1. Field
The present disclosure relates to data transfer.
2. Description of the Related Art
Popular ways of transferring data in applications such as memory accesses are Single Data Rate (SDR), Double Data Rate (DDR) and Quad Data rate (QDR). SDR typically transfers one unit of data per clock cycle. By a unit of data it is meant that data may be sent in parallel on several data lines. For example, a memory device might have eight Input/Output (I/O) lines. Thus, each individual I/O line might transfer one bit of data per clock cycle. The clock being referred to here may be a clock that is shared by a transmitter and a receiver.
For DDR, data may be transferred on both the rising and falling edges of the clock signal. Therefore, DDR may send twice the amount of data as SDR in the same time period.
In QDR, data may be sent at four different points in the clock cycle. For example, data could be sent on a rising edge of the clock, between the rising and a falling edge, the falling edge of the clock, and between the falling edge and the next rising edge. Therefore, QDR may transmit four times the data per clock cycle as SDR.