A device that can accept an analogue, i.e. continuous, signal whose amplitude lies within a given range, and produce an equivalent digital signal, i.e. an n-bit parallel binary word that represents this analogue signal. The analogue signal is ‘examined’ at discrete fixed intervals of time by means of a sampling process in order to produce the digital signal. Analogue signals originating from devices such as analogue sensors or tachogenerators may thus be converted into a form that can then be processed by, say, a microprocessor.

The resolution of an A/D converter gives the smallest change in analogue input that can be discriminated by the device. If the resolution of an n-bit A/D converter is Δ‎V, then its range is either

or

according as it is unsigned or signed. In practice, the value of n is usually 8, 10, 12, 14, or 16. Since the resolution is finite, the conversion process introduces quantization noise (see discrete and continuous systems). A/D converters are available in integrated circuit form. See also D/A converter.