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- mu m 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.<
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