US Patent 7808834 Incremental memory refresh

A memory system comprises charge storage cells and a refresh control module. The charge storage cells have a charge level decay that is based on lifetime erase operations performed on the charge storage cells. The refresh control module increases charge levels of the charge storage cells to offset the charge level decay without first erasing the charge storage cells. A method of controlling a memory system comprises determining charge level decay of charge storage cells having charge level decay characteristics that are based on lifetime erase operations performed on the charge storage cells; and increasing charge levels of the charge storage cells to offset the charge level decay without first erasing the charge storage cells.