An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.
How Oscillators Work
A basic oscillator is a capacitor and inductor connected together. As the capacitor discharges, the current creates a magnetic field in the inductor. When the capacitor is fully discharged, the field collapses and induces an opposite current that charges the capacitor again. This cycle continues until all the energy is lost through resistance. The frequency of the oscillations depends on the size of the capacitor and inductor.
Every component has some inherent electrical noise, and this noise provides the initial signal for an oscillator. The output noise is sent back to the input as feedback to be filtered and amplified. This process eventually turns the noise into a steady signal.
These are also called sine-wave or sinusoidal oscillators because their output is a sine-wave. There are many different ways of combining components to form these oscillators, and each type has different properties. For example, the Colpitts oscillator uses a voltage divider for feedback, while the Armstrong oscillator uses two inductor coils.
These are also called non-sinusoidal oscillators because their distinctive sharp waveforms are created by non-linear events, such as a sudden capacitor discharge. The frequency of the output signal can be changed by altering the time it takes the capacitor to build up it's charge.
Relaxation oscillators, such as the crystal oscillator, are used as timers and switches in many devices, like digital watches, televisions and computers. Transmitters use harmonic oscillators to create the carrier wave that carries their signal, and radios use them to demodulate the wave to get that signal.