DDR3 questions.

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I just ran into this site last Friday and want to thank you for all the information. This is a big help to me.

In your course you cover DDR3 but do you cover the different configurations? Point to point vs T? And when and where to use termination resisters in each of those configurations? Decoupling? And VTT and Vref when to use what?

One last question.. Silly really.. I read on this site where there was a jedec reference design for DDR3 and a link to it. but I can’t seem to find it now that its Monday:)

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Hello Ron,

I am very happy you found it useful. In our Advanced PCB Layout course I explain how to route iMX6 Rex DDR3 (Data – point to point, Address/Command/Control – T branch topology). I do also explain things about Fly-by topology, but I do not go into details about termination and VTT as these are not part of the iMX6 Rex design.

Didn’t you find the DDR3 JEDEC reference design examples at my blog? Have a look at: http://www.fedevel.com/welldoneblog/2011/02/ddr-ddr2-ddr3-pcb-layout-examples/

Hope it helps,

Robert

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Thanks for the reply,

I will be signing up shortly.

I am a PCB/IC layout designer. I have never worked with DDR3 so it’s all new. I am not an engineer but have been in electronics for 20+ as a CAD person.

So.. Why would one use Vtt or not use Vtt? I also noticed other things about the layout. 1 is the decoupling caps are near but not routed to pins on the ddr rams. is this normal? I know its working for your design. and yeah.. no or few termination resistors(you do terminate the clocks). is this due to the accumulation of resistors on the ram chips+ routing making termination unnecessary? please explain to a total noob.

Thanks agian.

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VTT should be used, but it may not be required for some designs (e.g. short tracks, low frequency, …). I always recommend to check design guide for the particular chip and memory configuration – they will tell you if termination resistors are required. Decoupling: the memory chips are from both sides, there is no other way to place decoupling capacitors, but same technique is used also in memory modules – tested and works oki. Hope it helps. Robert

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