Low-bias inductors

High-speed data transmissions centering on Internet are spreading not only to corporations, schools, and government offices, but also to households at large. Asymmetric Digital Subscriber Line (ADSL) in particular is spreading rapidly in many countries due to its receptivity to existing telephone networks without requiring a new communications infrastructure. In response, we reviewed the pulse transformers used in ADSL and examined core shape optimization techniques for ADSL pulse transformers. To realize high-fidelity and wide-band transmission of signals, ADSL pulse transformers must have a low total harmonic distortion (THD) characteristic. Essential to a low THD is the linearity of dc bias (or constancy of μ in the B-H loop). We therefore probed bias moderation factors, applying magnetic field analysis to two major core shapes, namely toroidal and EI. The results indicated that the linearity of dc bias is greatly influenced by the magnetic flux density distribution. We found that toroidal is better than EI in a weak magnetic field condition and that a smaller core thickness is better than a greater core thickness under all conditions.