Tsuyoshi Maeno

Split width effect of ground patterns on FM-band cross-talks between two parallel signal traces of printed circuit boards

Electromagnetic disturbances in vehicle-mounted radios are mainly caused by conducted noise currents flowing through wiring-harnesses from vehicle-mounted printed circuit boards (PCBs) with common slitted ground patterns. To investigate suppression of these kinds of noise currents, previous measurements from simple two-layer PCBs with two parallel signal traces with slitted and non-slitted ground patterns, and revealed that making slits with open ends on the ground patterns in parallel with the traces can reduce the conducted noise currents. It was also discovered that the noise currents from PCBs can be suppressed even if the size of the return ground is small. Furthermore, we performed finite-difference time-domain (FDTD) simulations, using eight simple two-layer PCB models in which the ground patterns were split into two parts with different widths and one PCB model with a plane ground pattern, and found that cross-talk decreases with widening the width of the ground pattern and has the smallest values at a specific width. In the present study, to confirm the above findings experimentally, we made actual PCB samples according to exactly the same specification as the models used in the FDTD simulation, and measured the cross-talk between the two parallel signal traces with respect to the different widths of ground patterns. The results approximately agreed with the simulation.

Effect of ground layer patterns with slits in suppressing cross-talks between two parallel signal traces on printed circuit board

For electromagnetic (EM) disturbances in vehicle-mounted radios, the main source is known to be conducted noise currents flowing through wiring-harnesses from vehicle-mounted multi-layer printed circuit boards (PCBs). To investigate a design method that can suppress the conducted noise currents, we previously measured noise current outflows from four types of simple three-layer PCBs having two perpendicular signal traces and different ground patterns with/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 two slits ground types are smaller compared to the case for the asymmetric two slits ground types. In the present study, to further confirm the above finding, we fabricated six types of simple two-layer PCBs having two parallel signal traces and different ground patterns with/without slits, and measured the cross-talks between the traces to evaluate the noise current outflows from the PCBs. As a result, we found that the ground pattern with the slits perpendicular to the traces cause noise current outflows larger by 19-42 dB at 100 MHz than the ground pattern with no slits, while the ground patterns with the slits in parallel with the traces can provide current noise levels slightly smaller by 2.5-5 dB compared to the case for the no-slit ground pattern. These results were confirmed by the FDTD simulation, and were also qualitatively explained from an equivalent circuit model we previously proposed.

Slit Effect of Ground Patterns on Conducted Noise Currents from Printed Circuit Board

Electromagnetic disturbances for vehicle-mounted radios can be caused mainly by conducted noise currents flowing out from vehicle-mounted multi-layer printed circuit boards (PCBs) to wire-harnesses. Using actual electronic equipment for vehicles, we previously showed that combining, not separating, the ground layer patterns of a digital circuit and an analog circuit is more advantageous to reduce the noise current outflow, while the mechanism remains unknown. In the present study, based on an idea that this mechanism should generate from a change in the amount of common return currents flowing to the ground, we measured noise current outflows from five types of simple PCBs having different ground patterns, which were validated from simulation with the method of moment. As a result, we could confirm that slits on a ground pattern allow conducted noise currents to flow out from PCBs, while the levels for the symmetric two slits ground types are smaller compared to the case for the asymmetric two slits ground types. The mechanism could be explained qualitatively from balanced conditions of an equivalent bridge circuit.

Reduction effect of ground patterns on conductive noise currents from printed circuit board

Conductive noise currents flowing out from vehicle-mounted electronic equipment composed of multi-layer printed circuit boards (PCBs) to wire-harnesses form a major disturbance source for vehicle-mounted radios. Using actual vehicle-mounted electronic equipment, we previously showed that, to reduce the noise current outflow of this type, combining, not separating, the ground layer patterns of a digital circuit and an analog circuit is more advantageous, while the mechanism remains unknown. In the present study, based on an idea that this mechanism generates from a change in the amount of common-mode return currents flowing to the ground, we simulated noise current outflows with the method of moment from three types of simple PCBs having different ground patterns, which were validated from measurement of scattering parameters. Furthermore, we could confirm that slits on a ground pattern allow conductive noise currents to flow out from PCBs.