Slit Effect of Common Ground Patterns in Affecting Crosstalk Noise between Two Parallel Signal Traces on Printed Circuit Boards

It is well known that electromagnetic (EM) disturbances in vehicle-mounted radios are mainly caused by conducted noise currents flowing through wiring harnesses from vehicle-mounted printed circuit boards (PCBs) having common ground patterns with slits. To evaluate the noise current outflows from PCBs of this kind, we previously measured noise current outflows from four types of simple three-layer PCBs having two perpendicular signal traces and different ground patterns with or without slits, and showed that slits on a ground pattern allow conducted noise currents to flow out from PCBs, while the levels for the symmetric slit ground type are smaller than in the case of two asymmetric slit ground types. In the present study, to further investigate the above finding, we fabricated six types of simple two-layer PCBs having two parallel signal traces and different ground patterns with and without slits, and measured the crosstalk noise between the traces. We found that the ground patterns with the slits perpendicular to the traces increased the crosstalk noise levels, which were 19 to 42 dB larger than those for the ground pattern with no slits, while the ground patterns with the slits parallel to the traces were able to reduce the noise levels, which were slightly smaller (by 2.5 to 4.5 dB) than in the case of the no-slit ground pattern. These results were confirmed by FDTD simulation, and were also qualitatively explained by means of an equivalent bridge circuit model that we previously proposed. (C) 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(10): 19-24, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10287