Fundamental EMI source mechanisms leading to common-mode radiation from printed circuit boards with attached cables are presented in this paper. Two primary EMI source mechanisms have been identified: one associated with a differential-mode voltage and another associated with a differential-mode current, both of which result in a common-mode current on an attached cable. These mechanisms can he used to relate printed circuit layout geometries to EMI sources. The two mechanisms are demonstrated through numerical and experimental results, and an example from a production printed-circuit design is presented.

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Investigation of fundamental EMI source mechanisms driving common-mode radiation from printed circuit boards with attached cables

This paper reviews the fundamentals and latest progress of modeling, analysis, and design technologies for signal integrity and electromagnetic compatibility on PCB and package in the past decades. Most results in this field are based on the very rich and highly educational literature produced by Prof. C. Paul in his long scientific career. The inclusion of parameters variability effects is also considered, and it is demonstrated how statistical simulations can become affordable by means of recently-introduced stochastic methods. Finally, the necessity of practical training of designers is mentioned, and an experience relying on realistic PCB demonstrators is illustrated.

Overview of Signal Integrity and EMC Design Technologies on PCB: Fundamentals and Latest Progress

Noise on a dc power-bus that results from device switching, as well as other potential mechanisms, is a primary source of many signal integrity (SI) and electromagnetic interference (EMI) problems. Surface mount technology (SMT) decoupling capacitors are commonly used to mitigate this power-bus noise. A critical design issue associated with this common practice in high-speed digital designs is placement of the capacitors with respect to the integrated circuits (ICs). Local decoupling, namely, placing SMT capacitors in proximity to ICs, is investigated in this study. Multilayer PCB designs that employ entire layers or area fills for power and ground in a parallel plate structure are considered. The results demonstrate that local decoupling can provide high-frequency benefits for certain PCB geometries through mutual inductive coupling between closely spaced vias. The associated magnetic flux linkage is between the power and ground layers. Numerical modeling using an integral equation formulation with circuit extraction is used to quantify the local decoupling phenomenon. Local decoupling can effectively reduce high-frequency power-bus noise, though placing capacitors adjacent to ICs may limit routing flexibility, and tradeoffs need to be made based on design requirements. Design curves are generated as a function of power-bus layer thickness and SMT capacitor/IC spacing using the modeling approach to quantify the power-bus noise reduction for decoupling capacitors located adjacent to devices. Measurement data is provided to corroborate the modeling approach.

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Quantifying SMT decoupling capacitor placement in dc power-bus design for multilayer PCBs

Spread spectrum is a technique introduced for mitigating electromagnetic interference (EMI) problems in many class of circuits. In this paper, with particular emphasis on switching DC/DC converters, we consider the most common and most efficient known spreading techniques, looking for spreading parameters that ensure the highest EMI reduction and the lowest performance reduction in the circuit where the spreading is applied. The result is an interesting tradeoff not only between EMI reduction and performance drop, but also on the EMI reduction itself when considering different EMI victim models. The proposed analysis is supported by measurements on two switching DC/DC converters: 1) based on pulse-width modulation and 2) based on the resonant converter class.

EMI Reduction via Spread Spectrum in DC/DC Converters: State of the Art, Optimization, and Tradeoffs

Influence of the partitioning and bridging of the power/ground planes on the radiation caused by the switching noise on the dc reference planes is investigated both theoretically and experimentally. Based on the three-dimensional finite-difference time-domain modeling, the electromagnetic interference (EMI) performance of the partitioned power/ground planes is studied. Radiated emission at the 3-m distance from the tested boards is measured in a fully anechoic chamber. The measured and the numerical results agree generally well. The radiation behavior of four kinds of partitioned configuration of the power/ground planes is studied. It is found that completely isolating the noise source by the etched slits, or moats, significantly reduces the radiation level at the frequencies near resonance. However, bridges connecting two sides of the moat not only significantly degrade the ability of the EMI protection of the moat, but also excite a new low-frequency resonant mode. The effect of the geometrical parameters, such as the moat size, moat location, bridge width, and bridge position, on the radiation behavior of the printed circuit board is considered. The radiation mechanism of the EMI behavior of the partitioned dc reference planes is discussed.

Numerical and experimental investigation of radiation caused by the switching noise on the partitioned DC reference planes of high speed digital PCB

Parasitic inductance in printed circuit board (PCB) geometries can detrimentally impact the electromagnetic interference (EMI) performance and signal integrity of high-speed digital designs. This paper identifies and quantifies the parameters that affect the inductance of some typical PCB geometries. Closed-form expressions are provided for estimating the inductances of simple trace and ground plane configurations.

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Quantifying EMI resulting from finite-impedance reference planes

The effectiveness of DC power bus decoupling is impacted by the inductance associated with interconnect vias in printed circuit boards (PCBs). Adequate characterization of these interconnects is necessary to facilitate modeling and simulation, and to assess the effectiveness of added decoupling. A measurement procedure is presented for determining the series inductance and resistance of an interconnect with a network analyzer. The validity and limitations of the procedure are discussed. Experimental results of interconnect parameters on an 8/spl times/10 in ten-layer test-board corroborate those measured with a precision impedance analyzer. The measured interconnect values are used to simulate several cases of power-bus decoupling which show good agreement with two-port swept frequency measurements.

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An experimental procedure for characterizing interconnects to the DC power bus on a multilayer printed circuit board

This paper examines the measured power bus impedance of fully populated 4-layer printed circuit boards with internal power and ground planes. Three boards provided by two leading computer companies were evaluated. Each of the state-of-the-art high-speed boards used in this study employed surface-mount decoupling capacitors to reduce noise on the power bus. The boards were measured with and without some or all of their decoupling capacitance. The effectiveness of the decoupling capacitors as a function of location and frequency and the relationship between board impedance and power bus noise was explored. The behavior of 4-layer boards is shown to be quite different than that of boards without planes or boards with closely spaced planes.

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An experimental investigation of 4-layer printed circuit board decoupling

A procedure for diagnosing and modeling radiation from printed circuit boards with attached cables is presented through a case study of a production model electronic control unit. Procedures for determining EMI antennas, IC sources, and mechanisms by which noise is coupled from the IC source to the antenna are suggested.

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Fei Sha

Papers

Investigation of fundamental EMI source mechanisms driving common-mode radiation from printed circuit boards with attached cables

Quantifying EMI resulting from finite-impedance reference planes

An experimental procedure for characterizing interconnects to the DC power bus on a multilayer printed circuit board

An experimental investigation of 4-layer printed circuit board decoupling

Diagnosing and modeling common-mode radiation from printed circuit boards with attached cables