0195136047.pdf

DIGITAL BUILDING BLOCKS AND COMPUTER SYSTEMS 269

3

v 1 v 2

t

t

2

0 T 1 T 2 T 3 T 4

T 1

T 4

T 2

T 3

1

(a)

(b)

− 1

− 2

− 3

0

Figure 6.0.1Continuous signals.

3

v 3 v 4

t t

2

T 2 0 T 1 T 2 T 3 T 4

T 1 T 3 T 4

1

(a)

− 1 (b)

− 2

− 3

0

Figure 6.0.2Discrete signals.

values to the nearest of a set of discrete amplitudes called quantum levels, a digitized signal can
be obtained as discussed in more detail in Section 15.3.
The most common digital signals arebinary signals. A binary signal is a signal that can take
only one of two discrete values and is therefore characterized by transitions between two states.
Figure 6.0.3 displays typical binary signals.
Voltmeters, for example, can be of either analog or digital (digital voltmeter, or DVM)
variety. While the speedometer of a car is an analog device, the odometer (which records miles
or kilometers) is digital because it records changes in units of one-tenth of a mile or kilometer. A
toggle switch which is either on or off is digital, whereas the dimmer switch is analog because it
allows the light intensity to be varied in a continuous way.
Digital electronic circuits have become increasingly important for several reasons. The
present-day integrated-circuit (IC) technology allows the construction of an enormous number of