oscillator, electronic, electronic circuit that produces an output signal of a specific frequency. An oscillator generally consists of an amplifier having part of its output returned to the input by means of a feedback loop; the necessary and sufficient condition for oscillation is that the signal, in passing from input to output and back to input via the feedback loop, arrive at the input with no change in amplitude or phase. If this condition is met for only a single frequency, the output is a pure sine wave; if it is met for more than one frequency, the output is a complex wave. Some oscillators are designed to operate under certain conditions so that the output is a square wave, a triangular wave, or a pulse. In some cases, a very stable mechanical oscillator, such as a specially prepared quartz crystal, may be coupled to an electronic oscillator to enhance its frequency stability. The frequency of a voltage-controlled oscillator, used in frequency modulation, is automatically adjusted by a small control current.

Mechanical or electronic device that produces a back-and-forth periodic motion. A pendulum is a simple mechanical oscillator that swings with a constant amplitude, requiring the addition of energy at each swing only to compensate for the energy lost because of air resistance or friction. In electronic oscillators, electrons oscillate with a constant period and also require the addition of energy to replace energy loss. Electronic oscillators are used to generate alternating current and high-frequency currents for carrier waves in radio broadcasting. They are incorporated in a wide variety of electronic equipment.

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