Patent ID: 7952458

Claim:
A mode-switching transformer with a 1-to-4 impedance ratio comprising: a first planar winding formed in a first conductive level from a first differential mode terminal outside of the winding; a second planar winding formed in a second conductive level from a second differential mode terminal outside of the winding; a via of interconnection of central ends of the first and second windings; and at least one third planar winding in one of the two conductive levels, interdigitated with the first or the second winding from a first common-mode terminal outside of the winding, a central end of the third winding being connected to said via wherein outside ends of the first, second and third planar windings are connected to the first differential mode terminal, the second differential mode terminal and the first common-mode terminal, respectively, at least one fourth planar winding, in the conductive level which does not contain the third planar winding, being interdigitated with the second or first planar winding from an external end, a central end of the fourth planar winding being connected to said via, wherein the external end of the fourth planar winding is unconnected and wherein the central ends of the first, second, third and fourth planar windings are connected to said via for direct grounding.