Electric power consumption reduction device

A semiconductor device for selecting and using as the power voltage thereof a first power voltage and a second power voltage of an absolute value less than that of said first power voltage, comprising:

• a voltage generation circuit for generating said first power voltage, said second power voltage, and a constant voltage of a potential intermediate between those of said first power voltage and said second power voltage;
• and
• first and second gate circuits mutually connected by signal transmission paths and each capable of operating equally well under said first power voltage and said second power voltage;
• wherein
• during a switching of power voltage to said first and second gate circuits from said first power voltage to said second power voltage or from said second power voltage to said first power voltage, a stepwise switching of power voltage is performed by generating the constant voltage of intermediate potential before switching to said first or second power voltage.

A microcomputer comprising:

• a clock output circuit for outputting a first clock and a second clock of a frequency lower than that of said first clock;
• a central processing unit (CPU) operating by using either of said first and second clocks output by said clock output circuit;
• a voltage generation circuit for generating a first power voltage, a second power voltage of an absolute value less than that of said first power voltage, and a constant voltage of a potential intermediate between those of said first power voltage and said second power voltage;
• and
• a control circuit for controlling operation of said voltage generation circuit;
• wherein:
• said control circuit controls operation of said voltage generation circuit in such a manner that stepwise switching of a power voltage occurs such that, when said CPU is operating using said first clock, said first power voltage is generated from said voltage generation circuit;
• when said CPU is operating using said second clock, said second power voltage is generated from said voltage generation circuit;
• and when switching between said first power voltage and said second power voltage is being performed, said constant voltage of intermediate potential is first generated before switching to said first or second power voltage.

A microcomputer comprising:

• a clock output circuit provided with a first oscillation circuit for generating a first clock, a second oscillation circuit for generating a second clock of a frequency lower than that of said first clock, and a clock selection circuit for selecting and outputting said first or second clock on the reception of a clock select signal;
• a central processing unit (CPU) operating by using said first or second clock output by said clock output circuit;
• a voltage generation circuit for generating a first power voltage for operations using said first clock, a second power voltage of an absolute value less than that of said first power voltage for operations using said second clock, and a constant voltage of a potential intermediate between those of said first power voltage and said second power voltage;
• and
• a control circuit for providing control such that, on receiving an instruction from said CPU indicating that clock-switching is to be performed, said control circuit generates a control signal for said voltage generation circuit and said clock select signal, and causes stepwise switching of said power voltage and clock switching by applying said signals to said voltage generation circuit and said clock selection circuit, respectively.

An electric equipment including a microcomputer, comprising:

• a clock output circuit for outputting a first clock and a second clock of a frequency lower than that of the first clock;
• a central processing unit (CPU) operating by using either of the first and second clocks output by the clock output circuit;
• a voltage generation circuit for generating a first power voltage, a second power voltage of an absolute value less than that of the first power voltage, and a constant voltage of a potential intermediate between those of the first power voltage and the second power voltage;
• and
• a control circuit for controlling operation of the voltage generation circuit, wherein;
• the control circuit controls operation of the voltage generation circuit in such a manner that stepwise switching of a power voltage occurs such that, when the CPU is operating using the first clock, the first power voltage is generated from the voltage generation circuit;
• when the CPU is operating using the second clock, the second power voltage is generated from the voltage generation circuit;
• and when switching between the first power voltage and the second power voltage is being performed, the constant voltage of intermediate potential is first generated before switching to the first or second power voltage.