Abstract: A miniaturized common mode EMI filter with a greatly simplified design so that it can be manufactured very economically. The common mode filter includes: (a) a magnetic main body; (b) a pair of substantially identical electrically conductive planar coils embedded in the magnetic main body; and (c) an insulative planar coil sandwiched between the pair of electrically conductive planar coils, wherein the insulative planar coil has a pattern that is substantially identical to and inclusive of the pattern of the electrically conductive planar coils so as to insulate the pair of electrically conductive planar coil from each other. The common mode filter retains low normal mode impedance and high common mode impedance, with a substantially reduced physical size, so that it can cost-effectively maintain a high fidelity of the normal mode waveform of signals for electronic devices that utilize differential transmission technology and keep the common mode EMI noise to a minimum.