Relaxation oscillators are a type of VCO that use a simple switching mechanism between two stable states to generate an oscillating signal. Unlike harmonic oscillators that produce sinusoidal waveforms, relaxation oscillators generate square or rectangular waveforms. Relaxation oscillators are often used in electronic circuits for timing and pulse generation. They are also commonly found in applications such as timers, oscillators, and switches.
The basic components of a relaxation oscillator are an amplifying stage, a comparator, and a capacitor. The amplifying stage is used to amplify the input signal and drive the comparator, which compares the input signal with a reference voltage. If the input signal exceeds the reference voltage, the comparator switches its output state, charging or discharging the capacitor.
As the capacitor charges or discharges, its voltage changes, causing the input signal to the comparator to change, which in turn switches the comparator's output state. This process repeats continuously, generating an oscillating signal at the output of the comparator. The frequency of the oscillating signal depends on the time constant of the switching elements. The amplitude of the oscillation is proportional to the size of the input voltage.
Relaxation oscillators are relatively simple to design and implement, making them a popular choice for many applications. However, they have some disadvantages compared to harmonic oscillators, including lower frequency stability and lower spectral purity. Additionally, the waveform generated by a relaxation oscillator is not a pure sine wave, which may limit its use in some applications.
One of the most commonly used relaxation oscillators is the Astable Multivibrator, which is a regenerative switching circuit. This is because they are simple, reliable and easy to construct with a constant square wave output.