Ferrite cores for xDSL: optimum selection

An overview for ferrite core selection (core shapes and materials) for signal applications is given. It is shown that distortion k₃ and insertion loss over the frequency range a_c(f) are the key functions in transformer design for xDSL-applications. Parameters called the core distortion factor (CDF) and shape distortion factor (SDF) are helpful in the selection of the core type. The harmonic distortion under circuit conditions can be calculated with a distortion transformer coefficient (DTC) from k₃. This factor is important in order to correlate the in-circuit third harmonic distortion with the η_B-measurements. DTC considers circuit conditions for known impedance conditions