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