Twisted differential line structure on high-speed printed circuit boards to reduce crosstalk and radiated emission

Differential signaling has become a popular choice for high-speed digital interconnection schemes on printed circuit boards (PCBs), offering superior immunity to crosstalk and external noise. However, conventional differential lines on PCBs still have unsolved problems, such as crosstalk and radiated emission. When more than two differential pairs run in parallel, a line is coupled to the line adjacent to it because all the lines are parallel in a fixed order. Accordingly, the two lines that constitute a differential pair are subject to the differential-mode crosstalk that cannot be canceled out by virtue of the differential signaling. To overcome this, we propose a twisted differential line (TDL) structure on a high-speed multilayer PCB by using a concept similar to a twisted pair in a cable interconnection. It has been successfully demonstrated by measurement and simulation that the TDL is subject to much lower crosstalk and achieves a 13-dB suppression of radiated emission, even when supporting a 3-Gb/s data rate.     

Finite element method applied to stress simulation of high power 980nm pump lasers

A three dimensional analysis on stress and strain in the central and in the mirror area of a InGaAs---GaAs ridge laser diode structure is presented. The analysis is based on a finite element method model, which couples thermal behaviour of laser to its mechanical structure. The impact of process parameters on reliability of device is discussed, and results are given for process and operation induced stress.     

Simplified modeling of parallel plate resonances on multilayerprinted circuit boards

Multilayer printed circuit boards (PCBs) are currently used in various areas of electronics such as telecommunications. However, high crosstalk between signal vias can cause degradation of performance for these kinds of structures. Resonances of parallel ground or power planes can increase this crosstalk. In this study, a simplified approach to the modeling of these resonances is described. It is assumed that the fields inside the board have characteristically only two-dimensional (2-D) variation. When this hypothesis is valid, it is shown that resonances can be measured on two-layer prototyping boards and simulated using a 2-D finite-difference model. It is additionally noted that a previously suggested method of using coaxial ground vias to suppress coupling between vias is not necessarily effective if there are resonant parallel plates on the board. Agreement between measured and modeled results is good enough for practical design purposes. The main advantages of the method used in this study compared to the more robust three-dimensional (3-D) simulation models are savings in time and costs. Additionally, prototyping is much easier on two than multilayer boards     

A new twisted differential line structure on high-speed printed circuit boards to enhance immunity to crosstalk and external noise

Differential signaling has become a popular choice for high-speed interconnection schemes on Printed Circuit Boards (PCBs), offering superior immunity to external noise. However, conventional differential transmission lines on PCBs have problems, such as crosstalk and radiated emission. To overcome these, we propose a Twisted Differential Line (TDL) structure on a multilayer PCB. Its improved immunity to crosstalk noise and the reduced radiated emission has been successfully demonstrated by measurement. The proposed structure is proven to transmit 3 Gbps digital signals with a clear eye-pattern. Furthermore, it is subject to much less crosstalk noise and achieves a 13 dB suppression of radiated emission.     

Extended chaos control method applied to Chua circuit

An extended chaos control strategy, based on previous work, is developed and applied to a real implementation of Chua's circuit. The new approach leads to improvements in the stability and controllability of this electronic oscillator, which has been used to study secure communication systems     

Finite element modeling in surgery simulation

Modeling the deformation of human organs for surgery simulation systems has turned out to be quite a challenge. Not only is very little known about the physical properties of general human tissue but in addition, most conventional modeling techniques are not applicable because of the timing requirements of simulation systems. To produce a video-like visualization of a deforming organ, the deformation must be determined at rates of 10-20 times/s. In the fields of elasticity and related modeling paradigms, the main interest has been the development of accurate mathematical models. The speed of these models has been a secondary interest. But for surgery simulation systems, the priorities are reversed. The main interest is the speed and robustness of the models, and accuracy is of less concern. Recent years have seen the development of different practical modeling techniques that take into account the reversed priorities and can be used in practice for real-time modeling of deformable organs. The paper discusses some of these new techniques in the reference frame of finite element models. In particular, it builds on the recent work by the author on fast finite element models and discusses the advantages and disadvantages of these models in comparison to previous models     

Finite element modeling of electronic packages subjected to drop impact

As more electronic products become portable, many product manufacturers have started to pay more attention to the robustness of their products. Finite element (FE) simulation has become increasingly popular in the analysis of products subjected to impact loading. The need for details in a FE mesh is always balanced by considerations of simulation time and available computational resources. In this paper, three commonly used approaches to FE modeling of a ball grid array (BGA) package subjected to drop impact are evaluated. The first model comprises a detailed mesh of the printed circuit board (PCB), integrated circuit (IC) package and interconnecting solder balls using solid three-dimensional (3-D) elements. The degrees of freedom is reduced for the second mesh by using shell elements for the PCB and IC package while retaining the detailed mesh of the solder balls using solid 3-D elements. The third mesh is a further simplification of the second mesh whereby the solder balls are replaced by a single beam element each. The stresses within the solder balls are then obtained in a separate FE analysis of a detailed solder ball mesh using the displacement history of nodes around the beam elements from the previous analysis as inputs. Solder ball stresses from all three meshes were found to differ by as much as 40% although PCB deflection compared favorably.     

Finite difference modelling of moisture diffusion in printed circuit boards with ground planes

A finite difference model has been applied to diffusion modelling of molecular moisture diffusion in Printed Circuit Boards (PCB) that have ground planes. Capacitance measurements between two ground planes within a PCB during moisture uptake and removal allowed diffusion coefficients to be determined. These diffusion coefficients were then used to look at the effect of ground plane width, hole density and meshed ground plane dimensions on bake time. The effect of plating holes on the bake time has also been investigated. Results show that whilst a few hours are sufficient to bake PCBs with no ground planes, days, or even months are required to remove moisture from within ground planes due to the extra perpendicular distance the moisture must diffuse. The results demonstrate the importance of storage conditions of the PCB, as once moisture has diffused into a board with ground planes; it is often not feasible to remove it.     

Characterization and modeling of a new via structure in multilayered printed circuit boards

We demonstrate that structure engineering of the transmission line near the via can reduce the amount of reflection of the RF signal. We have fabricated two types of vias with different transmission line geometries and have measured the reflection. The measured results show that the shape of the transmission line near the via hole is important in determining the total reflection of the via structure. The amount of reflection obtained from full three-dimensional (3-D) electromagnetic simulations can reproduce the measured results with reasonable accuracy, which suggests that efficient design of the via structure could be possible without resorting to hardware fabrication and characterization.     

Finite element modeling of capacitive coupling voltage contrast

Capacitive coupling voltage contrast (CCVC) is proven to be able to detect broken track in high density organic substrate with solder mask on top of the tracks. In this work, we develop a finite element model to solve the electromagnetic equations and determine the surface voltage of the solder mask under the interaction of the electron beam and the electrostatic induction due to the biasing of the underlying track. As the brightness of an image under SEM depends on the surface voltage of the object under observation, our model is able to explain the experimental observations of CCVC accurately. This model also examines the limitation of the CCVC.     

Finite element modeling of a polarization independent opticalamplifier

Polarization independent amplifiers are studied using a perturbation technique based on the finite element method (FEM). The need for such a sophisticated technique to tackle this practical problem is noted and the impact of user-friendly interfaces is discussed. A function evaluator module, FUNBOX, is used to assess mode overlap integrals and the confinement factor. The FEM is used here to estimate waveguide/amplifier coupling loss, coupling to higher order modes and the polarization sensitivity of an amplifier structure. The result of a tolerancing exercise are presented, indicating the power and usefulness of such modeling tools     

Vector circuit method applied for chiral slab waveguides

Eigenvalue equations for the propagation constants of lightwaves in open chiral slab waveguides are derived. The analysis makes use of vector circuit modeling of a chiral slab, the method which has been previously applied for calculating reflection and transmission of electromagnetic waves in chiral multilayer structures. The general eigenvalue equation for the guide which is valid for arbitrary boundary impedance conditions on the slab interfaces is derived, and three special cases are analyzed in detail: an open chiral dielectric slab with dielectric half spaces of the opposite sides of the slab, a chiral slab on an ideally conducting surface, and a chiral slab on an ideal magnetic surface. The theory is visualized by calculated dispersion curves indicating the chirality effect on the wave propagation characteristics     

Simulation and modeling of the effect of substrate conductivity on coupling inductance and circuit crosstalk

The goal of this work was to simulate the effect of the finite conductivity of semiconductor substrates on the on-chip coupling inductance and then to investigate the effect of the on-chip coupling inductance on circuit crosstalk. In addition, the limitations of standard approaches for estimating coupling inductance are examined. A method for the reduction of the coupling inductance and its effect on circuit crosstalk is also discussed.     

MOSFET modeling for analog circuit CAD: problems and prospects

The requirements for good MOSFET modeling are discussed, as they apply to usage in analog and mixed analog-digital design. A set of benchmark tests that can be easily performed by the reader are given, and it is argued that most CAD models today cannot pass all the tests, even for simple, long-channel devices at room temperature. A number of other problems are discussed, and in certain cases specific cures are suggested. The issue of parameter extraction is addressed. Finally, the context of model development and usage is considered, and it is argued that some of the factors responsible for the problems encountered in the modeling effort are of a nontechnical nature     

Finite element modeling and multigrid preconditioner using adaptive triangular meshes

The letter describes a finite element method (FEM) using adaptive triangular meshes for the modeling of microwave devices. A robust preconditioning technique is provided for the fast solution of the resultant FEM matrix equations. The proposed preconditioner is based on a multigrid scheme for the vector-scalar potential FE formulation of the electromagnetic problem. Numerical experiments demonstrate its superior numerical convergence.     

Finite element modeling of electrode-skin contact impedance inelectrical impedance tomography

In electrical impedance tomography (EIT), the measured voltages are sensitive to electrode-skin contact impedance because the contact impedance and the current density through it are both high. Large electrodes were used to provide a more uniform current distribution and reduce the contact impedance. A large electrode differs from a point electrode in that it has shunting and edge effects that cannot be modeled by a single resistor. The finite-element method (FEM) was used to study the electric field distributions underneath an electrode, and three models were developed: a FEM model, a simplified FEM model, and a weighted load model. The FEM models considered both shunting and edge effects and closely matched the experimental measurements. It is concluded that FEM models of electrodes can be used to improve the performance of an electrical impedance tomography reconstruction algorithm     

Finite element method using port truncation by perfectly matchedlayer boundary conditions for optical waveguide discontinuity problems

A powerful algorithm based on a finite element method (FEM) is newly formulated for the analysis of waveguide discontinuities. In an earlier approach, FEM was applied to the finite region with discontinuities, and a mode expansion technique was applied to the uniform waveguides that are connected to the input and output ports of finite region. Although, in the present approach, the uniform waveguides are replaced by perfectly matched layer (PML) boundary conditions, it is possible to treat periodically varying waveguide structures such as photonic crystal (PC) waveguides. A combined method of beam propagation method (BPM) and FEM is also shown in such a form that a mode expansion technique is not required. To show the validity and usefulness of the present approach, numerical examples for optical gratings, circuit components based on PC waveguides and optical directional couplers are presented     

Simple method for mitigation of polarization crosstalk in silica planar lightwave circuit directional couplers

Polarization crosstalk in planar lightwave circuit directional couplers can cause significant polarization-dependence in interferometers that use them. We show a simple way to mitigate the polarization crosstalk without incurring a performance penalty or requiring extra fabrication steps. We demonstrate it on a 23-ps Mach-Zehnder delay interferometer.     

一种PCB表观检查机的无阴影高均匀照明方法

印刷电路板(PCB)表观检查机的检测算法,对亮度不均的阴影条纹的原始图像难以处理,最终影响PCB的检测性能。本文基于实验图像阴影条纹的形成机理,提出一种无阴影高均匀的PCB表观检查机照明方法。本方法采用4个荧光灯组成,其中两个光源与物面的镜面方向对称,用于高反射照明;另外两个光源用于漫反射照明。仿真和实验表明,本方法可以消除高反射曲面引起的图像阴影条纹,在PCB表观检查机系统中达到均匀照明效果且增强缺陷和背景的对比度。本方法也可应用于类似的高反射曲面的自动表观检查系统,如铝带缺陷检查,塑料薄膜缺陷检查等。