3-4
The length of the pulse measured in time (T0 to T1) is referred to as the PULSE WIDTH (pw). The
left side of the pulse is called the LEADING EDGE and the right side is called the TRAILING EDGE.
Time is required for a voltage or current to change in amplitude. The interval of time needed for the
voltage to go from 0 to 100 percent (or from 100 to 0 percent) of its maximum value is called the
TRANSIENT INTERVAL. The two types of transient intervals are RISE TIME and FALL TIME. Rise
time is more accurately defined as the time required for the voltage to build up from 10 percent to 90
percent of the maximum amplitude point. Fall time is the time required for the voltage to drop from 90
percent to 10 percent of the maximum amplitude point.
In this text you will be presented with information in which waveforms appear to have instantaneous
rise and fall times. This is done to simplify the presentation of the material. In reality these waveforms do
have rise and fall times (transient intervals).
Rectangular Wave
A rectangular wave is similar to the square wave. The difference is that in the rectangular waveform,
the two alternations of the waveform are of unequal time duration. Figure 3-1, view (C), shows that the
negative alternation (pulse) is shorter (in time) than the positive alternation. The negative alternation
could be represented as the longer of the two alternations. Either way, the appearance is that of a
rectangle.
Sawtooth Wave
The SAWTOOTH waveform is shown in figure 3-1, view (D). A sawtooth wave resembles the teeth
of a saw blade. There is a rapid vertical rise of voltage from T0 to T1, which is linear (straight). At T1 this
voltage abruptly falls (essentially no time used) to its previous static value. The voltage remains at this
value until T2 when it again has a linear rise. You can see this action in an oscilloscope where there are
two voltage input locations, vertical and horizontal. If you apply a linear voltage to the vertical input, the
electron beam will be forced to move in a vertical direction on the crt. A linear voltage applied to the
horizontal input will cause the electron beam to move horizontally across the crt. The application of two
linear voltages, one to the vertical input and one to the horizontal input at the same time, will cause the
