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VOH(AC) vs VOH(DC) DDR3 measurements

Question asked by mik.nazaryan on Dec 17, 2012
Latest reply on Jan 2, 2013 by algoss
Hi All,
Currently I have a project with DDR3 running at 800 MHz, and DDR3 test application sometimes surprises me with bugs. So I decided to do some measurements manually. I read  the "measurement algorithm" for VOH (AC) and VOH (DC) from Agilent DDR3 Compliance Test instructions. Measurement algorithm VOH (AC) and VOH (DC) are the same ! ? Can't find any difference !!! 
Thus, the question arises. If the measurements algorithms are the same, so why the specification is different?

Here is the Measurement Algorithm for VOH(AC) and VOH(DC).

1 Acquire and split read and write burst of the acquired signal.
2 Take the first valid READ burst found.
3 Find all valid positive pulses. A valid positive pulse starts at VREF crossing at valid rising edge and ends at VREF crossing at the following valid falling edge.
4 Zoom in on the first valid positive pulse and perform VTOP measurement. Take the VTOP measurement result as VOH(AC) value.
5 Continue the previous step with the rest of the valid positive pulses that were found in the burst.
6 Determine the worst result from the set of VOH(AC) measured.


So how separate VOH(AC) and VOH(DC)? 


Edited by: Mik.Nazaryan on Dec 17, 2012 2:49 AM