| 摘要 |
PROBLEM TO BE SOLVED: To reduce a leak amount of current at a sub threshold area of a transistor by making a substrate voltage impressed to the transistor at a self refresh operation of a cell consisting of one transistor and one capacitor lower than that impressed at a refresh operation. SOLUTION: A back bias voltage generator 10 generates a first or second back bias voltage in response to a refresh mode control signal NORM or a self refresh mode control signal SREF and supplies to a DRAM. A first, a second back bias voltage detectors 21, 31 compare the first, second back bias voltages with a first, a second reference voltages set thereinside, and send out an enable signal to the back bias voltage generator 10, thereby holding the back bias voltage at a predetermined value. The second reference voltage is set to be 0.5-0.3 times the first reference voltage. Accordingly, a refresh time cycle is relatively elongated. |
