Bus architecture for 600-MHz 4.5-Mb DDR SRAM

A double data rate (DDR) SRAM bus architecture which can eliminate any speed penalty for doubling the I/O frequency and support single data rate (SDR) compatibility has been proposed. A method to guarantee data coherency for both DDR and SDR has also been described. With this architecture, we developed a 4.5 Mb DDR SRAM. Under the typical 2.5 V condition, a 600 MHz I/O frequency was achieved.