[SI-LIST] Re: Reference for DDR3 signals
- From: Luping Liu <liewluping@xxxxxxxxx>
- To: razeen_rulez@xxxxxxxxxxx
- Date: Thu, 8 May 2014 18:33:12 +0800
Hi Syed:
For short answer, I suggest you take all the signals reference to
GND, if not enough layers , you can put Add/cmd reference to VDDQ, but keep
the DQ/DM refer to GND. Below are some information about this topic.
1. The latest paper on this work is 'Mixed-Reference for Optimal Cost &
Performance in High-Speed Memory Interface' ,Seunghyun Hwang etc.,
Nvidia,Designcon 2014. It compares the mixed power/ground reference with
all ground reference case, the former may add more crosstalk and
non-negligible power noise coupling to trace. Some may suggest that
sandwich like power/ground reference may have less SSN noise, consider
both 0-1 and 1-0 switch, but I haven't seen any simulation or measurement
data to support this .
2. In my opinion, it is not just a reference plane chose problem ,but a
stackup design or a system design problem, if your design is not cost
sensitive , then chose all ground reference, if cost is make sense, then
we should think both the reference plane and the power integrity problem,
which means ,you can use mixed reference ,but don't forget the power/ground
pair need of the IO power, especially at your high data rate. the G S S P
G like stackup may better than the G S G S P type with careful dielectric
thickness design.
3.Besides the DIMM board reference plane check, both the controller and the
memory chip package reference plane should be checked as a design input
too.
Hope these can helpful to you.
Good luck.
LIU Luping
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