d) Definition of a signal:
A signal is the physical representation of information
passing through a system from source to recipient
(figure 2).
Any physical quantity containing information can
be called a signal. Physical quantities such as
temperature, pressure, humidity, etc. are
constantly monitored during a process. Usually,
the information conveyed by a signal is a function
of an independent variable, for example time.
signal
Source
information
Information returned
to the recipient
Electronic system
Figure n° 2
a) Analog signal:
It is a signal that varies continuously over time. For
example the temperature of a place during a month is
an analog quantity, the electrical amplitude of the
analog signal would be the true (analog) image of the
signal to be processed, hence the use of the term
“analog”.
a) Digital signal:
It is a signal that varies discretely (discontinuously) over
time, it is a succession of zero (0) and (1), called bits. It
is said to be binary.
The digital signal is much easier to process with
computers
How does the transition from analog signal to digital
signal take place?
The digital conversion of the analog signal called
digitization follows the following steps:
1. Sampling, consists of measuring the amplitude of the
signal at regular time intervals Te.
2. Quantification, which consists in coding these
samples on a certain number of bits.
Figure 3: Signal sampled at Te [2]
NB: The analog signal is converted into a digital signal
using a converter which translates the signal into a
sequence of binary numbers.
NB: the digital aspect is used for transport, storage and
processing.
e) Signal Processing Specialist:
His work would be the implementation of the
electronic part: receive signals, digitize them, group
them and transport them reliably and quickly to the
computers where the actual treatment.
Signal processing techniques find applications today
in all technological fields:
• Telecommunications;
• Multimedia (sound recording and reproduction
techniques and pictures);
• Medical imaging;
• Satellite remote sensing…
