[SI-LIST] Re: Via modeling shows strange behavior
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 29 Feb 2012 10:46:02 -0800
Vinu,
You actually answered your question - the ground via in your case does not
connect anything. Current goes from one side of the plane to another and
does not require any additional connections. The ground via probably adds
some capacitance to the signal via barrel and make the via discontinuity
worse (more reflection comparing to the case without the "ground" via).
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, USA
Office +1-702-876-2882
Cell +1-206-409-2368
Skype: shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Vinu Arumugham
Sent: Wednesday, February 29, 2012 10:00 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Via modeling shows strange behavior
1. Since the layer 2 ground is common to Top and layer 3, a ground via seems
unnecessary.
2. With no ground via, the stub portion of the via will have higher
impedance - which is good.
So perhaps the ground via is degrading performance by decreasing the
impedance of the via stub?
Thanks,
Vinu
On 02/29/2012 09:19 AM, Ravinder.Ajmani@xxxxxxxxxxxxxx wrote:
> Hi Experts,
> I am doing via modeling using Cadence PCB SI GXL. I have a 6-layer
> stackup, and via is connecting the interconnect from Top layer to
> Layer 3, with Layer 2 as Ground. I modeled the via with a single
> Ground via placed at the closest distance the tool will allow, and
> then modeled the same via without the Ground via. The Insertion Loss
> and the Return Loss for the Single via are about 15 - 20% better then
> the Ground coupled via. I am puzzled with the results. I will
> appreciate if you can help me understand the reason for this.
>
> Thanks.
>
> Regards,
> Ravinder Ajmani
> Server PCB Development
> Hitachi Global Storage Technologies
>
>
> Email: Ravinder.Ajmani@xxxxxxxxxxxxxx
>
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