Analog and Digital Signals

Analog and Digital Data

Data can be analog or digital. The term analog data refers to information that is continuous;
digital data refers to information that has discrete states. For example, an analog
clock that has hour, minute, and second hands gives information in a continuous form;
the movements of the hands are continuous. On the other hand, a digital clock that
reports the hours and the minutes will change suddenly from 8:05 to 8:06.
Analog data, such as the sounds made by a human voice, take on continuous values.
When someone speaks, an analog wave is created in the air. This can be captured by a
microphone and converted to an analog signal or sampled and converted to a digital
signal.
Digital data take on discrete values. For example, data are stored in computer
memory in the form of Os and 1s. They can be converted to a digital signal or modulated
into an analog signal for transmission across a medium.
Data can be analog or digital. Analog data are continuous and take continuous values.
Digital data have discrete states and take discrete values.

Analog and Digital Signals

Like the data they represent, signals can be either analog or digital. An analog signal
has infinitely many levels of intensity over a period of time. As the wave moves from
value A to value B, it passes through and includes an infinite number of values along its
path. A digital signal, on the other hand, can have only a limited number of defined
values. Although each value can be any number, it is often as simple as 1 and O.
The simplest way to show signals is by plotting them on a pair of perpendicular
axes. The vertical axis represents the value or strength of a signal. The horizontal axis
represents time. Figure 3.1 illustrates an analog signal and a digital signal. The curve
representing the analog signal passes through an infinite number of points. The vertical
lines of the digital signal, however, demonstrate the sudden jump that the signal makes
from value to value.
Signals can be analog or digital. Analog signals can have an infinite number of
values in a range; digital signals can have only a limited number of values.

Periodic and Nonperiodic Signals

Both analog and digital signals can take one of two forms: periodic or nonperiodic
(sometimes refer to as aperiodic, because the prefix a in Greek means "non").
A periodic signal completes a pattern within a measurable time frame, called a
period, and repeats that pattern over subsequent identical periods. The completion of
one full pattern is called a cycle. A nonperiodic signal changes without exhibiting a pattern
or cycle that repeats over time.
Both analog and digital signals can be periodic or nonperiodic. In data communications,
In data communications, we commonly use periodic
analog signals and nonperiodic digital signals.