1800 frequencies overcoming the problem relevant to the computation time by using the quasi-static FDTD technique. The results show the field distribution inside the tissue at GSM frequencies; the effect of the application of the HH model to the membrane is also shown.

Global modeling strategies for the analysis of high-frequency integrated circuits

In this paper, a simulator based on a global electromagnetic model is presented, suited for the analysis of HF integrated and hybrid electronic circuits. The model is based on the self-consistent solution of Maxwell's equation and of semiconductor transport equations, exploiting a generalized finite-difference time-domain (FDTD) scheme. The tool is, therefore, capable of accounting, on a distributed basis, for actual interactions between wave propagation and charge transport, anti is capable of providing a physically based picture of traveling-wave semiconductor devices. The implementation is such that more conventional algorithms (e.g. lumped-element FDTD or plain FDTD) can be regarded as a subset of the global scheme itself. This makes it possible to intermix different physical models, featuring different degrees of physical accuracy and computational efficiency, within the same simulation environment. Main features of such an environment are described by means of the simulation of a simple 76-GHz distributed switch.

A new algorithm for the incorporation of arbitrary linear lumped networks into FDTD simulators

The inclusion of lumped elements, both linear and nonlinear, into the finite-difference time-domain (FDTD) algorithm has been recently made possible by the introduction of the lumped element FDTD method. Such a method, however, cannot efficiently and accurately account for two-terminal networks made of several lumped elements, arbitrarily connected together. This limitation can be removed as proposed in this paper by describing the network in terms of its impedance in the Laplace domain and by using appropriate digital signal-processing methodologies to fit the resulting description to Yee's algorithm. The resulting difference equations allow an arbitrary two-terminal network to be inserted into one FDTD cell, preserving the full explicit nature of the conventional FDTD scheme and requiring a minimum number of additional storage variables. The new approach has been validated by comparison with the exact solution of a parallel-plate waveguide loaded with lumped networks in the transverse plane.

Integrated FDTD and solid-state device simulation

A mixed-mode circuit simulation technique is presented, based on the lumped-element finite-difference time-domain (FDTD) scheme. The algorithm is extended to incorporate numerical models of lumped devices. This makes the formulation and characterization of analytical, closed-form models for circuit devices unnecessary and allows for directly correlating device behavior and fabrication process parameters. The code is therefore especially suited for high-speed and microwave IC optimization.

Accurate and efficient circuit simulation with lumped-element FDTD technique

A three-dimensional (3-D) implementation of the lumped-element finite-difference time-domain (FDTD) algorithm has been carried out. To accomplish proper description of device dynamic responses, the code incorporates accurate models of lumped bipolar devices, including nonlinear capacitances associated with pn and Schottky junctions. The nonlinear system arising from discretized lumped-element equations is solved by means of an iterative Newton-Raphson algorithm, the convergence properties of which are sensitive to the value of the simulation time step. The computational efficiency of the algorithm (as well as its robustness) has significantly been enhanced by introducing an adaptive time-step algorithm, which dynamically adjusts the time-step itself to ensure convergence during the simulation. Several simulation examples are compared with conventional analysis techniques and demonstrate the algorithm reliability as well as its increased efficiency.