Design Control of Performance in Nested and Interleaved Winding Printed Circuit Board Transformers for Ethernet Applications

Miniature toroidal, ferrite-core, wire-wound transformers are currently used to isolate and interface all Ethernet devices to the twisted pair cable media. Alternative lithographically fabricated transformers with less process variation must be carefully studied to achieve the isolation, insertion loss, and bandwidth requirements of Ethernet networks. In this paper, dielectric-core toroidal transformers fabricated by printed circuit board methods are studied. The transformer inductances and parasitic capacitances were found to trade-off as the dimensions of the wedge-shaped turns were varied; the winding mode and turn number were also changed. Core layer thickness was found to significantly change the magnitude of intra-winding capacitance. Loading behavior is also examined.