Voltage-controlled oscillator
VCOs are used in synthesizers to generate a waveform whose pitch can be adjusted by a voltage determined by a musical keyboard or other input.
[4] A voltage-controlled capacitor is one method of making an LC oscillator vary its frequency in response to a control voltage.
The same effect occurs with bipolar transistors, as described by Donald[5] E. Thomas at Bell Labs in 1954: with a tank circuit connected to the collector and the modulating audio signal applied between the emitter and the base, a single-transistor FM transmitter is created.
[7] 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).
A voltage-to-frequency converter (VFC) is a special type of VCO designed to be very linear over a wide range of input voltages.
Modeling for VCOs is often not concerned with the amplitude or shape (sinewave, triangle wave, sawtooth) but rather its instantaneous phase.
The effect of flicker noise can be reduced with negative feedback that linearizes the transfer function (for example, emitter degeneration).
A temperature-compensated VCXO (TCVCXO) incorporates components that partially correct the dependence on temperature of the resonant frequency of the crystal.
A smaller range of voltage control then suffices to stabilize the oscillator frequency in applications where temperature varies, such as heat buildup inside a transmitter.
[citation needed] A clock generator is an oscillator that provides a timing signal to synchronize operations in digital circuits.
Jitter is a form of phase noise that must be minimised in applications such as radio receivers, transmitters and measuring equipment.
Function generators are low-frequency oscillators which feature multiple waveforms, typically sine, square, and triangle waves.
Voltage-to-frequency converters are voltage-controlled oscillators with a highly linear relation between applied voltage and frequency.
