I am designing a BF547-based system with DDR memory. Is serial termination of DDR lines always required? Is it possible to connect DDR chip directly to BF547 if tracks are short (say, less than 1")?
Peter- you might want to look at the technical notes on Micron's website:
especially TN-46-06 and TN-46-14.
Steven J. Ackerman, Consultant
ACS, Sarasota, Florida
thank you very much. By chance, I've read these application notes today. Now I understand that serial termination is strongly reccomended, as well as careful simulation of PCB layout.
In my application there is a shortage of PCB space. I wonder if there is any positive experience NOT to use termination resistors, provided the PCB contains only one DDR chip and the distance between it and BF547 is very short.
Peter- I guess you could layout and try a prototype board to see if it would work, but I'd be wary of it in production. You would have to utilize some pretty sophisticated test equipment to verify the signal integrity, and, if your code or data is residing in this SDRAM could you tolerate errors ?
In laying out this product:
I found that it was important to utilize both series and parallel termination as well as balance the signal lengths - DDR timing is fairly stringent. As a result of the attention paid to these details up-front there were no problems with the design - it just worked.
it looks like serial termination is a must in all cases. Thanks a lot.
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