US Patent 7091816 Common-mode choke coil

A common-mode choke coil comprises an insulating layer and first and second coil conductors. The first and second coil conductors are laminated with the insulating layer interposed therebetween and are magnetically coupled to each other. A width W (mm) and a length L (mm) of at least one coil conductor in the first and second coil conductors satisfy the relational expression of:√{square root over (L/W)}<(7.6651−fc)/0.1385where fc (MHz) is the cutoff frequency with respect to differential-mode noise.