On the Electromagnetic Radiation of Printed-Circuit-Board Interconnections (original) (raw)
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A simple method to model a printed circuit board (PCB) that takes advantage of the unique features found in PCBs is proposed. This method is capable of analyzing coupling between any nets in the entire multilayer PCB. Using the equivalence principle, the PCB is modeled as a cascade of parallel-plate waveguides with half-space regions residing above and below the PCB. Instead of formulating the problem in terms of electric currents in the horizontal metal layers, it is formulated using equivalent magnetic currents in the nonmetallic regions of layer interfaces. The equivalent magnetic currents at the dielectric interfaces are expressed in terms of the Rao-Wilton-Glisson (RWG) basis functions. The electric currents flowing on the vias inside dielectric layers are assumed constant in the vertical direction. These vertical electric currents radiate TEM modes in the parallel-plate environment. Integral equations based on simple parallel-plate and free-space Green's functions enforcing the boundary conditions are set up and solved using the method of moments (MoM). The equivalent magnetic currents in each layer interact with currents in the adjacent layers only, thereby resulting in a "chained-block-banded" matrix. Excitation is provided through ports defined at each pair of pads, or between a pad and nearby ground. These ports are located only on the top and the bottom layers of the PCB where the circuit components and integrated-circuit pins are mounted. Two different localized excitation schemes, one with a current loop injection and the other with a strip current excitation, are proposed. This formulation requires the computation of the MoM matrix only once per frequency for any number of ports. Further, the solution for only those unknown equivalent magnetic currents around the port regions is required to obtain the -port impedance parameter characterization of the PCB. Consequently, a memory-efficient block matrix solution process can be used to solve problems of large size for a given memory. Simple and realistic examples are given to illustrate the applicability of this approach.
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The differential-mode signals in printed circuit board (PCB) traces are unlikely to produce significant amounts of radiated emissions directly; however these signals may induce commonmode currents on attached cables, enclosures, or heat sinks that result in radiated electromagnetic (EM) interference. Full-wave EM modeling can be performed in order to determine the level of radiated emissions produced by a PCB, but this modeling is computationally demanding and does not provide the physical insight necessary to explain how differential signals induce commonmode currents on distant objects. This paper describes a model for determining the common-mode currents on cables attached to a PCB that is based on the concept of imbalance difference. The imbalance difference model is derived from research that shows that changes in geometrical imbalance cause differentialto common-mode conversion. This paper applies an imbalance difference model to PCB structures and compares the resulting equivalent source configurations to those obtained with traditional voltage-and current-driven models, as well as full-structure simulations.
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An electronic product has to comply with a myriad of EMC requirements before it can be marketed globally. Radiated Emission is one of the EMC requirements which constantly poses a challenge to many circuit designer due to the ever increasing speed of PCB clocks. Consequently, in the product it is essential to investigate, identify, model and predict the PCB radiated emission before compliance test is performed for cost and time saving. In this paper, a simple double layer PCB board is fabricated to investigate the PCB radiated emission. Three PCB configurations are investigated for the level of emissions and to correlate with the common-mode currents. These configurations are PCB without attached cables, with one attached cable and with two attached cables. The radiated emission from each configuration is measured in a semi-anechoic chamber at open circuit and 50 ohm loads. It can be shown that the cables are the major sources of radiated emission due to the common-mode currents flowing through it.
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This paper presents a novel modeling approach for predicting the response of a printed circuit board (PCB) trace excited by a nonuniform electromagnetic (EM) radiated field from complex electronic components. The proposed approach is analytic and it is based on transmission line model with distributed sources taking into account the effect of the effective relative permittivity ε reff of the PCB surrounding medium. The modeling procedure is a two-step approach: three-dimensional radiated emission modeling of the electronic component, source of EM disturbance, and using a set of equivalent sources followed by the computation of the induced voltages in the trace terminals referring to analytic coupling formulations. Comparison between modeled, numerical, and measured results enables us to validate the proposed model. Index Terms-Coupling formulations, electromagnetic interferences (EMIs), near-field measurement, printed circuit board (PCB) traces, three-dimensional radiated emission.
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