Re: [SI-LIST] : Ferrite Beads

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From: RMELLISON@aol.com
Date: Sat Nov 18 2000 - 12:56:40 PST


Stephen, I agree that you wouldn't want a ferrite in the ground path of a CCA
if you had single ended signals interfacing to other cards through the
backplane. Anytime a single ended signal is referenced to a segmented plane
that is coupled with a ferrite, the return current generates a voltage across
the ferrite. Considering the ferrite in it's most simplistic model, this
would be expressed by e=Ldi/dt+ir. If single ended signals are used across
the backplane, they should be referenced to the ground plane (with no
ferrite) on the CCA, if possible. If there is no control of where they are
referenced in the backplane, tight coupling of the power planes to ground
planes through high frequency caps in the vicinity of the signals lines is
necessary.
Richard Ellison
RMEllison@aol.com

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