Voltage-controlled oscillator

A voltage-controlled oscillator (VCO) generates a periodic signal whose frequency changes with an applied control voltage. It is a core building block in frequency synthesis and phase-locked loops.

Frequency tuning: The adjustment of an oscillator’s frequency by changing a circuit parameter. A VCO converts changes in its control voltage into frequency tuning.
Phase-locked loop: A feedback system that locks an oscillator’s phase and frequency to a reference signal. Its feedback voltage tunes the VCO until the output tracks the reference.
Oscillation: Repeated variation of a quantity around an equilibrium or through a recurring cycle. A VCO is an electronic source of sustained electrical oscillation.
Numerically controlled oscillator: A digital signal generator whose frequency is set by a numerical tuning word. An NCO tunes frequency digitally, unlike a VCO’s analog control voltage.
Voltage-to-frequency converter: A circuit that produces an output pulse rate or frequency proportional to an input voltage. It also maps voltage to frequency, but typically serves as a signal-conversion circuit rather than a tunable oscillator.
Frequency synthesizer: An electronic system that generates selected frequencies from one or more reference signals. VCOs provide the tunable signal from which synthesized frequencies are produced.
Frequency: The number of cycles of a repeating event per unit time. A VCO’s defining output quantity is its frequency.
Direct digital synthesis: A method that generates waveforms by digitally accumulating phase and converting it to an output signal. DDS offers precise digital tuning as an alternative to analog VCO tuning.
Relaxation oscillator: An oscillator that repeatedly charges and discharges a circuit element to create a periodic waveform. Many VCOs vary a capacitor’s charging rate to tune this oscillator type.
Frequency modulation: A modulation method that encodes information by varying a carrier signal’s frequency. Applying an information signal to a VCO’s control input directly produces frequency modulation.

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