Sergiu Radu

An investigation of PCB radiated emissions from simultaneous switching noise

Processors are currently operating with fundamental clock frequencies that are at or above the resonant frequencies of typical processor boards and modules. Adequately decoupling printed-circuit boards (PCBs) at high frequencies has become an increasingly urgent task in the light of increasing clock frequencies with decreasing rise times. Providing sufficient charge at frequencies near and above 1 GHz is extremely difficult with lumped-element capacitors. To further complicate the issue, modern PCB power buses may be analogous to microstrip-patch antennas. Exciting a power bus at board harmonics may result in significant radiated EMI from the bus. Much has been done to improve high-frequency decoupling from a signal-integrity perspective. However, the benefit to EMI is somewhat unclear, because the mechanism by which power-bus noise results in radiated EMI is not well understood. Input impedance of a power bus, transfer impedance across a power bus, and radiated emissions from a PCB are presented herein. The results are discussed to provide characterization of radiated EMI directly from a PCB power bus.

The EMI benefits of ground plane stitching in multi-layer power bus stacks

The effect on EMI of stitching multiple ground planes together along the periphery of multi-layer PCB stacks is studied. Power bus noise induced EMI and radiation from the board edges is the major concern herein. The EMI at 3 meters for different via stitch spacing and layer thickness is modeled with FDTD modeling. It is shown that the ground plane stitching effectively reduces the radiated EMI that results from fringing fields at the power bus edges. Two families of curves are generated to demonstrate the variation of the radiated EMI as a function of layer thickness and stitch spacing. Further studies show that the reduction of the EMI from ground plane stitching may be compromised by other radiation mechanisms.

An investigation of the effects of PCB module orientation on radiated EMI

Electronic equipment is frequently designed with modular construction to more efficiently use available real-estate, as well as provide for expansion capability and interchangeability. Perpendicular and parallel module configurations are both reasonably common, although perpendicular modules are becoming more prevalent with the standardization of the PCI bus in the computing industry. Modular designs may behave as EMI antennas if excited by a common-mode noise source. Magnetic- and electric-field coupling mechanisms have previously been documented that may excite the EMI antenna at the module bus-connector or on the module. The antenna and transmission-line characteristics of the perpendicular and parallel modules were investigated numerically and experimentally. A case study of a commercially available product using the parallel-module configuration is provided to show the relevance of modules as EMI antennas.

Signal induced EMI in fibre channel cable-connector assemblies

The EMI performance of cable-connector assemblies designed for FC-0 transmission has been studied. Two types of cable and two connector styles were evaluated. Experimental results show that the dominant radiation mechanism for short cable lengths is the common-mode current caused by source and PCB skew that leaks to the exterior of the shield via the transfer impedance of the connector. However, the cable imbalance becomes a more significant source of common-mode current than the source skew when the cable assembly is tens of meters long.