TABLE OF CONTENTS Tomas Fetter
The simplest useful definition for a signal is an electrical voltage (or current) that varies with time. To characterize a signal, an intuitive yet accurate concept is to define the signal s waveform. A waveform is easy to visualize by imagining the picture a pen, moving up and down in proportion to the signal voltage, would draw on a strip of paper being steadily pulled at right angles to the pen s movement. Shown in Fig. 25.3.1 is a typical periodic waveform and its dimensions. A signal source, or signal generator, is an electronic instrument that generates a signal according to the user s commands with regard to its waveform (Fig. 25.3.2). Signal sources serve the frequent need in engineering and scientific work for energizing a circuit or system with a signal whose characteristics are known.
Most signals fall into one of two broad categories periodic and nonperiodic. Signal source instruments generate one or the other, and sometimes both. A periodic signal has a waveshape, which is repetitive: the pen, after drawing one period of the signal waveform, is in the same vertical position where it began, and then it...
