Osami Wada

Convergence acceleration and accuracy improvement in power bus impedance calculation with a fast algorithm using cavity modes

Based on the cavity-mode model, we have developed a fast algorithm for calculating power bus impedance in multilayer printed circuit boards. The fast algorithm is based on a closed-form expression for the impedance Z matrix of a rectangular power bus structure; this expression was obtained by reducing the original double infinite series into a single infinite series under an approximation. The convergence of the single series is further accelerated analytically. The accelerated single summation enables much faster computation, since use of only a few terms is enough to obtain good accuracy. In addition, we propose two ways to compensate for the error due to the approximation involved in the process of reducing the double series to the single series, and have demonstrated that these two techniques are almost equivalent.

A simple method for measuring the relative permittivity of printed circuit board materials

This paper presents a simple method to measure the relative permittivity of glass-epoxy printed circuit boards (PCBs). In this method, the relative permittivity as a function of frequency is measured using an actual PCB. In order to estimate the relative permittivity, the reflection coefficient is measured with a network analyzer. The relative permittivity is calculated by observing the frequencies of the resonant cavity modes. We show that the relative permittivity of an FR-4 sample decreases from 4.3 to 4.2 at frequencies from 300 MHz to 2 GHz.

Power current modeling of IC/LSI with load dependency for EMI simulation

In this paper, we describe how we modeled EMI noise from the power-pin current of an LSI that has two ports: a power-ground port and a driver output port. We named this modeling the Linear Equivalent Circuit and Current Source for I/O (LECCS-I/O) model and with it measured power current and power-ground impedance for various combinations of loading capacitances and decoupling inductances using a small scale IC (74LVC04). Results showed that up to 500 MHz, the LECCS-I/O model could predict peak and valley frequencies of the power current where the error was within 2.5 MHz, and where the peak current error was less than 5 dB. The application range of the LECCS-I/O model is valid where the non-overlap duration of the dumping oscillation wave between cycles is longer than twice the time constant of the waveform.

High-speed simulation of PCB emission and immunity with frequency-domain IC/LSI source models

Some recent results from research conducted in the EMC group at Okayama University are reviewed. A scheme for power-bus modeling with an analytical method is introduced. A linear macro-model for ICs/LSIs, called the LECCS model, has been developed for EMI and EMS simulation. This model has a very simple structure and is sufficiently accurate. Combining the LECCS model with analytical simulation techniques for power-bus resonance simulation provides a method for high-speed EMI simulation and decoupling evaluation related to PCB and LSI design. A useful explanation of the common-mode excitation mechanism, which utilizes the imbalance factor of a transmission line, is also presented. Some of the results were investigated by implementing prototypes of a high-speed EMI simulator, HISES.

Application of segmentation method to analysis of power/ground plane resonance in multilayer PCBs

The fast algorithm developed for calculating the resonant characteristics of the power/ground planes in multilayer PCBs, is extended to the case of that the pattern of the power/ground planes consists of several segments of rectangles, using the so-called segmentation method. Good agreements between the calculated and measured results have demonstrated the usefulness and accuracy of our fast algorithm and the segmentation method.

Estimation of common-mode EMI caused by a signal line in the vicinity of ground edge on a PCB

The authors have developed an estimation method of common mode radiation from a PCB. A parameter named current division factor explains a generation mechanism of the common mode. Rigorous analysis, instead of rough approximation, is required to calculate the factor for an asymmetric structure. A 2-dimensional static electric field analysis by the boundary element method (BEM) is applied to this calculation, which requires less time than 3-dimensional simulations. EMI increases when the signal line comes close to the edge of ground pattern. The effect is evaluated with the simulation of the factor. The estimation agrees well with measurement within 1 dB.

Power current model of LSI and parameter identification for EMI simulation of digital PCBs

A power current model of LSIs for EMI simulation of digital printed circuit boards, and a parameter identification method based on the model are presented. The model consists of equivalent internal impedance and an equivalent internal current source. The equivalent internal impedance is obtained by measuring the impedance between the power and ground terminal of an LSI by means of an impedance analyzer, and an equivalent internal source is obtained from the measured current through the power terminal under the conditions of known external impedance. Furthermore, it is shown that simulation results generated using this model have good agreement with the results of measurements made under a range of external impedances.

Analysis of resonance characteristics of a power bus with rectangle and triangle elements in multilayer PCBs

One of the major sources of radiated EMI is attributed to power bus resonance in a printed circuit board (PCB). A fast algorithm, combined with the segmentation method, is applied for calculating resonance characteristics of a power bus whose pattern consists of several segments of rectangles and/or right-angled triangles. Good agreement between the calculated and measured results demonstrates the usefulness and accuracy of the fast algorithm and the segmentation method.

SUPPRESSION OF THE ETALON FRINGE IN ABSORPTION SPECTROMETRY WITH AN INFRARED TUNABLE DIODE LASER

A polarization control method is applied to suppress the e´ talon fringe, and experimental results are described. It is found that this method can suppress an e´ talon fringe of the order of 102-6 in terms of the equivalent absolute absorption value, 1/100 of the off-controlled condition. This technique enables our tunable diode laser absorption spectrometry (TDLAS) system to measure atmospheric methane of about 2 ppmv concentration with ambiguity within 102-4 ppmv (0.1 ppbv). This scheme is useful for the portable TDLAS systems because of its simplicity.

A design method of decoupling circuits for a digital PCB to reduce high frequency current on power and ground planes

This paper describes a design technique of decoupling circuits that can reduce high frequency current rushing into the power/ground planes of a digital PCB. In this technique, the IC is modeled as a current source of high frequency, and a parameter that represents the effect of the high frequency current reduction is derived. Then, by using the parameter, a design procedure to obtain the optimal bypass capacitor and the decoupling inductor is shown. Furthermore, validity of this modeling is shown by experimental study.