Page 1070 - The Mechatronics Handbook

FIGURE 38.2 Typical analog and digital signals.
information can also be in analog or digital form. Therefore, we have the following four possibilities in a
communication system [21]:
• Analog information transmitted as an analog signal
• Analog information transmitted as a digital signal
• Digital information transmitted as an analog signal
• Digital information transmitted as a digital signal
There may not be a choice regarding the form (analog or digital) of information being generated by
a device. For instance, a voice signal as one speaks, a video signal as generated by a camera, a speed signal
generated by a moving vehicle, and an altitude signal generated by the equipment in a plane will always
be analog in nature; however, there is a choice regarding the form (analog or digital) of information
being transmitted over a transmission medium. Transmitted information could be analog or digital in
nature and information can be easily converted from one form to another.
Each of these possibilities has its pros and cons. When a signal carrying information is transmitted, it
looses its energy and strength and gathers some interference (noise) as it propagates away from the
transmitter. If the energy of the signal is not boosted at some intermediate point, it may attenuate beyond
recognition before it reaches its intended destination. That will certainly be a wasted effort. In order to
boost energy and strength of a signal, it must be amplified (in case of analog signals) and rebuilt (in case
of digital signals). When an analog signal is amplified, the noise also becomes amplified and that certainly
lowers expectations about receiving the signal at its destination in its original (or close to it) form. On the
other hand, digital signals can be processed and reconstructed at any intermediate point and, therefore,
the noise can essentially be filtered out. Moreover, transmission of information in digital form has many

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