2. Classification and analysis of different types of coupling

2.1 Common impedance coupling

Common-impedance (or common-element or galvanic) coupling occurs when the electrical currents of two separate systems follow the same path, whose impedance cannot be neglected. Figure 5 , which shows two circuits sharing the same portion of ground conductor, illustrates such coupling. Through the impedance of this common conductor, the return current of one circuit causes a variation in the reference potential of the other; this voltage variation may appear in full in the expression of the output signal v _s , or it may result in the appearance of a common-mode signal.