High speed DDR memory interface design

As the bandwidth requirement increases, Double Data Rate (DDR) interface is becoming very commonly used in many types of memories, such as, DDR I/II/III DRAM, RLDRAM I/II, QDR I/II/II+ SRAM etc. The major feature of DDR interface compared to a single data rate (SDR) one is to use both rising and falling edges of a clock to transfer data which allow it to provide two times the throughput at the same clock frequency.