[SI-LIST] Re: DDR-Length matching
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- Date: Thu, 28 Apr 2011 09:30:59 -0700
Jeff, thanks. I just ask that people be very careful distinguishing
requirements from guidelines and recommendations. It's a huge waste of
a design and verification teams' time if in their product circumstances
they have to do something extraordinary to get 4ps of end to end skew
when 20ps will do just fine because a well-intentioned guideline is
misinterpreted as a performance specification.
Steve.
On 4/28/2011 9:15 AM, Loyer, Jeff wrote:
> My apologies - I should not have used the word 'spec'. I was referring to
> what are often called 'Design Guidelines'.
>
> For most accurate reading, replace 'spec.' w/ 'guideline'. I think the terms
> 'specify' and 'specified' are ok.
>
> Jeff Loyer
>
>
> -----Original Message-----
> From: steve weir [mailto:weirsi@xxxxxxxxxx]
> Sent: Thursday, April 28, 2011 9:00 AM
> To: Loyer, Jeff
> Cc: karthi keyan; si-list@xxxxxxxxxxxxx
> Subject: Re: [SI-LIST] Re: DDR-Length matching
>
> For all you guys that sit on these committees, I recommend calling these
> unnecessarily tight matches "Guidelines" and "Best Practices", and
> restricting specifications to actual performance requirements. This
> avoids building assumptions about tools and practices into
> specifications, without losing the benefit of practical experience in
> the guidelines.
>
> Steve.
>
> n 4/28/2011 8:25 AM, Loyer, Jeff wrote:
>> +/-10 mils tolerance means that all signals in that group must be within 20
>> mils of each other.
>> If your longest trace is 6.253", and your shortest is 6.234", you have met
>> the spec.
>> If your longest trace is 6.253", and your shortest is 6.232", you fail the
>> spec.
>>
>> The spec. could call out '+/-10 mils' or 'within 20 mils', with the same
>> meaning.
>>
>> The '+/- 10 mils' verbiage is usually used to align with popular layout
>> tools' conventions, where you specify +/- xx mils of a defined target.
>> Finding that target is part of the process for your particular design.
>>
>> When they specify this kind of tolerance, they usually also insist on
>> routing on the same layer, so propagation velocity differences don't come
>> into play.
>>
>> This tight a tolerance (within 20 mils, or about 3-4ps) is usually specified
>> because experience has proven that it doesn't take CAD folks much longer to
>> meet a +/- 10 mil spec. than a +/- 100 mil spec., and we can reduce the skew
>> from routing to essentially zero.
>>
>> Jeff Loyer
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>> Behalf Of karthi keyan
>> Sent: Thursday, April 28, 2011 2:42 AM
>> To: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] DDR-Length matching
>>
>> Hi experts,
>> I am working on boards having DDR interface. on layout we are
>> following the below groupings& length matching
>>
>>
>> Group1- Data signals,strobe,Mask with in group +/-10 mils tolerance
>> Group2- Add/Ctrl/Cmd/Clk--with in group +/-10mils tolerance
>>
>> i am clear on groupings but on length matching i want to know how
>> to calculate the exact Min& max length matching tolerance .
>>
>> can you please let me clear on DDR length matching?
>>
>>
>> Thanks,
>> Karthikeyan
>>
>>
>> ------------------------------------------------------------------
>> 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 technical documents are available at:
>> http://www.si-list.net
>>
>> 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 technical documents are available at:
>> http://www.si-list.net
>>
>> 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
>>
>>
>>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
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:
