[sdiy] semi-OT: USB cable shield

[Ingo Debus]

Hi all,

as far as I know, the shield of USB connectors usually is connected directly to ground. However I've seen designs where there's a smallish capacitor (10 nF) in parallel with an 1 megohm resistor between the housing of the USB receptacle and ground. Why is this? I understand this is done for MIDI connectors to break up ground loops (see? it's not completely OT), same for Ethernet, but USB? USB connectors have a ground pin anyway, so it seems pointless to me to break the ground shield connection for low frequencies while there's still a direct ground connection via the pin.

Any Ideas?

Ingo