A transformer, including a first coil and a second coil. The first coil is magnetically coupled to the second coil. At least one of the first coil and the second coil includes a plurality of sub-coils, and the plurality of sub-coils include a first sub-coil and a second sub-coil. A first magnetic field formed by the first sub-coil passes through a layout plane of the transformer in a first manner, and a second magnetic field formed by the second sub-coil passes through the layout plane in a second manner. The first manner includes passing in from a first surface of the layout plane and passing out from a second surface of the layout plane, and the second manner includes passing in from the second surface and passing out from the first surface.