Self refresh operation of semiconductor memory device
A method for driving a semiconductor memory device, includes initializing first data corresponding to a refresh time of each corresponding row included in a cell array; storing second data corresponding to column data included in the first row after entering a self refresh mode; setting the first data corresponding to the first row by detecting the refresh time of the first row while performing refresh operations on the other rows in the cell array according to a refresh period selected based on the corresponding first data for predetermined refresh cycles, wherein the refresh operation is not performed on the first row during the predetermined refresh cycles; restoring the second data to the first row; and repeating the above steps for the other rows to thereby set the corresponding first data until the setting step is completed for all rows or the self refresh mode expires.
1. In a semiconductor memory device having a plurality of banks, each said bank including an array of rows and columns, said rows each having a row register unit including a row register corresponding to each said row, and said columns each having a column register unit including a column register corresponding to each said column, a method for determining a refresh time for each said row comprising:
determining if a set refresh period signal is inactive;
if said set refresh period signal is inactive, performing a refresh operation for a row only when a “0” is stored in the corresponding row register of the row register unit.
2. The method defined in claim 1 wherein said corresponding row register is stored with a “1” when column data stored in a predetermined row are the same as data stored in said column register unit and said corresponding row register is stored with a “0” when said column data stored in a predetermined row are not the same as data stored in said column register unit.