The QDRII SRAM has three pairs of clock signals.
Ø K, K#: input clocks
Ø C, C#: output clocks
(Note: C and C# clocks are not offered for QDRII+ devices)
Ø CQ, CQ#: echo clocks: source-synchronous output clocks from the SRAM that accompany read data
The CQ and CQ# clocks are edge-aligned with read data. For high-frequency applications (>=250MHz), CQ and CQ# clocks are preferred for data capture.
The CQ and CQ# clocks and the data output have the same source. The echo clock is source synchronous and edge aligned with the data. So echo clock tracks data better than the K clock.
CQ and CQ# clocks also tracks the data switching noise better than the K clock. This results in better data valid window for the data outputs using CQ/CQ# clocks compared to K clocks.
