[SI-LIST] Re: DDR3 Signal Quality & Timing Analysis - Probe Location at DRAM - Pin or Die?
- From: "Pugazharasan Selvanathan - ERS, HCL Tech" <pugazharasan.s@xxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 31 Oct 2011 19:14:58 +0530
Hello Steve,
Thanks for your guidance. Our DDR3 interface do not use DIMM and have all
SDRAMs on the main board itself. On comparing the clock design with "DDR3 SDRAM
Unbuffered DIMM Design Specification 1.03", I found discrepancies in Ccomp and
Rtt values.
Parameter - Current - Recommended
Ccomp - 3.3pF - 2.2pF
Rtt - 49.9ohm - 36ohm
However, the intra-pair length matching is properly done in layout in
accordance with JEDEC specification.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Monday, October 31, 2011 3:55 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: DDR3 Signal Quality & Timing Analysis - Probe Location
at DRAM - Pin or Die?
Did you follow the JEDEC topology recommendations for the CLK?
Steve.
On 10/31/2011 3:13 AM, Pugazharasan Selvanathan - ERS, HCL Tech wrote:
> Hello everyone,
> My observations from the simulation results of a DDR3 interface (64 bit + 8
> bit ECC) with five Micron DRAMs:
>
> In FAST corner, when CLK is probed at PIN of first DRAM in the daisy chain,
> it has good signal quality (monotonic, no DC/Vref multi-crossing). But if it
> is probed at DIE of the same DRAM, CLK is non-monotonic, multi-crosses DC and
> Vref thresholds. Signal Quality improves at die of the other DRAMs as we
> progress down the daisy chain, since the stub length between respective DRAMs
> and termination decreases.
>
> Give your thoughts to improve the signal quality at first DRAM's die.
> Currently, the output impedance of DDR3 Controller is set to 40ohms, which is
> the maximum O/P impedance it supports.
>
> Thanks,
> Pugazharasan Selvanathan
> Member Technical Staff - Design Centric Services
> HCL Technologies Ltd.
> #94, South Phase, Ambatur Industrial Estate, Chennai-600058
> Tel: +91-44-66892000 Extn: (2695)
> www.hcl.com<http://www.hcl.com/>
>
>
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--
Steve Weir
IPBLOX, LLC
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