| 摘要 |
A multilayer printed wiring board prevents unnecessary emission of electromagnetic waves. The board includes at least two signal wiring layers, at least one ground layer, at least one power source layer, and a ground plane. The board further includes ground wiring adjacent to signal wiring in a signal wiring layer farther apart from said ground layer, the ground wiring being in the signal wiring layer. The ground wiring serves as a return current path for a signal current flowing in the signal wiring. In this structure, the return current path is reserved adjacent to the signal current path and the signal wiring is lower in impedance than the ground plane. The current can be fed back through a shorter closed loop. It is therefore possible to form a small loop to pass a signal current returning to a ground point and flowing through each signal wiring arranged in the board and a return current of the signal current. This minimizes unnecessary emission of electromagnetic waves. It is also possible to form a small loop to pass a signal current returning to a ground point and flowing through each signal wiring in at least two different layers connected via a through-hole to each other and a return current of the signal current.
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