SEMICONDUCTOR STORAGE DEVICE

PROBLEM TO BE SOLVED: To reduce the current consumption without periodical change of self- refresh and without performing this self-refresh operation more than necessary, by combining ring oscillators which become high and low in oscillation frequency respectively by drop of external power source voltage and generating a constant oscillation frequency even when the external power supply voltage drops. SOLUTION: In a ring oscillator configuration of only an inverter 1 connected via P and N type transistors Tr3 and Tr4 to an external power source Vcc and a ground G, when the external power source Vcc is low, the oscillation frequency is high, and when the former is high, the latter is low. And, in the case of a ring oscillator configuration of only an inverter 2 connected with its power source and ground potential supply part direct to the power source Vcc and the ground G, when the external power source Vcc is low, the oscillation frequency is low, and when the former is high, the latter is high. Consequently, if both configurations are combined, and when an output of the inverter 2 is inputted to the inverter 1, the oscillation frequency is almost constant against a change of the external power source Vcc, thus reducing dependency on the external power source.