| 摘要 |
PURPOSE:To reduce electromagnetic radiation noises in a signal line of a signal layer provided between two conductive layers made up of a power supply layer or a ground layer, by forming a three-dimensional electric closed loop current path with the conductive layer. CONSTITUTION:In a circuit board 2, a three-dimensional closed loop current path for shielding is formed. Especially for the shielding in a high-frequency range, overlapped areas of patterns are increased between layers, through holes are placed nearer to each other, and a line-shaped connection structure is employed in the circuit board 2 so that impedance at a connection part between the layers, which constitute a closed loop current path 8, becomes several OMEGAor less. As for a signal line 4, as a noise source, in a signal layer 3, the signal line 4 is surrounded in a three-dimension way in a four-layer structure, which is made up of an outside ground layer 5, a signal layer 6, the signal layer 3, and a power-supply layer 7 so that the closed loop current path 8 is formed.
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