FW: [SI-LIST] : Cable Shielding: How do you connect the drains?

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From: Fasig, Jonathan L. (fasig.jonathan@mayo.edu)
Date: Mon Apr 02 2001 - 15:24:42 PDT


Many years ago, Paul Brokaw at Analog Devices published an applications note
entitled
"An IC Amplifier User's Guide to Decoupling, Grounding, and Making Things Go
Right for a Change"
wherein he proposed an approach for dealing with questions of this nature:
Principle: Think-where the currents will flow.

While this paper dealt primarily with IC op amps and their related
applications, I have often found Paul's advice to be applicable to a variety
of situations including the one you raised regarding shield drains. Many
times one can anticipate problems by considering how currents might flow if
a particular connection is made and contrasting that with a review of where
those currents will flow if that same connection is not made. Each system
is unique and the analysis can become involved but in general the approach
is usually helpful.

If you have time you might look over the original text at

http://www.analogdevices.com/techsupt/application_notes/AN-202.pdf
<http://www.analogdevices.com/techsupt/application_notes/AN-202.pdf>

Hope this helps.

jf

-----Original Message-----
From: Stacy_L_Gore@raytheon.com [mailto:Stacy_L_Gore@raytheon.com]
Sent: Monday, April 02, 2001 8:47 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : Cable Shielding: How do you connect the drains?

If you are running differential signals between to racks through a shielded
cable, what should you do with the cable drains?

* Hard wire both-ends to the chassis?

* Hard wire one end and let the other float?

* Float both ends?

* Connect through a series resistor, or series cap, or series cap and
resistor in parallel?
Is there a rule of thumb or formula based on something to help you determine
how to connect the shielding?
I have seen it done several different ways but never have been real sure
which way is correct.

Thanks,
Stacy

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