Unidirectional error detection, localization and correction for DRAMs: Application to on-line DRAM repair strategies

A novel family of codes for the detection, localization and correction of unidirectional errors for DRAMs in proposed. For DRAM memories, multi-bit soft and hard errors are a growing concern, as the cell sizes continue to decrease with aggressive scaling down. As a result, the classical error detection/correction codes become less efficient to deal with multiple errors in a single word [16]. Berger codes are effective in detecting 100% of the unidirectional errors, but introduce considerable delay and does not provide any error correction feature. In order to decrease the computing time of the code check bits and, at the same time, to provide the possibility to localize the segment(s) where single or multiple errors have occurred, a modification of the Berger code is proposed, called Carry Save K Berger code (CS-K Berger). Basically consists in using Carry Save representations of the partial additions of the word segments. The number of check bits increases as compared with Berger code and consequently the code redundancy overhead increases but the delay in computing the check bits and the corresponding checking is drastically reduced. In addition, some patterns of unidirectional errors become correctable. The proposed CS-K Berger codes for different values of K are analyzed for different word lengths. The hardware required for code generation and verification is discussed as well, as the possibility of using this code for word segment replacement in online applications of DRAMs.