[SI-LIST] Re: DDR3-1600 Double-Tee Topology
- From: "Liu, Bowen" <bowen.liu@xxxxxxxxx>
- To: "goswamisurjendra@xxxxxxxxx" <goswamisurjendra@xxxxxxxxx>, "Moran, Brian P" <brian.p.moran@xxxxxxxxx>
- Date: Tue, 14 Jan 2014 18:08:43 +0000
Joseph,
It depends on whether you are designing a system with SDP (single die package)
or DDP (dual die package) DRAM devices. If it is SDP, it doesn't matter which
topology you use, both daisy-chain and double-T topologies should work fine for
you, but if you are using DDP device, then double-T topology works better than
daisy-chain in term of giving better system margin. Even though daisy-chain
topology (common for DDR3) can distribute load effect to improve margin, but it
normally can cause some reflections among loads, and it is worse for DDP case.
I believe that's why DDR3/L RC-D (daisy-chain with DDP device) was only
supported up to 1066MTs. Like other people suggested, you can always run some
simulation to verify which topology works better for you when you have doubts
like this.
Thanks,
Bowen
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Surjendra Goswami
Sent: Tuesday, January 14, 2014 9:52 AM
To: Moran, Brian P
Cc: josephaday@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: DDR3-1600 Double-Tee Topology
Joseph,
DDR3 supports write leveling and hence the fly-by topology is the most
prolific an DDR3 designs.
The double tee topology was used for DDR2 and had some downside in the
impedance discontinuities due to branching along the routes causing obvious
margin losses.
Regards
Surjendra
On Tue, Jan 14, 2014 at 10:25 PM, Moran, Brian P <brian.p.moran@xxxxxxxxx>wrote:
> Joseph,
>
> I have seen the Tee-Tee or the hybrid Tee-Daisy topology used in some
> instances. You are correct that the Tee-Tee is a pain to route and
> usually requires a type 4 MB. We do employ it in some LPDDR3 memory
> down configurations. In either case, it does require some impedance
> compensation between the main trunk and the tee branches in order to
> optimize. This is different than the tree topology used in DDR2, in
> that the length to all loads is matched. Where we found the Tee-Tee
> particularly interesting is when using multi-die pkgs. The daisy
> chain topology does not work well with high capacitance loads, such as
> you can have with LPDDR3 DDP and QDP devices. You can get excessive
> ledging and ringback in the first few nodes in the daisy chain. This
> is the reason the Tee-Tee topology was developed. However, if you are
> supporting only SDP devices then the daisy chain is the most
> straightforward.
>
> Brian Moran
> Memory Interface Technology
> Client Platforms
> Intel Corporation
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Joseph Aday
> Sent: Monday, January 13, 2014 6:07 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] DDR3-1600 Double-Tee Topology
>
> Hi Everyone,
>
> Has
> anyone tried using a double-tee topology with their
> address/command/control signals in DDR3L/LPDDR3? This would be
> instead of the standard daisy-chain, with an Rtt at the end of the line.
>
> For example, take a controller with four memory nodes. It would look
> like this (think of DDR2 days):
>
> - RX
> - Branch -|
> | - RX TX ----------------- Rtt
> | - RX
> - Branch-|
> - RX
>
> To ensure matched timing for write leveling, this would even apply to
> the differential clock. I am doing memory-down (chips directly on the
> PWB as opposed to DIMMs.. if that matters?)
>
> Compared
> to a simple daisy chain, my simulations show this to be a bad idea
> both in eye diagram margins and in s-parameter plots. The double tee
> has less vertical / horizontal eye margin. The double-tee also has a
> resonant "suck out" in insertion loss very close to the clock
> frequency, whereas the standard daisy-chain is relatively flat out to 3GHz.
>
> Our
> chip vendor tells us this is needed to improve the eye diagram, but I
> can't see how or why. This is also a pain to route.. and so I have no
> good ideas as to why I should do this :)
>
> Am I missing something? Thoughts? Anyone else in the same boat? :)
>
> Thank you,
> Joseph Aday
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
