Semiconductor device with electromagnetic radiation reduced

A semiconductor device in which power is supplied from an external power supply system, comprising:

• an input terminal;
• an output terminal;
• a first power supply system connected to first terminals of power supply and ground and a digital inner circuit, wherein said inner circuit includes a clock signal generating circuit, a driver for the clock signal, and circuits operating in response to the clock signal;
• and
• a second power supply system connected to second terminals of power supply and ground, said input terminal, said output terminal, and a digital interface circuit, wherein said second power supply system is independent of said first power supply system, and wherein said interface circuit includes a MOS transistor for pulling up or down said input terminal and an output circuit which includes a MOS transistor driving said output terminal,
• wherein said first power supply system is separated from said second power supply system, and said inner circuit is connected to said interface circuit through only signal lines.