3.2 Digital signals

A signal is a time-varying quantity that represents encoded information. We are concerned with electrical signals, which have time-varying voltage and current. An analog signal represents continuous-valued quantities (e.g., real numbers), while a digital signal represents discontinuous-valued quantities (e.g., integers) called discrete quantities, which are typically finite in number. Note, however, that digital signals still have values at each moment of time, it is just that they represent a discrete value.

Many digital signals represent just two discrete values, and often (but not always), this is implied in the use of the term. We will implicitly use "digital" to signify two-valued signals unless otherwise stated. The two-valued binary numeral system is a common way to model digital signals. This is closely tied to the bits stored in computer memory and operated on by a processor; in fact, …