Subject: Liner Integrated Circuits

Topic: Special Purpose Integrated Circuits

Difficulty: Low

Voltage Controlled Oscillator (VCO)

What is it?

A voltage controlled oscillator is a widely used electronic oscillator where the input tuning voltage determines the oscillation frequency. The output frequency of the voltage controlled oscillator is either sinusoidal or saw-tooth.

Voltage controlled oscillators are important components in many applications such as electronic jamming equipment, function generators and phase-locked loops.

Depending on the waveform, voltage controlled oscillators are categorized into harmonic oscillators and relaxation oscillators. Harmonic or linear oscillators are comprised of a resonator and amplifier and produce a sinusoidal waveform.

An LC-tank oscillator is a harmonic oscillator. In this VCO, voltage across the diode varies the varactor diode’s capacitance. Hence the varactor changes capacitance of the LC circuit thereby the frequency changes.

Relaxation oscillators produce a saw-tooth waveform and require only minimal external components to produce a wide range of operational frequencies. Harmonic oscillators show better frequency stability with respect to external factors like noise, temperature and power. There is better accuracy with respect to frequency control as well in harmonic oscillators. However, they are less suited for monolithic integrated circuit technology, but much better suited for relaxation oscillators. Moreover, relaxation oscillators can provide a wide range of operational frequencies.