Integrated transformer balun with enhanced common-mode rejection for radio frequency, microwave, and millimeter-wave integrated circuits

Apparatus and method example embodiments provide an improved common mode rejection ratio in high frequency transformer baluns. According to an example embodiment of the invention, an apparatus comprises a first winding of at least one turn forming a primary coil, having first and second differential leads oriented in a first direction, the primary coil formed in a first conductive layer over a substrate and the first differential lead of the primary coil being grounded; and a second winding of at least one turn forming a secondary coil, having a third and fourth differential leads oriented in a second direction offset by an angle of greater than zero degrees and less than 180 degrees from the first direction, the secondary coil formed in a second conductive layer separated by an insulating layer from the first conductive layer.