A method for operating electronic apparatus with independent power sources and having a functional circuit and a force and touch sensing circuit, the functional circuit and the force and touch sensing circuit are respectively powered by a first power source and a second power source different with the first power source. The method comprises (a) connecting the first power source and the second power source to different grounds; (b) the force and touch sensing circuit applying a capacitive sensing excitation signal to a force sensing electrode or a touch sensing electrode; and (c) the force and touch sensing circuit detecting a sensing signal from the force sensing electrode or the touch sensing electrode. In above step (b) or (c), the first power source and the second power source have no common current loop therebetween.