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Time-Dependent Signal Sources
Figure 11.44 illustrates the convention that will be employed to denote time-dependent signal sources.
One of the most important classes of time-dependent signals is that of periodic signals. These signals
appear frequently in practical applications and are a useful approximation of many physical phenomena.
A periodic signal x(t) is a signal that satisfies the following equation:
(
xt() = xt + nT) n = 1, 2, 3,… (11.41)

where T is the period of x(t). Figure 11.45 illustrates a number of the periodic waveforms that are typically
encountered in the study of electrical circuits. Waveforms such as the sine, triangle, square, pulse, and
sawtooth waves are provided in the form of voltages (or, less frequently, currents) by commercially
available signal (or waveform) generators. Such instruments allow for selection of the waveform peak
amplitude, and of its period.
As stated in the introduction, sinusoidal waveforms constitute by far the most important class of time-
dependent signals. Figure 11.46 depicts the relevant parameters of a sinusoidal waveform. A generalized
sinusoid is defined as follows:

xt() = A cos wt + f) (11.42)
(

FIGURE 11.44 Time-dependent signal sources.

FIGURE 11.45 Periodic signal waveforms.

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