8-ns CMOS 64 K×4 and 256 K×1 SRAMs

SRAMs (static random-access memory) with a 64 K×4 and 256 K×1 structure and with 8-ns access time have been developed on a 1.0-μm CMOS process. Circuits are designed with source-coupling techniques to achieve high speed with small signal swings, using only CMOS devices. A metal option permits selection of the 64 K×4 or 256 K×1 configuration. The same core architecture has also been used to generate ×8 and ×9 designs. An output-enable (OE) version achieves 3-ns response time. As system speeds have recently increased toward 100-MHz operation, the need for address transition detection (ATD) has diminished as a means for improving the SRAM speed/power ratio. This trend in SRAM design stems mainly from the fact that AC current becomes the most significant fraction of the total current. Accordingly, the design described here employs a purely static path through the entire SRAM, with no requirement of ATD at any point. The resulting DC current is countered with a combined strategy of array subdivision, small-signal techniques, and active preamplification at key points in the data path