Digital signal

Basic digital signals rep info in discrete bands of levels. All levels within a band of values represent the same information state. Most digital circuits' signal have 2 possible valid values; a binary or logic signal. They are rep by 2 voltage bands: 1 near a reference value (often termed as ground or 0 V), and the other a value near the supply voltage. These correspond to the 2 values 0 and 1 (or false and true) of the Boolean domain, so at any time a binary signal rep 1 binary digit (bit). Due to such discretization, small changes to the signal levels don't leave the discrete envelope, thus are ignored by signal state sensing circuitry. Thus, digital signals have noise immunity; electronic noise, won't affect digital circuits, whereas noise always degrades the operation of analog signals to some degree.

Digital signals having more than two states are occasionally used; circuitry using such signals is called multivalued logic. For example, signals that can assume three possible states are called three-valued logic.

A digital signal's physical quantity rep the info may be a variable electric current or voltage, the intensity, phase or polarization of an optical or other electromagnetic field, acoustic pressure, the magnetization of a magnetic storage media, etcetera. Digital signals are used in all digital electronics, notably computing equipment and data transmission.