Signature analysis consists of mapping the response of a circuit under test into a compact pattern called signature. There is some loss of information and a faulty response may correspond to a fault-free signature; this phenomenon is called aliasing.

General features of signature analysis are presented in Section 12.1. For a single output circuit, a single input signature analyser is used; the properties of this kind of signature analysers are studied in Section 12.2. Section 12.3 is devoted to multiple input signature analysers, which are used for multiple output circuits.