A 30- mu A data-retention pseudostatic RAM with virtually static RAM mode

摘要

A 1-Mb (128K*8) pseudostatic RAM (PSRAM) is described. A novel feature of the RAM is the inclusion of a virtually static RAM (VSRAM) mode, while being fully compatible with a standard PSRAM. The RAM changes into the VSRAM mode when the RFSH pin is grounded, even in active cycles. The RAM can be used either as a fast PSRAM of 36-ns access time or as a convenient VSRAM of 66-ns access time. The typical operation current and data-retention current are 30 mA at 160-ns cycle time and 30 mu A, respectively. In order to achieve high-speed operation, low data-retention current, and high reliability, the RAM uses delay-time tunable design, a current-mirror timer, hot-carrier resistant circuits, and an optimized arbiter. These technologies are applicable to general advanced VLSIs.