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Voltage-controlled Oscillator





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 .


VOLTAGE CONTROLLED CRYSTAL OSCILLATORS (VCXO)


A voltage-controlled Crystal Oscillator 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.




APPLICATIONS

VCOs are used in:


SEE ALSO