In addition to paper you sent, below is one study with asymmetric differential pairs. ( most large bga breakouts wont have symmetric diff pairs) http://www.univ-brest.fr/SPI/pages/Slides/SPI_2009_S7_1.pdf Its not the exact same case of transition via's but still. > On Sep 8, 2014, at 4:54 AM, Bert Simonovich <bertsimonovich@xxxxxxxxxx> wrote: > > Here is a DesignCon2013 paper on the effect of nearby gnd via placement on HS > SE and Diff Signals by: > A. Jaze; B. Archambeault; and S. Connor. > > http://e.ubmelectronics.com/images/DesignCon2014/12-WA2_Paper_EffectofNearbyGroundVia.pdf > > Bert Simonovich > > >> On Sep 8, 2014, at 3:35 AM, Leeyuyun <lee.home.61@xxxxxxxxx> wrote: >> >> Hi, Steve >> Could you help explain >>> I think that you are considering a high frequency problem in low >>> frequency terms >> I do not understand "in low frequency terms", could you help clarify it? >> How to roughly evaluate cavity effect when stitching via close to signal >> vias? >> Any white paper or material to show stitching via effect? >> When I ask two parties to run two kinds of simulation, including only one >> stitching vias and more stitching vias, the result from two parties is >> different. One shows only one stitching is better, but another shows more >> stitching vias better. How do I make decision which one is correct? >> Thank you >> Lee >> >>> steve weir <weirsi@xxxxxxxxxx> 於 2014/9/8 上午11:57 寫道: >>> >>> It is neither. It is a description of the physics. Real engineering >>> accounts for pertinent physics. >>> >>> Best Regards, >>> >>> >>> Steve >>>> On 9/7/2014 6:41 PM, leeritchey@xxxxxxxxxxxxx wrote: >>>> This sounds like a bit of supposiition rather than real engineering. >>>> >>>> Sent from my HTC One™ X, an AT&T 4G LTE smartphone >>>> >>>> ----- Reply message ----- >>>> From: "steve weir" <weirsi@xxxxxxxxxx> >>>> To: "Leeyuyun" <lee.home.61@xxxxxxxxx> >>>> Cc: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx> >>>> Subject: [SI-LIST] Re: One stitching via or more vias is better for 25Gbps >>>> application??? >>>> Date: Sun, Sep 7, 2014 10:43 AM >>>> >>>> >>>> I think that you are considering a high frequency problem in low >>>> frequency terms. Stitch vias impact the cavity, and when they are in >>>> close proximity to signal vias and traces, they affect wave modes near >>>> those structures. Thinking about stitch vias and the cavities that they >>>> traverse as though they are continuations of the TEM path that breaks at >>>> a Z axis transition is not a good approximation. The Z axis signal >>>> transition injects the signal energy into the cavity. The various >>>> properties of the cavity: material, and geometry, including what vias >>>> stitch the cavity surfaces together and where affects how that signal >>>> energy propagates through the cavity in all directions. >>>> >>>> Steve >>>>> On 9/7/2014 5:31 AM, Leeyuyun wrote: >>>>> Hi, Steve >>>>> But IL and RL should depend upon the distance / via pad size of signal >>>>> via and gnd stitching via >>>>> If only depend on capacitor vsd via, is the return path loop larger to >>>>> create large inductance? >>>>> Does it fit into 25Gbps application? >>>>> Could you advise what is the benefit of case 1 and case 2? >>>>> Thanks >>>>> Lee >>>>> >>>>> >>>>>> steve weir <weirsi@xxxxxxxxxx> 於 2014/9/7 下午6:11 寫道: >>>>>> >>>>>> The statement is based on the idea that Vss stitching from bypass >>>>>> capacitor Vss vias and IC Vss vias is adequate. The idea concludes that >>>>>> explicit vias corresponding to signal or signal pair transitions are not >>>>>> necessary. >>>>>> >>>>>> Steve >>>>>>> On 9/7/2014 2:46 AM, Leeyuyun wrote: >>>>>>> Stitching should be needed when gnd reference plane change >>>>>>> I do not know why you said do not need any stitching vias >>>>>>> I want to clarify my question as below >>>>>>> # means stitching vias, * means signal vias, + means positive signal, - >>>>>>> means negative signal >>>>>>> 1. Only on stitching vias >>>>>>> +++++++++++++++++*++++++++++ >>>>>>> # >>>>>>> --------------------------*---------------- >>>>>>> 2. At least two stitching vias >>>>>>> # >>>>>>> ++++++++++++++++*+++++++++++ >>>>>>> >>>>>>> ------------------------*------------------ >>>>>>> # >>>>>>> For each structure, what is theory behind? What is your recommendation >>>>>>> for stitching via structure in the 25Gbps structure? >>>>>>> >>>>>>>> "Lee " <leeritchey@xxxxxxxxxxxxx> 於 2014/9/7 上午3:17 寫道: >>>>>>>> >>>>>>>> No stitching vias are needed. Where did this idea get started? >>>>>>>> >>>>>>>> -----Original Message----- From: Leeyuyun >>>>>>>> Sent: Saturday, September 06, 2014 4:25 AM >>>>>>>> To: si-list@xxxxxxxxxxxxx >>>>>>>> Cc: lee.home.61@xxxxxxxxx >>>>>>>> Subject: [SI-LIST] One stitching via or more vias is better for 25Gbps >>>>>>>> application??? >>>>>>>> >>>>>>>> Hi, all >>>>>>>> I am doing 100Gbps (4x25Gps) product now >>>>>>>> How do we put stitching vias when high speed signal change the layer? >>>>>>>> This is a differential pair, which has P and N >>>>>>>> Someone told me that one stitching vias is better because P and N >>>>>>>> share the common return >>>>>>>> Someone told me that more stitching vias is better because loop >>>>>>>> inductance could be reduced more >>>>>>>> I am confused which one is better? >>>>>>>> Can anyone help me? >>>>>>>> Thanks, >>>>>>>> Lee------------------------------------------------------------------ >>>>>>>> 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 forum is accessible at: >>>>>>>> http://tech.groups.yahoo.com/group/si-list >>>>>>>> >>>>>>>> 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 >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> ----- >>>>>>>> No virus found in this message. >>>>>>>> Checked by AVG - www.avg.com >>>>>>>> Version: 2014.0.4765 / Virus Database: 4015/8162 - Release Date: >>>>>>>> 09/05/14 >>>>>>> ------------------------------------------------------------------ >>>>>>> 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 forum is accessible at: >>>>>>> http://tech.groups.yahoo.com/group/si-list >>>>>>> >>>>>>> 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 >>>>>> 1580 Grand Point Way >>>>>> MS 34689 >>>>>> Reno, NV 89523-9998 >>>>>> www.ipblox.com >>>>>> >>>>>> (775) 299-4236 Business >>>>>> (866) 675-4630 Toll-free >>>>>> (707) 780-1951 Fax >>>>>> >>>>>> All contents Copyright (c)2013 IPBLOX, LLC. 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All Rights Reserved. >>>> This e-mail may contain confidential material. >>>> If you are not the intended recipient, please destroy all records >>>> and notify the sender. >>>> >>>> ------------------------------------------------------------------ >>>> 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 forum is accessible at: >>>> http://tech.groups.yahoo.com/group/si-list >>>> >>>> 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 >>> 1580 Grand Point Way >>> MS 34689 >>> Reno, NV 89523-9998 >>> www.ipblox.com >>> >>> (775) 299-4236 Business >>> (866) 675-4630 Toll-free >>> (707) 780-1951 Fax >>> >>> All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved. >>> This e-mail may contain confidential material. >>> If you are not the intended recipient, please destroy all records >>> and notify the sender. >> >> ------------------------------------------------------------------ >> 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 forum is accessible at: >> http://tech.groups.yahoo.com/group/si-list >> >> 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list 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