Patent ID: 7574312

Claim:
A semiconductor device that is configured to operate at any of a plurality of predetermined frequencies, the semiconductor device comprising: a plurality of functional units; a power source network having a plurality of branches that supply power from a power source to said pluraity of functional units; and a plurality of switching units, each of said switching units provided along one of said pluraltiy of branches for switching ON/OFF the supply of power via the associate branch from the power source to said plurality of functional units, wherein said plurality of functional units includes: a storage unit configured to map and store the plurality of predetermined frequencies and pieces of switching information designating on ON state or an OFF state of said switching units, the pieces of switching information being set to provide different impedance values of said power source network; and a control unit configured to read, from said storage unit, a piece of switching information corresponding to a current operating frequency of the semiconductor device, and control the ON/OFF switching of said plurality of switching units in accordance with the read piece of switching information, the pieces of switching information are set so as to keep an impedance value of said power source network within a predetermined range, for any of the plurality of predetermined frequencies at which the semiconductor device operates, said plurality of functional units further includes a frequency detecting unit configured to monitor the current operating frequency and, when the current operating frequency changes, detect a new current operating frequency after the change, and said control unit read from said storage unit a piece of switching information corresponding to the current operating frequency after change as detected by said frequency detecting unit.