A mode-switching transformer, combined with a differential low-pass filter, including a first planar winding in a first conductive level having an external end terminal defining a common-mode input/output terminal; a second planar winding electrically in series with the first winding and formed in a second conductive winding; at least one capacitor connecting an external end terminal of the second winding to ground; a third winding formed in the second conductive level and having an external end terminal defining a first differential mode access; and a fourth winding, electrically in series with the third winding and formed in the first conductive level, an external end terminal of the fourth winding defining a second differential-mode access terminal and the central ends of all windings being interconnected to ground.