3. Digital signals

A signal is digital if it carries information in the form of a simple sequence of digits. It is therefore discontinuous both in time (the digits follow one another) and in one of its characteristics (amplitude, frequency or phase, which can only take on a finite number of states).

A natural physical phenomenon is doubly continuous: firstly, it is defined for any value of time, and secondly, for each of these instants, the value is a continuous function in the mathematical sense. It is the measurement operation that makes the instantaneous value of the physical quantity correspond to a number whose precision depends on the measurement device used.

To switch from a continuous analog signal v (t ) to the associated digital signal, two operations are required:

• If T is the constant distance between...