[SI-LIST] Re: VIA stubs
- From: Jory McKinley <jory_mckinley@xxxxxxxxx>
- To: "kngabrie@xxxxxxxxx" <kngabrie@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 20 Aug 2012 08:13:08 -0700 (PDT)
Hello Knut,
The Via stub presents the first resonance at about 33Ghz. Based on your signal
rate assuming sinusoidal all your meaningful energy content will be below 15Ghz
(the majority at 3Ghz) so you should be ok from a reflection standpoint. Your
signal will however experience the added capacitance of the stub slowing the
edge a bit. I would simulate the Via with nearby return and neighbor Via to
check out your assumptions as well as get an idea of how much coupling and
z-direction energy might be hitting the cavities.
-Jory
________________________________
From: Knut Gabrielsen (kngabrie) <kngabrie@xxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Sent: Monday, August 20, 2012 10:57 AM
Subject: [SI-LIST] VIA stubs
Hello Experts!
I am involved in a design where we need to transfer ~6Gbit/s diff-signals
between a processor and an FPGA. If I route these signals as striplines inside
the PCB, there will be a stub on the (through-hole) VIA, stub-length ~1100um =
43mil.
My question to you all: Should I be concerned? At what frequencies will a VIA
stub seriously affect SI?
And - will the signal see the stub itself, or just "experience" the VIA as a
stray capacitance on the transmission line?
Rgds,
Knut
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