To provide a small balun transformer circuit.

The small balun transformer is provided with a primary and secondary conductor loops. These loops are respectively provided on a substantially plane spiral structure. However, one of the loops, i.e., the first or second loop is preferably provided in a multilayered (laminated) structure. At least one layer of the first or second layer in the multilayered structure provides one of the loops with an increased impedance. The increased impedance for an impedance matching brings advantage of the absence of parasitic capacitance between the primary and secondary layers, which is normally generated in a multilayered structure. In the other embodiments, both conductor loops are provided in the multiplayer structure. Such a structure is particularly useful for a balun circuit with one-to-one impedance matching conditions and also at somewhat low frequency.