Voltage-controlled oscillator

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It has been suggested that VCTCXO be merged into this article or section. (Discuss)

A voltage-controlled oscillator or VCO is an electronic oscillator specifically designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation, or rate of repetition, is varied with an applied DC voltage, while modulating signals may be fed into the VCO to generate frequency modulation (FM), phase modulation (PM), and pulse-width modulation (PWM).

1 Control of frequency in VCOs
2 Voltage-controlled crystal oscillators
3 Applications
4 See also

[edit] Control of frequency in VCOs

For high-frequency VCOs the voltage-controlled element is commonly a varicap diode connected as part of an LC tank circuit. For low-frequency VCOs, other methods of varying the frequency (such as altering the charging rate of a capacitor by means of a voltage controlled current source) are used. See Function generator.

[edit] Voltage-controlled crystal oscillators

A voltage-controlled crystal oscillator (VCXO) is used when the frequency of operation needs to be adjusted by a relatively small amount, or when exact frequency or phase of the oscillator is critical, or, by applying a varying voltage to the control input of the oscillator, to disperse radio-frequency interference over a range of frequencies to make it less objectionable. Typically the frequency of a voltage-controlled crystal oscillator can only be varied by a few tens of parts per million (ppm), because the high Q factor of the crystals allows only a small "pulling" range of frequencies to be produced.

A temperature-compensated VCXO (TCVCXO) is normally used so that temperature does not alter the piezoelectric effect, thereby causing frequency drift due to heat buildup inside of a transmitter.