Embedded ram with self-test and self-repair with spare rows and columns

Abstract

A self-repair method for a random access memory (RAM) array comprises writing a value to the memory array, reading a value from the memory array and comparing the read and write values to identify faulty memory cells in the memory array. An address of a newly-discovered faulty memory cell is compared to at least one address of at least one previously-discovered faulty memory cell. The address of the newly discovered faulty memory cell is stored if a column or row address of the newly-discovered faulty cell does not match any column or row address, respectively, of a previously-discovered faulty memory cell. Flags are set to indicate that a spare row or a spare column must replace the row or column, respectively, identified by the address of the previously-discovered faulty memory cell, if the row or column address of the newly-discovered memory cell matches the respective row or column address of the previously-discovered faulty memory cell. Spare rows and columns that have been indicated by the flags as requiring replacement are allocated to replace faulty rows and columns respectively. The remaining spare rows and columns whose row and column addresses respectively have been stored are then allocated. Furthermore, the RAM is flagged as unrepairable if an insufficient number of spare rows or spare cells remain to replace all of the rows or columns containing faulty cells.