Oscillators

Oscillators are devices that are used to generate repetitive signals. They produce output signals without an input signal. There are two major types of electronic oscillators: harmonic oscillators and relaxation oscillators. Harmonic oscillators produce sine wave outputs. Relaxation oscillators produce square wave, rectangular wave, and sawtooth outputs. For both types of devices, an active component (normally, in the feedback loop) determines the frequency of oscillation. This active component can be either an electronic circuit or a crystal. Voltage-controlled oscillators (VCO) and voltage-controlled crystal oscillators (VCXO) change the frequency in direct proportion to a control voltage. Basic crystal oscillators (XO) do not. Temperature-compensated crystal oscillators (TCXO) use a thermistor network to generate a correction voltage to reduce frequency deviations over temperature. Oven-controlled crystal oscillators (OCXO) use temperature control circuitry to hold the crystal and its circuitry at a precise, constant temperature. Other oscillator types include voltage-controlled, temperature-compensated crystal oscillators (VCTCXO); oven-controlled, voltage-controlled crystal oscillators (OCVCXO); and digital, temperature-compensated, crystal oscillators (DTCXO). Microcomputer-compensated crystal oscillators (MCXO) and rubidium crystal oscillators (MCXO) are also available.   

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