[SI-LIST] Re: DDR2 design
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>, ivorlist@xxxxxxxxxxx
- Date: Wed, 22 Feb 2006 21:11:33 -0800
Oops, I missed that 100 and 75 ohms at the end. Bad Steve, very bad.
Steve.
At 05:41 PM 2/22/2006, Scott McMorrow wrote:
>ivor
>
>Okay, I think your gut tells you that you have a
>potential problem. I see several issues here:
>
>1) 75 ohms is a bit high for single ended trace
>impedance. This will have a large impact on
>overshoot/undershoot at the receivers, if the
>termination is not well matched. It will also
>have a large impact on crosstalk.
>
>2) Signal quality concerns matter first. You
>haven't told us your application, but from your
>sig, you appear to be designing control system
>processors. Given the liability issues
>involved, you might want to be sure that you
>don't overstress a part and cause it to fail.
>Simulation is only ways to be sure. The
>trial-and-error method only works if you are
>lucky enough to build with worst case fast
>process devices. If you are unlucky, you will
>build your boards with parts that "seem" to
>work, but are not representative of the worst case.
>
>3) Even at DDR2 333, timing closure can be a
>pain, especially with an FPGA. Not only do you
>have issues with signaling ISI, but you also
>have problems with SSO noise from the FPGA, and
>crosstalk jitter in the channel.
>
>Regards,
>
>Scott
>
>
>Scott McMorrow
>Teraspeed Consulting Group LLC
>121 North River Drive
>Narragansett, RI 02882
>(401) 284-1827 Business
>(401) 284-1840 Fax
>
><http://www.teraspeed.com>http://www.teraspeed.com
>
>Teraspeed® is the registered service mark of
>Teraspeed Consulting Group LLC
>
>
>Ivor Bowden wrote:
>>
>>Hi Steve,
>>
>>I really do appreciate your comments. I know I have not done my
>>homework, this was just dropped in my lap. I'm just looking for general
>>comments, I don't expect anyone to run free sims for me. Comments like,
>>"seems reasonable" or "no way" or "star routing might be better", etc.
>>is about all I hoped for. I apologize if my request came off rude.
>>
>>I am open to simulation quotes, I believe it a good idea, if I can get
>>approval.
>>
>>Sincerely,
>>
>>Ivor
>>
>>on 2/22/2006 4:34 PM steve weir wrote:
>>
>>>
>>>Ivor, maybe. Nothing sounds terribly wrong, but that is really
>>>inadequate. You need to simulate, or get someone else to simulate for
>>>you. Then you can see if any adjustments are needed and make them. You
>>>need to account for what the silicon is up to as well as the trace.
>>>
>>>With all due respect your question comes off a bit like: "Guys, I
>>>haven't done my homework, would someone do it for me?" If someone is so
>>>willing, great. I would be surprised to see that. I would also suspect
>>>the answer.
>>>
>>>If you want detailed free help, your best chance is from your chip
>>>suppliers. Maybe Altera will run the simulation for you.
>>>
>>>Steve.
>>>At 03:22 PM 2/22/2006, Ivor Bowden wrote:
>>>
>>>>
>>>>Hi SI Experts,
>>>>
>>>>I am reviewing a layout for an embedded DDR2 design using 4 Micron DDR2
>>>>chips with an Altera Cyclone controller. The memory is set up to be 64
>>>>bits wide, 16 bits per chip.
>>>>
>>>>The target rate is 167MHz. The design is not simulated.
>>>>
>>>>Termination is as follows:
>>>>ODT may be supported, still investigating.
>>>>There is no series term.
>>>>There is 0.9V stub term for control lines.
>>>>There is a differential 100 ohm term for each clock pair (4 total).
>>>>
>>>>Routing is as follows:
>>>>Control lines are daisy chained and length matched between the first
>>>>DRAM and controller (about 1"), each DRAM (about .75") and the last DRAM
>>>>and terminators (about .25"); total net length is about 3.5".
>>>>Data lines are length matched at about 3" (controller to DRAM).
>>>>Clock lines are length matched at about 4" (controller to DRAM).
>>>>Trace impedance is targeted at 100 ohms for clock and control lines, and
>>>>75 ohms for data lines.
>>>>
>>>>Is this design likely to work? If not, what changes should be considered?
>>>>
>>>>I very much appreciate all comments. Thank you!
>>>>
>>>>Ivor Bowden
>>>>Engineer
>>>>Curtiss-Wright Controls
>>>>
>>>>------------------------------------------------------------------
>>>>To unsubscribe from si-list:
>>>><mailto:si-list-request@xxxxxxxxxxxxx>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>//www.freelists.org/webpage/si-list
>>>>
>>>>For help:
>>>><mailto:si-list-request@xxxxxxxxxxxxx>si-list-request@xxxxxxxxxxxxx
>>>>with 'help' in the Subject field
>>>>
>>>>List FAQ wiki page is located at:
>>>>
>>>><http://si-list.org/wiki/wiki.pl?Si-List_FAQ>http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>>>>
>>>>List technical documents are available at:
>>>> <http://www.si-list.org>http://www.si-list.org
>>>>
>>>>List archives are viewable at:
>>>>
>>>><//www.freelists.org/archives/si-list>//www.freelists.org/archives/si-list
>>>>or at our remote archives:
>>>>
>>>><http://groups.yahoo.com/group/si-list/messages>http://groups.yahoo.com/group/si-list/messages
>>>>Old (prior to June 6, 2001) list archives are viewable at:
>>>> <http://www.qsl.net/wb6tpu>http://www.qsl.net/wb6tpu
>>>>
>>>>
>>>
>>>
>>>
>>>
>>
>>
>>------------------------------------------------------------------
>>To unsubscribe from si-list:
>><mailto:si-list-request@xxxxxxxxxxxxx>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>//www.freelists.org/webpage/si-list
>>
>>For help:
>><mailto:si-list-request@xxxxxxxxxxxxx>si-list-request@xxxxxxxxxxxxx
>>with 'help' in the Subject field
>>
>>List FAQ wiki page is located at:
>>
>><http://si-list.org/wiki/wiki.pl?Si-List_FAQ>http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>>
>>List technical documents are available at:
>> <http://www.si-list.org>http://www.si-list.org
>>
>>List archives are viewable at:
>>
>><//www.freelists.org/archives/si-list>//www.freelists.org/archives/si-list
>>or at our remote archives:
>>
>><http://groups.yahoo.com/group/si-list/messages>http://groups.yahoo.com/group/si-list/messages
>>Old (prior to June 6, 2001) list archives are viewable at:
>> <http://www.qsl.net/wb6tpu>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 FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
