[SI-LIST] Re: DDR3 routing Topology selection

  • From: Hany Fahmy <hanymhfahmy@xxxxxxxxx>
  • To: sonu.goyal@xxxxxxxxxxxx
  • Date: Wed, 19 Jun 2013 10:40:15 +0200

Hi Sonu. Flyby was developed by JEDEC for clock, address/command and
control signals. We find that T-topo is better for data bus. Check all DIMM
routing that data bus is T-topology. Pls pay attention to short stubs of
the Sdram connection.  Hope this helps.
On Jun 19, 2013 10:35 AM, "Sonu Goyal" <sonu.goyal@xxxxxxxxxxxx> wrote:
> Hi
> We are designing a custom board where 2 DDR3 chips (533MHz) are interfaced
> with processor. There are two routing toplogies which we are considering
> for our layout.
> 1. T topology
> 2. Fly-By topology
>
> We have done pre-layout SI simulation using hyperlynx. As we know  for DDR3
> flyby topology is recommended by JEDEC but according to our simulation
> results  T topology is looking better.
>
> In T topology overshoot is coming 1.6V and undershoot is -0.1V and in
> Fly-By topology overshoot is coming at 1.225V and undershoot at 240mV. I am
> attaching snapshots here. Please confirm what topology flyby or T topology
> we should prefer for our board.
>
> Regards
> Sonu Goyal
>
>
>
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