Semiconductor memory device and test method therefor
View Patent ↗Disclosed is a semiconductor memory device, in which the refresh period of a fail cell or cells is set so as to be shorter than that of the normal cells, comprises a control circuit for exercising control in such a manner that, if, when refreshing the cell of a first address, generated responsive to a refresh command, with an input control signal being of a first value, a second address, differing as to the value of a predetermined bit from the first address, is determined to correspond to a fail cell, based on the information ore-programmed in a refresh redundant ROM, the cell of the second address is refreshed, and also in such a manner that, if, with the input control signal of a second value, the second address, differing as to the value of a predetermined bit from the first address, is determined to correspond to a fail cell, based on the predetermined information, only the cell of the second address is refreshed, without refreshing the cell of the first address, generated responsive to the refresh command.
1. A semiconductor memory device including a plurality of cells in need of refreshing for data retention, in which the refresh period for a fail cell with regard to refreshing is made shorter than the refresh period for normal cells, and in which, if, in refreshing a cell of a first address, generated responsive to a refresh command, a second address, different from said first address as to the value of a predetermined bit, is determined, based on the pre-programmed information, as corresponding to a fail cell, the cell of said second address is refreshed, said semiconductor memory device further comprising
a control circuit for exercising control so that, if the second address, different from said first address generated responsive to a refresh command as to the value of a predetermined bit, is determined, based on said pre-programmed information, as corresponding to a fail cell, the cell of said second address only is refreshed without refreshing the cell of the first address.
2. The semiconductor memory device according to claim 1 , wherein said control circuit, receiving a control signal, exercises control so that,
if the control signal is of a first value, and if, in refreshing a cell of a first address, generated from a refresh address generating circuit, a second address, different from said first address as to the value of a predetermined bit, is determined, based on the pre-programmed information, as corresponding to a fail cell, the cell of said second address is refreshed as well; and
if the control signal is of a second value, and if a second address, different from said first address generated by said refresh address generating circuit as to the value of a predetermined bit, is determined, based on the pre-programmed information, as corresponding to a fail cell, the cell of said second address only is refreshed without refreshing the cell of the first address.
3. The semiconductor memory device according to claim 1 , wherein said control circuit, receiving a control signal, exercises control so that,
if the control signal is of a first value, and if, in refreshing a cell of a first address, generated from a refresh address generating circuit, a second address, different from said first address by a predetermined value, is determined, based on the pre-programmed information, as corresponding to a fail cell, the cell of said second address is refreshed as well; and
if the control signal is of a second value, and if a second address, different from said first address by a predetermined value, is determined, based on the pre-programmed information, as corresponding to a fail cell, the cell of said second address only is refreshed without refreshing the cell of the first address.
4. The semiconductor memory device according to claim 2 , wherein said first and second addresses differ from each other as to the most significant bit in a counter generating the refresh address.