Multilayer balun transformer structure
The present invention relates to a multilayer, balanced-unbalanced signal transformer (20) comprising a first coil and a second coil providing at least one balanced signal port at one side of the balun transformer and an unbalanced signal port at another side of the balun transformer. The (at least one) balanced signal port is provided by a first balanced signal terminal (23 b) and a second balanced signal terminal (24 b) formed by the ends of the first coil. The unbalanced (single-ended) signal port is provided by a first unbalanced signal terminal (21 u) and a second unbalanced signal terminal (22 u). It comprises a discrete component formed on a low resistivity, e.g. semiconductor substrate layer, and the first and second coils are formed in, or constitute, a first and a second metal layer such that at least a portion of one of the coils is disposed in a metal layer, or constitute a portion of a metal layer, above the metal layer in which at least a portion of the other coil is disposed, or which is constituted, at least partly, by a portion of the other coil, wherein between said first and second metal layer and between said second metal layer and the substrate layer, first and second dielectric layers are disposed. Each of said first and second coils comprises three or less winding turns.