An inductor device or filter such as an electromagnetic interference (EMI)
filter which includes an inductor provides cancellation of parasitic
capacitance of the inductor and extends high frequency performance of the
inductor or filter by providing the inductor using split windings and
including capacitors to couple signals corresponding to those which are
passed by the equivalent parallel capacitance of the inductor to another
split winding or an inductor in the ground return path. Cancellation of
parasitic capacitance is provided for differential mode and common mode
split windings where the split windings may be either inductively coupled
or not. Forming the split windings as a bifilar winding to increase
coupling coefficient further improves performance and allows cancellation
(as distinct from parasitic capacitance reduction) and avoidance of
resonance in circuits in which an inductor is not permitted in the ground
return path.