Jeff
Ah, you just need to know where to place them. If you happen to be driving
SFP, QSFP, or mid board optic (MBO) modules, you best know what you are doing
if you don't include the right ground vias. I've seen huge jitter and eye
closure over fiber due to this.
Scott
Teraspeed Consulting - A Division of Samtec
Scott McMorrow, Technical Director SI/PI
Office 401-284-1827
www.teraspeed.com | www.samtec.com
-----Original Message-----
From: Loyer, Jeff [mailto:jwloyer@xxxxxxxxxx] ;
Sent: Thursday, December 8, 2016 5:54 PM
To: Scott McMorrow <Scott@xxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: XTalk power flow in differential vias
As Lee said, many designs didn't have the luxury of putting in as many
stitching vias as is typically called for and yet they function fine. If I
insist on more stitching vias than necessary I handicap my designs (more
layers, etc.), so it's important to know how many are required under various
circumstances. For instance, rules should be different for a 200 mil thick
backplane vs. a small 40 mil thick PCB. As I said, I'd still like to have that
examined.
Jeff
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Scott McMorrow
Sent: Thursday, December 08, 2016 10:40 AM
To: dmarc-noreply@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: XTalk power flow in differential vias
When there is no room for stitching vias, then the device itself has a design
problem, and did not account for them in their SI.
Teraspeed Consulting - A Division of Samtec Scott McMorrow, Technical Director
SI/PI Office 401-284-1827 www.teraspeed.com | www.samtec.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Vinu Arumugham
Sent: Thursday, December 8, 2016 1:33 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: XTalk power flow in differential vias
Lee,
"There is no room for "stitching vias'"
There is no free lunch either.
Without stitching vias, interconnect common mode return loss goes up.
Since neither TX nor RX has a perfect common mode termination, common mode
signals will keep reflecting until they are converted into differential or
radiated.
So you pay for it with lower margins or more expensive shielding measures.
Thanks,
Vinu
On 12/07/2016 05:25 PM, heyfitch (Redacted sender heyfitch for DMARC) wrote:
You are free to design your own test board to convince yourself one way or
another. Right?
- VadimÂ
On Wednesday, December 7, 2016, 17:01, leeritchey <leeritchey@xxxxxxxxxxxxx>
wrote:
Cadin, I do design with hundeds of channels densely packed. Â There is no
room for "stitching vias'. Â These all work very well. Â You will find this
the norm with big iron.
Maybe stitching vias are over kill. To use them I would have to be shown that
their effect is significant rather than just visible .
Sent via the Samsung Galaxy S® 6, an AT&T 4G LTE smartphone--------
Original message --------
From: heyfitch <heyfitch@xxxxxxxxx>
Date: 12/06/2016 8:36 PM (GMT-08:00)
To: leeritchey@xxxxxxxxxxxxx, shlepnev@xxxxxxxxxxxxx,
si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: XTalk power flow in differential vias
blockquote, div.yahoo_quoted {margin-left:0 !important;border-left:1px
#715FFA solid !important;padding-left:1ex
!important;background-color:white;}Lee,In fiber optics modules, for
example, the density is so high that diff vias are often right next to
one another. Â The natural inclination is to have as few stitching
vias as possible - to have more routing channels. Â So, 2 stitching
vias per a diff via is typical. Â Yuriy's video clearly shows how the
lower number of stitching vias result into higher insertion loss. Â
This is a trade off consideration, imho. Also, it is desired to have
less than 40dB crosstalk between channels. That is another
consideration. Regards,Vadim Heyfitch
On Monday, December 5, 2016, 13:49, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
wrote:
Why are we worrying about differential vias?
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Yuriy Shlepnev
Sent: Monday, December 5, 2016 11:58 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] XTalk power flow in differential vias
Hello Everyone,
Last Friday I have uploaded visualization of crosstalk power flow in
differential vias - see #2016_13 at
http://www.simberian.com/ScreenCasts.php
 -> How Interconnects Work (higher quality, but may be slow),
YouTube version is available at https://youtu.be/IyuQIl8T_uE The demo ;
video illustrates two ways for the crosstalk reduction. I was really
fascinated with the power flow view of the crosstalk :-) As always, I
will appreciate any feedback.
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, USA Office
+1-702-876-2882; Fax +1-702-482-7903 Cell +1-206-409-2368; Virtual
+1-408-627-7706
Skype: shlepnev
www.simberian.com
Simbeor - Accurate, Productive and Cost-Effective Electromagnetic
Signal Integrity Software
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test
Finalist
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