ELECTROMAGNETIC INTERFERENCE SUPPRESSING DEVICE AND ELECTROMAGNETIC INTERFERENCE SUPPRESSING CIRCUIT

PROBLEM TO BE SOLVED: To suppress electromagnetic noise while stabilizing power supply and reducing man-hour for design. SOLUTION: A wiring layer 4 and a ground layer 6 are laminated alternately through an insulation layer 8. An odd wiring layer 4, counting from the lowest one, is connected with a just above wiring layer 4 through a via hole 10 at a right end and an even wiring layer 4 is connected with a just above wiring layer 4 at a left end. The lowermost wiring layer 4 is connected with a signal terminal 14 and the uppermost wiring layer 4 is connected with a signal terminal 16 and each ground layer 6 is connected with a ground terminal 18 at a side on the ground terminal 18 side. Power supply terminal of an LSI is connected with the signal terminal 14, for example, and a capacitor is connected between the signal terminal 16 and a capacitor thus constituting an electromagnetic interference suppressing circuit. Since an electromagnetic interference suppressing device 2 forms an equivalent transmission line and has characteristic impedance matched with the equivalent series resistance of the capacitor, reflection is reduced significantly. Consequently, a high frequency power supply current from the power supply terminal of an LSI is bypassed effectively to the electromagnetic interference suppressing device 2.