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What are the DLL on DDR memories used for?

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buenos

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hi

as far as i knew, in DDR-1 memory systems, only the memory controller has a DLL circuit (delay-locked-loop), but the memory chips dont have. so during writes the data and strobe have 90deg phase difference on the board traces, during reads, they have 0deg (controller makes the 90deg delay on the incoming strobe signals).

i heard, the DDR-3 memories have DLL in the memory chips. what are those used for? does the memory actually provides the 90deg strobe delay?

i have to design a board with DDR3, so it would be good to know.
 

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dll ddr

Also DDR2 chips have a DLL to retime read DQ and DQS, as you can see from the datasheets.
 

buenos

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why dll is used in ddr

hi

thanx.
how does it retime? during read, or write?
does it do the 90deg delay, or what?
 

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ddr dll design

During read, consult the datasheets.
 

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