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Common Mode Chokes Slide 13

Being able to use inductors and chip beads in place of a common mode choke was covered earlier in this presentation and on this slide is an example where this could hurt users. The inductor or chip bead ferrite will attenuate the noise as well as the signal and not cancel out the noise like the common mode choke would. Würth started at a failure rate of 4.4% at 12MHz and has increased the impedance (as was done previously with a common mode choke) but the resulting failure rate increased to 7.5%. Notice on the 4.4% and 7.5% failure rate chart, the rising peaks of the eye have been distorted. They are not as sharp as they should be, per the 0% failure rate chart below. Two independent filters like two inductors or ferrite beads have no magnetic coupling. This is a result of the chip bead ferrites attenuating both the signal and the noise. Common mode chokes in this case would be the optimum solution, because of the magnetic coupling of both windings.

PTM Published on: 2011-11-11