[SI-LIST] Re: Why shielded twisted-pair is still twisted?
- From: "Xu, Catherine (ICS)" <xu@xxxxxx>
- To: Neo <neoflash2008@xxxxxxxxx>, List Si <si-list@xxxxxxxxxxxxx>
- Date: Mon, 10 May 2010 22:54:20 +0000
Hi, Neo,
Very interesting question and I am sure you will receive some excellent
feedback from cable experts on the Si-list.
Several factor to consider:
1) shielding reduces electric couple ( xtalk ) due to mutual capacitance, while
twist reduce magnetic coupling due to mutual inductance. Depends on how the
shield was terminated in the system, and what other conductors run inside the
shield, conductors within a shield can still be exposed to mutual inductance
coupling, hence the need for twist.
2) twisted pair is a preferred ( or more balanced ) differential link compare
to coaxial, as the two conductors in a twisted pair are more equal/balanced.
Catherine Xu
__________________________________
Lead HW Design Engineer, Ph.D
HP ICS CHIL - San Diego
__________________________________
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Neo
Sent: Monday, May 10, 2010 3:41 PM
To: List Si
Subject: [SI-LIST] Why shielded twisted-pair is still twisted?
Hi,
I'm thinking about why shielded twisted-pair is still twisted?
Pair is twisted for controlled distance/impedance (due to twist) and for x-talk
reduction. If a pair is already shielded together, it is not necessary to twist
them any more.
Without twist, it will be equivalent to twin-ax cable, isn't that better?
Thanks,Neo
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