Patent ID: 7449965

Claim:
A self refresh period signal generation apparatus, comprising: a voltage detection unit for detecting a voltage level of a power supply voltage to generate a plurality of period control signals based on the detected voltage level of the power supply voltage and voltage levels of a plurality of reference voltages; and an oscillation unit for generating a ring oscillation signal having a constant period determined by a resistance of a period control resistor when a self refresh signal is activated, wherein the resistance of the period control resistor is controlled based on logic levels of the plurality of period control signals, wherein the voltage detection unit includes a plurality of voltage comparing units each of which compares the power supply voltage with a corresponding one of the plurality of reference voltages to thereby generate a corresponding one of the plurality of period control signals based on a result of comparing the power supply voltage with the corresponding reference voltage, wherein each of the voltage comparing units includes: a first unit for comparing the power supply voltage with a corresponding reference voltage in order to output the result of comparing the power supply voltage with the corresponding reference voltage; a second unit for selectively transferring an output of the first unit in response to a mode control signal; and a third unit for latching an output of the second unit to output a corresponding period control signal.