[SI-LIST] Re: Problems of using DDR SDRAM with out VTT termination?
- From: "Ferhat Yaldiz" <ferhat.yaldiz@xxxxxxxxxxxxxx>
- To: "'icer world'" <icermail@xxxxxxxxx>, "'SI LIST'" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 3 Apr 2009 11:14:30 +0300
Hi,
As you said, functions of VTT are reduce reflection and better SI.
Generally, JEDEC standarts for PC industries and PC mainboards have many
DIMMs. If you have two or more DIMMs, you will have more stubs and these
stubs will result more problems.(in terms of signal quality (glitch,
ringing, reflections ...) and timing) But if you dont have not more
stubs,more component or more DIMMS,you do not have to use VTT.
But, you must simulate your topologies with VTT and without VTT.
Regards,
FERHAT YALDIZ
HARDWARE DESIGN ENG.
TUBITAK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of icer world
Sent: Friday, April 03, 2009 4:49 AM
To: SI LIST
Cc: liujb@xxxxxxxxxx
Subject: [SI-LIST] Re: Problems of using DDR SDRAM with out VTT termination?
What is the function of VTT? From the JEDEC Standard ,the VTT is to reduce
the reflection and improve the signal integrity.
In my opinion,when DDR controller connects many DDRs chips by data pin,not
by CS pin,It is unnecessary to use the VVT to reduce the reflection.
Can anyone give me some suggestion,thanks?
________________________________
From: Terrance Kao (tekao) <tekao@xxxxxxxxx>
To: Jaison Fernandez <jaisonf@xxxxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
Sent: Friday, April 3, 2009 8:03:20 AM
Subject: [SI-LIST] Re: Problems of using DDR SDRAM with out VTT termination?
Jaison,
I used to have problem with Infineon DDR without termination.
Infineon IO driver was weak.
Without terminating to VTT, it failed to meet the DDR timing.
While Samsung and Micron didn't have this issue.
But as die kept shrinking, there is no guarantee that Samsung, Micron,
or other vendor won't have the same issue.
You need to check with the memory vendors.
Regards,
Terry
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Jaison Fernandez
Sent: Wednesday, April 01, 2009 10:25 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Problems of using DDR SDRAM with out VTT termination?
Dear All,
Going through some of the NEC and NXP SoC's reference schematics shows
that the VTT supply for DDR is not used.
Can we use DDR SDRAM with out VTT termination?
If we use DDR with out VTT termination what can be the possible problems
expected from the Board? (In terms of SI and EMC)?
What are the system design considerations taken to mitigate above
problems?
With Warm Regards,
JAISON FERNANDEZ
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