A contactless electromagnetic sensor device for determining displacements of a rotor (120) is disclosed. Two sensing coils (612, 614) interact with surfaces of the rotor. A bridge circuit is formed by the sensing coils and by two secondary windings (212, 213) of an input transformer (210). The primary winding of the input transformer receives an excitation signal. An output signal is obtained at an output tap formed by a common node between the sensing coils (612, 614) and a common node between the secondary windings of the input transformer. In this manner excitation and detection are separated. If cables are used for connecting the bridge circuit to signal processing circuitry, the input and output impedances of the bridge circuit can be matched to the characteristic impedance of the cables. An output transformer can be connected to the output tap. The roles of the input and output transformers can be interchanged.