text: An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found in many electronic devices, such as radio receivers, television sets, radio and television broadcast transmitters, computers, computer peripherals, cellphones, radar, and many other devices.
  Oscillators are often characterized by the frequency of their output signal:
  A low-frequency oscillator (LFO) is an oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
  An audio oscillator produces frequencies in the audio range, 20 Hz to 20 kHz.
  A radio frequency (RF) oscillator produces signals above the audio range, more generally in the range of 100 kHz to 100 GHz.
  There are two general types of electronic oscillators: the linear or harmonic oscillator, and the nonlinear or relaxation oscillator.  The two types are fundamentally different in how oscillation is produced, as well as in the characteristic type of output signal that is generated.