The ideal pulse of Fig. 1 has vertical sides, sharp corners, and a flat
peak characteristic; it starts instantaneously at $t_1$ and ends just as abruptly
The waveform of Fig. 1 will be applied in the analysis to follow
in this chapter and will probably appear in the initial investigation of
areas of application beyond the scope of this text.
Fig. 1: Ideal pulse waveform.
Once the fundamental operation of a device, package, or system is clearly understood using
ideal characteristics, the effect of an actual (or true or practical) pulse
must be considered. If an attempt were made to introduce all the differences between an ideal and actual pulse in a single figure, the result
would probably be complex and confusing. A number of waveforms
will therefore be used to define the critical parameters.
The reactive elements of a network, in their effort to prevent instantaneous changes in voltage (capacitor) and current (inductor), establish
a slope to both edges of the pulse waveform, as shown in Fig. 2. The
rising edge of the waveform of Fig. 2 is defined as the edge that
increases from a lower to a higher level.
Fig. 2: Actual pulse waveform.
The falling edge is defined by the region or edge where the waveform
decreases from a higher to a lower level. Since the rising edge is the
first to be encountered (closest to t = 0 s), it is also called the leading
edge. The falling edge always follows the leading edge and is
therefore often called the trailing edge.
Both regions are defined in Figs. 1 and 2.