US Patent 7667549 Semiconductor device and driving method thereof

A low-power-consumption semiconductor device and a driving method thereof where a clock signal generation is controlled. A transmission and reception control circuit to control signal communication with an outside; a ring oscillator control circuit to detect an edge in a receiving signal and control a ring oscillator; a clock generation circuit to generate a clock signal based on the ring oscillator; and a logic circuit to operate based on a clock signal are included. During signal communication between the transmission and reception control circuit and the outside, the ring oscillator operates and a clock signal is output from the clock generation circuit when the ring oscillator control circuit detects an edge in a receiving signal, and the ring oscillator stops and output of the clock signal from the clock generation circuit stops when transmission of a reply signal from the transmission and reception control circuit to the outside is terminated.