Some ac waves rise and/or fall in straight, sloping lines as seen on an oscilloscope screen. The slope of the line indicates how fast the magnitude is changing. Such waves are called sawtooth waves because of their appearance. Sawtooth waves are generated by certain electronic test devices. They can also be generated by electronic sound synthesizers.
Fast Rise, Slow Decay
Above Figure shows a sawtooth wave in which the positive-going slope (called the rise) is extremely steep, as with a square wave, but the negative-going slope (called the decay) is not so steep. The period of the wave is the time between points at identical positions on two successive pulses.
Slow Rise, Fast Decay
Another form of sawtooth wave is just the opposite, with a defined, finite rise and an instantaneous decay. This type of wave is often called a ramp because it looks like an incline going upward (Above Fig.). This wave shape is useful for scanning in television sets and oscilloscopes. It tells the electron beam to move, or trace, at constant speed from left to right across the screen during the rise. Then it retraces, or brings the electron beam back, instantaneously during the decay so the beam can trace across the screen again.
Variable Rise and Decay
Sawtooth waves can have rise and decay slopes in an infinite number of different combinations. One common example is shown in Above Figure. In this case, the rise and the decay are both finite and equal. This is known as a triangular wave.