[SI-LIST] Re: Why is shield grounding necessary for Inpair Skew (Intra pair skew)?
- From: JS <jsven007@xxxxxxxxx>
- To: "weirsi@xxxxxxxxxx" <weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 2 Aug 2013 16:26:27 -0700 (PDT)
Thanks Steve. Capacitance-to-ground (shield) unbalance is major cause of IPS.
Is this because common mode currents require a ground connection? The pair's
shield is present in both cases, just in one cases it is grounded. So if we
measure the pair with shield ungrounded, we just measuring mutual capacitance
unbalance (instead of it and cap-to-ground unbalance)? Anyone with a thorough
explanation much appreciated! Many thanks!
________________________________
From: steve weir <weirsi@xxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Thursday, August 1, 2013 10:57 PM
Subject: [SI-LIST] Re: Why is shield grounding necessary for Inpair Skew (Intra
pair skew)?
In two words: unequal capacitance.
Steve.
On 8/1/2013 6:25 PM, Jus wrote:
> Hi, I am interested in in-pair skew. Hoping another expert could help! :)
> Does anyone know why grounding a differential pair shield (ex. twinaxial or
> twisted pair foil) is needed to generate high within-pair-skew (intra-pair
> skew)? For instance, with the pair's shield grounded the in-pair skew value
> may be 10 ps/ft, while it is only 2 ps/ft with shield ungrounded (shield left
> floating). Why does grounding the shield dramatically increase In-Pair Skew?
> Are there any cases where a differential pair's overall shield or individual
> shield should be left ungrounded when measuring in-pair skew? I think I know
> the answer, hoping for confirmation. Any assistance much appreciated!:)
>
> Jus
>
>
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