Estimation of Printed Circuit Board Power Bus Noise at Resonance Using a Simple Transmission Line Model

The maximum coupling between printed circuit board components connected to the same power-ground plane pair often occurs at or near power bus resonances. Theoretically, the transfer coefficient, S 21 , between two locations on the power bus can be as high as 0dB (i.e. perfect coupling) near resonant frequencies. However, in practice the coupling is usually much less due to losses in the power bus structure. Determining exactly what the maximum coupling will be in a lossy power bus structure requires a numerical model or measurement. However, an estimation of the maximum coupling can be obtained by drawing an analogy between two-dimensional printed circuit board power buses and one-dimensional transmission lines. In this paper, a one-dimensional lossy transmission-line model is employed to simulate power-ground plane pairs and calculate S 21 between a noise source and a load. A simple formula for estimating the maximum coupling is derived from the transmission line model. This formula illustrates the effect that plane spacing, dielectric loss and board dimensions have on the maximum coupling between components attached to the same power bus structur

Investigation of Fundamental Mechanisms of Common-Mode Radiation from Printed Circuit Boards with Attached Cables

Fundamental mechanisms leading to common-mode radiation from printed circuit boards with attached cables have been studied. Two primary mechanisms have been identified, one associated with a differential-mode voltage that results in a common-mode current on an attached cable, and another associated with a differential-mode current that results in a common-mode current on the cable. The two mechanisms are demonstrated through numerical and experimental results

Identifying and Quantifying Printed Circuit Board Inductance

The concepts of inductance and partial inductance play a key role in printed circuit board (PCB) modeling. The inductance of the signal path is an important parameter in high-speed signal integrity calculations. Delta_I noise modeling, crosstalk calculations, and common-mode source identification all rely heavily on accurate estimations of the partial inductance associated with traces, vias, and signal return paths on printed circuit boards. The paper begins by identifying and quantifying the parameters that affect the inductance of typical PCB geometries. Closed-form equations are provided for estimating the partial inductances of simple trace, via, and ground plane configurations. Finally, the issue of current crowding around via connections in planes and its affect on the partial inductance of the plane is addressed

Power Bus Isolation Using Power Islands in Printed Circuit Boards

Power islands are often employed in printed circuit board (PCB) designs to alleviate the problem of power bus noise coupling between circuits. Good isolation can be obtained over a wide frequency band due to the large series impedance provided by the gap between the power islands. However, power bus resonances may degrade the isolation at high frequencies. The amount of isolation also depends on the type of connection between power islands and the components on the board. This paper experimentally investigates the effectiveness of several power island structures up to 3.0 GH

Designing Power Bus Decoupling for CMOS Devices

The adequacy of the DC power bus decoupling for CMOS devices can be determined if the effective board decoupling capacitance, the CMOS load capacitance, the CMOS power dissipation capacitance, the switching time, and the allowable bus noise voltage are known. A simple method is presented for estimating the effective decoupling capacitance. The load and power dissipation capacitance values are shown analytically and experimentally to be closely related to the transient current. The transient current and switching time are used to estimate the transient noise voltage on the power bu

An Expert System for Predicting Radiated EMI from PCB\u27s

This paper describes an expert systems approach, based on symbolic reasoning techniques, to the problem of predicting radiated EMI levels from printed circuit boards. The expert system, currently under development at the University of Missouri-Rolla, USA, starts by extracting board geometry information from the board layout files. This information is fed into the classification algorithm, which determines the signal properties and nature of each net, using the knowledge stored in the knowledge base. The evaluation algorithm uses the available in formation to identify and evaluate critical circuit geometries, and then estimates the effect that these geometries have on system radiation levels. The expert system also looks for violations of basic EMC design rules. The main advantage of such a system over conventional software is that the expert system does not require the user to be an expert in EMC or circuit design

Modeling Power Bus Decoupling on Multilayer Printed Circuit Boards

Power bus decoupling designs on multilayer printed circuit boards must adequately account for the power bus interplane capacitance and its consequences for the design. Lumped element models for a power bus on a multilayer printed circuit board where an appreciable or entire portion of a layer is devoted to power and ground have been developed. The models are applicable below the distributed resonances of the board. Analytical, circuit simulation, and experimental studies have been conducted to test the models, investigate the effects of the distributed interplane capacitance of the power bus, and the effect of interconnect inductance associated with surface-mount decoupling capacitors

Integrating Electromagnetic Compatibility Laboratory Exercises into Undergraduate Electromagnetics

A state-of-the art high-frequency laboratory is being developed for pursuing laboratory exercises in EMC. These exercises are being integrated into three undergraduate electromagnetics courses. Two of the courses are a required introductory sequence. The laboratory exercises are designed to stimulate students interest, motivate them to learn concepts, and provide them with exposure to practical EMC applications. Laboratory exercises are also an integral part of an EMC elective course. This paper describes the laboratory development and discusses experiments that can be integrated into these three courses for teaching fundamental electromagnetics as well as EMC