Low Power embedded DRAM caches using BCH code partitioning

Technology advances have recently enabled the use of DRAMs into logic integrated circuits. These embedded DRAMs can be used to efficiently implement caches since DRAMs require substantially less area than SRAMs. One challenge for DRAM based caches is that a small time between refreshes is needed to ensure data retention. These refreshes increase the power consumption even when the cache is idle. To mitigate this issue, the use of longer times between refreshes combined with the use of Error Correction Codes (ECCs) has been recently proposed. The idea is that the time between refreshes can be increased significantly while only causing data retention failures on a small percentage of the cells. Then those errors can be corrected by the ECC. For this scheme to be efficient the number of additional bits required by the ECC should be small. This is achieved by using large data blocks for the ECC which in turns means that a large data block has to be accessed even when only a small portion of it is needed. This has no effect on idle power consumption but increases the dynamic power consumption and reduces the effective memory bandwidth. In this paper, a technique to mitigate this issue is proposed. It enables better granularity in the read data accesses by partitioning the ECC block into two sub-blocks and modifying the error detection and correction processes. This reduces the dynamic power consumption and increases the available memory bandwidth while requiring only a moderate increase in the number of additional bits.