What are the Functions of Oscillators in a Circuit?

Posted by Rachel Ye on September 5th, 2019

An oscillator is an electronic component used to generate a repeating electrical signal (usually a sine or square wave). The circuit that constitutes it is called an oscillating circuit. One of the most common oscillators is the pendulum of the clock. If you push the pendulum, it will swing at a certain frequency - back and forth for a certain number of times in each second. The main factor to control the frequency is the length of the pendulum.

The oscillator is a frequency source and is generally used in phase-locked loops. It is a device that can convert DC energy into AC energy without external signal excitation. It can generate electromagnetic waves in radio broadcast and communication equipment, create a clock signal  in the microcomputer, and form high-frequency alternating current in the voltage stabilizing circuits.

To oscillate an object, energy must be converted back and forth between the two forms. For example, in a pendulum, energy is converted between potential energy and kinetic energy. When the pendulum is at one end of the swing, its energy is all potential energy and is ready to fall. When the pendulum is in the middle of the loop, all the potential energy is converted into kinetic energy, and the pendulum moves at its fastest speed. When the pendulum moves to the other side, all kinetic energy turns into potential energy. The conversion of energy between these two forms is the cause of oscillation.

Finally, any physical oscillations will stop due to frictions. To continue exercising, you must add a little energy to each cycle. In the pendulum clock, the energy that keeps the pendulum moving comes from the spring. The pendulum gets a little thrust every time it rings to make up for the energy lost by friction.

There are two main types of oscillators: harmonic oscillators and relaxation oscillators. 

According to the oscillation excitation mode, it can be divided into self-excited oscillators and separate-excited oscillators; 

According to the circuit structure, it can be divided into a capacitance resistance(CR) oscillators, inductance capacitance oscillators, crystal oscillators, tuning fork oscillators, etc. 

According to the output waveform, it can be divided into oscillators of sine wave, square wave and sawtooth wave.

Self-excited multivibrators are also called astable circuits. Each of the collectors of the two tubes has a capacitor connected to the base of the other tube to perform an AC coupling function to form a positive feedback circuit. When the power is turned on, one of the tubes is turned on first and the other tube is turned off. At this time, the collector of the conducting tube has an output, and the capacitance of the collector couples the pulse signal to the base of the other tube to conduct the other tube. At this moment, the originally conducted pipe is cut off. When the two tubes are turned on and off in turn, an oscillating current is generated.

Since the parameters of the device are not exactly the same, the state of the two transistors changes when the power is on. This change become stronger and stronger because of the positive feedback, which leads to a transient steady state. During this state, the other transistor is turned on or off after being gradually charged by the capacitor, and the state is reversed to reach another temporary steady state. This cycle repeated again and again and form oscillation.

There are three basic components of a oscillator:

1. Triode amplifier(for energy control);

2. Positive feedback network (give feedback of part of the output signal to the input);

3. Frequency selective network (to select the required oscillation frequency, so that the oscillator can oscillate at a single frequency, thereby obtaining the required waveform).