Patent ID: 7475261

Claim:
A system comprising: a processor chip; a power source monitoring circuit to monitor a voltage level of a power source to supply a supply voltage to the processor chip; a capacitor to hold the supply voltage even when the power source cannot supply voltage higher than a predetermined voltage level; wherein the processor chip comprises a logic circuit; wherein the power source monitoring circuit keeps a control signal in a first state, while the voltage level is below the predetermined voltage level, and wherein the logic circuit is controlled to change an operation mode from a normal operation mode to a standby mode in response to a change of the control signal from a second state to the first state; wherein the processor chip comprises a substrate bias control circuit to control a substrate bias voltage of a transistor of the processor chip so that an absolute value of a threshold voltage of the transistor in the standby mode is higher than the absolute value of the threshold voltage of the transistor in the normal operation mode; wherein the logic circuit is controlled not to change input of the logic circuit in the standby mode, and wherein when the processor chip changes from the standby mode to the normal operation mode, the substrate bias control circuit starts to change the substrate bias voltage of the transistor of the processor chip first and the logic circuit is controlled to change the input of the logic circuit after the substrate bias voltage becomes a predetermined voltage.