Ideal versus Actual Pulse Waveform

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 at $t_2$. 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.
Ideal pulse waveform.
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.
Actual pulse waveform.
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.