Architecture difference between QDR-II and QDR SRAM

Question: What is architecture difference between QDR-II and QDR SRAM?

 

Answer:

The major differences are

1. DLL is available in the QDR"-II (No DLL present in QDR").

2. Extra half cycle of latency on the QDR"-II (2 cycle latency on the QDR" while the QDR"-II has a 2.5 cycle latency).

3. Extended data valid window on the QDR"-II (1.7ns data valid window @ 166MHz for QDR" while on the QDR"-II has a 2.2ns data valid window.)

4. Cannot operate QDR"-II across varying frequency ranges if DLL is turned on. (E.g. 250MHz device can only operate between 120Mhz and 250Mhz.) QDR on the other hand can operate from 0MHz to 250MHz for a 250MHz device.