SYSTEM

PROBLEM TO BE SOLVED: To provide a system composed of semiconductor devices mounted on a substrate by which no electric power is wasted, noise can be effectively reduced up to high frequencies and power source decoupling for a semiconductor device such as a microcomputer can be achieved. SOLUTION: The system is composed of an LSI package 1, a bypass capacitor 3, a filter 5 and the like which are mounted on the substrate. The filter 5 includes stub wiring 4 (λ/4) which is connected between the bypass capacitor 3 and a backbone power source and is composed of circuits which exhibit an impedance lower than that of the power source path. In this way, when noise is generated from the LSI package 1, the noise current is allowed to flow into the filter 5, is reflected from an open end of the stub wiring 4 and returns. Noise current from the LSI package 1 after λ/2 is canceled at a branch point of the stub wiring 4 by this action. COPYRIGHT: (C)2004,JPO