[SI-LIST] Re: One stitching via or more vias is better for 25Gbps application???

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: "leeritchey@xxxxxxxxxxxxx" <leeritchey@xxxxxxxxxxxxx>, Leeyuyun <lee.home.61@xxxxxxxxx>
  • Date: Sun, 07 Sep 2014 20:57:39 -0700

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------------------------------------------------------------------
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> >>
> >> --
> >> Steve Weir
> >> IPBLOX, LLC
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> -- 
> 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.
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-- 
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV  89523-9998
www.ipblox.com

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