Data Valid Window Calculation

Question: How do you calculate the Data Valid Window in QDRII SRAMs?

 

Answer:

Data Valid Calculation mentioned below is when echo clocks(CQ, CQ#) are used for read capture.

 

The formula for calculating data valid window is tCQHCQ#H -tCQD+tCQDOH.

The switching parameters are defined below:

 

tCQHCQ#H - CQ clock rise to CQ clock rise  (rising edge to rising edge) [This parameter is extrapolated from the input timing parameters (tCYC/2 - 250 ps, where 250 ps is the internal jitter). It is only guaranteed by design and is not tested in production.]    

tCQD - Echo clock high to data valid

tCQDOH - Echo clock high to data invalid

For eg: Data Valid WIndow for the 65nm part CY7C1511KV18 at 300MHz, DVW = 1.4-0.27-0.27=0.86ns

 

Also the tKHK#H parameter calculation differs for 90nm and 65nm parts and the formula is different as indicated in their respective datasheets.