oscillators generate complex
waveforms such as
those just discussed. Because the
outputs of these oscillators are
generally characterized by a sudden
change, or relaxation, these oscillators are often called RELAXATION
OSCILLATORS. The pulse repetition rate of these oscillators is usually governed
by the charge and discharge timing of a capacitor in series with a resistor.
However, some oscillators contain inductors
that along with circuit resistance, affect the output frequency. These RC and
LC networks within oscillator circuits are used for frequency determination.
Within this category of relaxation oscillators are MULTIVIBRATORS,BLOCKING
OSCILLATORS, and SAWTOOTH- and TRAPEZOIDAL-WAVE GENERATORS. Many electronic
circuits are not in an "on" condition all of the time. In computers,
for example, waveforms must be turned on and off for specific lengths of time.
The time intervals vary from tenths of
microseconds to several thousand microseconds. Square and rectangular waveforms
are normally used to turn such circuits on and off because the sharp leading
and trailing edges make them ideal for timing purposes.