Patent ID: 8866566

Claim:
A common mode filter, comprising: a lumped-constant differential delay line of m derived type or all pass type formed by arranging inductors, being passive series elements, and capacitors, being passive parallel elements, in a differential four terminal network composed of the passive series elements arranged in series in each differential line and the passive parallel elements arranged in parallel between the differential lines, wherein two of the capacitors having same values and forming equivalent capacitance for the passive parallel elements are connected in series; an additional inductor is provided for attenuating a common mode noise connected between a connection point of the two capacitors connected in series and a ground potential, so that attenuation poles for attenuating the common mode noise are formed together with the two capacitors, wherein the lumped-constant differential delay line, the two series capacitors, and the additional inductor are formed as differential delay elements of a section, and a plurality of differential delay elements are arranged in the differential delay line in series in a ladder shape, thus composing a plurality of sections; and each section comprises on each differential line, two equally divided series inductors having a mutual inductance, and the two series capacitors in each section are connected in parallel between respective midpoints of the corresponding two equally divided series inductors.