A Ramp Converter Approach to Rank Modulation

Rank modulation is a new data representation method, which can be used for flash memory devices and other types of nonvolatile memory devices. This innovative technology does not use absolute values of cell levels, but instead uses relations in a group of memory elements. However, to establish rank modulation memory as a practical memory device, efficient and reliable rank determination (read circuitry) must be designed, and the characteristics of the rank modulation memory have to be explored with extensive research and experimental tests. This brief presents a rank modulation memory device, which was fabricated in a 0.35- μm CMOS process. Rank read circuitry with the current-comparing scheme was integrated into the IC, and the rank determination ability was tested. In addition, retention tests were performed to explore how the level changes affect cell ranks in an array of memory cells.