Digital electronics represent signals by discrete bands of analoglevels,
rather than by a continuous range. All levels within a band represent
the same signal state. Relatively small changes to the analog signal
levels due to manufacturing tolerance, signal attenuation or parasitic noise do not leave the discrete envelope, and as a result are ignored by signal state sensing circuitry.
In most cases the number of these states is two, and they are
represented by two voltage bands: one near a reference value (typically
termed as "ground" or zero volts) and a value near the supply voltage,
corresponding to the "false" ("0") and "true" ("1") values of the Boolean domain respectively.
Digital techniques are useful because it is easier to get an
electronic device to switch into one of a number of known states than to
accurately reproduce a continuous range of values.
Digital electronic circuits are usually made from large assemblies of logic gates, simple electronic representations of Boolean logic functions.