US Patent 7742355 Dynamic random access memory with low-power refresh

A technique to reduce refresh power in a DRAM. In one embodiment, all of the DRAM memory cells are refreshed at a first rate and a subset of the memory cells are refreshed a second rate greater than the first rate. In another embodiment, the DRAM has a refresh controller that generates a refresh address and controls the refresh of the memory cells addressed by the refresh address. A marker memory is used by the refresh controller to determine which of the memory cells requires refreshing at a rate faster than the refresh rate of the remaining memory cells. Testing the DRAM uses a method to determine which of the memory cells are to be refreshed at the faster rate and to store the results in the marker memory.