Bundled Cable Parameters and Their Impact on EMI Measurement Repeatability

EMI (electromagnetic interference) test procedures specify that long cables should be bundled at their center in some circumstances. The author investigates the effect of cable bundling using analytical models and measurements. He examines how cable bundle parameters such as length and tightness\u27\u27 can affect the repeatability of the measurement. Simple models of a bundled cable suggest that relatively small changes in the geometry of the bundle can significantly affect the common-mode cable current. Parameters such as length, tightness, location and the number of turns determine the impedance of the bundle. As the impedance of the cable bundle changes, the resonant frequency of the system shifts. This can result in large changes at the very frequencies where EMI problems are most likely to occur. It is also shown that lossy cables or cables with a lossy common-mode termination are less likely to be sensitive to minor changes in cable bundle parameters. The resonant peaks in a lossy system are smaller and cover a wider band of frequencies. Small shifts in the resonant frequency do not have as much of an impact on the currents induced at any one frequency

The Role of Component Packaging in System Electromagnetic Compatibility

Increases in the speed and density of electronic systems do not necessarily result in tougher electromagnetic compatibility problems. In fact, recent advances in packaging technology can help designers to meet electromagnetic compatibility requirements. However, working with new technologies requires us to re-evaluate existing EMC design models and guidelines. Understanding the system-level impact of component-level packaging changes, is a prerequisite for meeting stringent electromagnetic compatibility requirements in a timely and cost-effective manner

PCB EMC Design Guidelines: A Brief Annotated List

Some of the worst printed circuit board design choices are made by engineers who are trying to comply with a list of EMC design guidelines. Nevertheless, a short list of design guidelines can be helpful at times. This paper reviews some of the more general EMC design guidelines for printed circuit board layout

The Effect of Cable Terminations on EMI Measurements

The effects of using uncontrolled or undefined cable terminations during electromagnetic interference (EMI) measurements was investigated. Several different models are described along with corresponding measurements in order to illustrate how specific terminations can be used to achieve particular measurement goals. It is noted that until a well-defined method of terminating power and signal cables is introduced, the best the EMI test engineer can do is to be aware of the significance of common-mode terminations and try to avoid situations where the common-mode termination impedance is completely undefined or not repeatable

Printed Circuit Board EMI Source Mechanisms

This tutorial paper reviews the basic mechanisms by which signal voltages and currents on a printed circuit board produce unintentional radiated emissions

A Modular Approach to Numerical EM Modeling

Discusses the components of numerical EM modelling codes. The authors go on to discuss a modular approach to EM software development which would allow developers to focus on one component at a time. The modular approach relies on standard format input and output files for each component (or module) of the cod

Using an LU Recombination Method to Improve the Performance of the Boundary Element Method at Very Low Frequencies

Many numerical electromagnetic modeling techniques that work very well at high frequencies do not work well at lower frequencies. This is directly or indirectly due to the weak coupling between the electric and magnetic fields at low frequencies. One technique for improving the performance of boundary element techniques at low frequencies is through the use of loop-tree basis functions, which decouple the contributions from the vector and scalar electric potential. However, loop-tree basis functions can be difficult to define for large, complex geometries. This paper describes a new method for improving the low-frequency performance of boundary element techniques. The proposed method does not require special basis functions and is relatively easy to implement. Numerical errors introduced by the great difference in scale between the vector and scalar electric potential are corrected automatically during the LU decomposition of the impedance matrix

Circuit Models for Power Bus Structures on Printed Circuit Boards using a Hybrid FEM-SPICE Method

Power bus structures consisting of two parallel conducting planes are widely used on high-speed printed circuit boards. In this paper, a full-wave finite-element method (FEM) method is used to analyze power bus structures, and the resulting matrix equations are converted to equivalent circuits that can be analyzed using SPICE programs. Using this method of combining FEM and SPICE, power bus structures of arbitrary shape can be modeled efficiently both in the time-domain and frequency-domain, along with the circuit components connected to the bus. Dielectric loss and losses due to the finite resistance of the power planes can also be modeled. Practical examples are presented to validate this method

The Development of a Closed-form Expression for the Input Impedance of Power-return Plane Structures

In multilayer printed circuit boards, the noise on the power bus is influenced by the impedance between the power and ground planes. Power-bus noise estimates require an accurate estimate of the power-bus input impedance. This paper develops a closed-form estimate of the input impedance for circular power-return plane structures. When the structure is lossy (e.g., boards employing embedded capacitance or densely populated boards), the energy reflected from the board edge does not significantly affect the input impedance. In general, the expressions developed here for circular structures can be used to estimate the impedance of lossy power-return plane structures of any shape

Estimating the Power Bus Impedance of Printed Circuit Boards with Embedded Capacitance

Embedded capacitance is an alternative to discrete decoupling capacitors and is achieved by enhancing the natural capacitance between closely spaced power and return planes. This paper employs a simple cavity model to investigate the features affecting the power bus impedance of printed circuit boards with embedded capacitance