A current determiner comprising a first input conductor and a first current sensor, formed of a p.lurality of magnetoresistive, anisotropic, ferromagnetic thin-film layers at least two of which are separated from one another by a nonmagnetic layer positioned therebetween, and both supported on a substrate adjacent to but electrically isolated from one another with the first current sensor positioned in those magnetic fields arising from any input currents. A first shield/concentrator of a material exhibiting a substantial magnetic permeability is positioned between the substrate and the first input conductor. The substrate can include a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to the first input conductor. Magnetically permeable material can be provided in supporting structures.