[SI-LIST] Re: DDR3 routing Topology selection

  • From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
  • To: Vinod Kumar <vinod.kumar@xxxxxxxxxxxx>
  • Date: Wed, 19 Jun 2013 13:10:39 +0200

Hello Vinod,

my comment was not that I would be concerned regarding this overshoots,
it was just that it looks different than what was mentioned in the text.
Solving this via Drive strength setting is the right way to do.

Regarding the Write leveling:
Does it hurt you when the calibration are executed? it might take some
short time at powerup, but if you are not critical on this one I would
leave it in.
Otherwise you have to do quite some measurements to figure out the best
settings e. g. for PVT variations (not really T, and maybe not V, but
Process is considered by the calibration routines).
I had concerns in the beginning when these routines have been
introduced, but in the meantime they are really robust.
So if there is nor specific reason (like Power up time) I would utilize
this feature in any hardware ..

Hermann

Am 19.06.2013 12:03, schrieb Vinod Kumar:
> Hi Hermann,
>
> The overshoot/undershoot problem for T-routing is solved by changing the
> drive impedance on controller side.
> I am working along with Sonu on this and the data given by Sonu was for 34
> Ohm driving impedance. For 40Ohm driving impedance, the voltage swing is
> well within 0V to 1.5V.
>
> Now question is whether the efforts required for DDR3 calibration/write
> leveling for Fly By topology are worth its SI value for a two chip DDR3
> solution. We are still pondering on it.
>
> Regards,
> Vinod
>
> -----Original Message-----
> From: Hermann Ruckerbauer [mailto:Hermann.Ruckerbauer@xxxxxxxxxxxxx] 
> Sent: Wednesday, June 19, 2013 3:03 PM
> To: doltbird1972@xxxxxxxxxxx
> Cc: sonu.goyal@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx; 'Vinod Kumar'
> Subject: Re: [SI-LIST] Re: DDR3 routing Topology selection
>
> Hello,
>
> for two devices at 533 you might have a chance to work without CA
> Termination for the T-Branch.
> For Flyby this might not be possible.
>
> Regarding your comments it looks T is having higher overshoots and therefore
> I would excpect FlyBy to show better SI (what is different than what you
> write).
> T seems to have overshoots, while the levels for FlyBy seems nicly
> terminated and therefore not even reaching the full swing voltage rails ..
>
> Best regards
>
> Hermann
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.EyeKnowHow.de
> Hermann.Ruckerbauer@xxxxxxxxxxxxx
> Itzlinger Strasse 21a
> 94469 Deggendorf
> Tel.: +49 (0)991 / 29 69 29 05
> Mobile:       +49 (0)176  / 787 787 77
> Fax:  +49 (0)3212 / 121 9008
>
> schrieb Doltbird1972:
>> Sonu,
>> As for 2 DDR3 chips on your board, it does not matter what kind of 
>> topology you are using. Just thinking about convenience for your layout.
>> ( The thing will be totally different when more than 4 chips. )
>>
>> Regards!
>>
>> ShaoPeng
>> IEEE Member, Senior SI Consultant and PCB Engineer
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx 
>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Sonu Goyal
>> Sent: 2013年6月19日 16:34
>> To: si-list@xxxxxxxxxxxxx
>> Cc: Vinod Kumar
>> Subject: [SI-LIST] DDR3 routing Topology selection
>>
>> 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
>>
>>
>>
>> ------------------------------------------------------------------
>> 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:
>> http://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:     
>>              http://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:
>> http://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:     
>>              http://www.freelists.org/archives/si-list
>>  
>> Old (prior to June 6, 2001) list archives are viewable at:
>>              http://www.qsl.net/wb6tpu
>>   
>>


-- 

EKH - EyeKnowHow
Hermann Ruckerbauer
www.EyeKnowHow.de
Hermann.Ruckerbauer@xxxxxxxxxxxxx
Itzlinger Strasse 21a
94469 Deggendorf
Tel.:   +49 (0)991 / 29 69 29 05
Mobile: +49 (0)176  / 787 787 77
Fax:    +49 (0)3212 / 121 9008

------------------------------------------------------------------
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:
http://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:     
                http://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: