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Correct way to terminate connector shielding

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marko.severin

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Hi guys,
I'm getting a bit confused on how to correctly terminate connector shielding (like USB, D-SUB, or similar). For instance, most of the board I've seen uses the RC variant, like this one:
cap.png

However, Texas Instruments uses a ferrite bead instead in one of their designs (Sitara Starterkit):
ind.png

These are two completley different approaches. One shorts high frequencies to GND, the other blocks them. Which one is correct, or better said, when do I use one and when the other?

Thanks and best regards,
Marko
 

The first one uses capacitors for coupling to a single ground.

The second is using a ferrite bead to isolate the high-frequency noise on the digital ground from getting to the chassis/USB ground while still connecting the two grounds together for DC. That's a common technique to help isolate analog and digital grounds while still allowing them to be tied together at one place for DC or lower frequency AC continuity between grounds.
 

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