- Oscillator Definition:: An oscillator is a circuit that converts direct current from a DC source into a continuous alternating waveform, typically without any external input.
- Energy Dynamics: Oscillators maintain their output by converting electrical energy into electromagnetic energy and back, using components like capacitors and inductors.
- Feedback Mechanisms: The sustainability of oscillations in an oscillator circuit is achieved through feedback mechanisms that compensate for energy losses.
- Types of Oscillators: Oscillators vary broadly in types, including harmonic for low-distortion outputs and relaxation for generating various waveform shapes like saw-tooth or square.
- Practical Applications: Oscillators are crucial in technology for generating precise frequencies needed in devices like watches, radios, and computers.
What is an Oscillator?
An oscillator is a circuit that makes a continuous alternating wave from a DC supply, with no separate AC input. Its parts set the frequency of that wave.
The idea is easiest to see in the LC tank of Figure 1, which uses an inductor L and a pre-charged capacitor C. The capacitor first discharges through the inductor, so electric energy becomes a magnetic field in the inductor. When the capacitor is empty, current in the loop is zero.
However, by then, the stored electromagnetic field would have generated a back-emf which results in the flow of current through the circuit in the same direction as that of before. This current flow through the circuit continues until the electromagnetic field collapses which result in the back-conversion of electromagnetic energy into electrical form, causing the cycle to repeat. However, now the capacitor would have charged with the opposite polarity, due to which one gets an oscillating waveform as the output.
Those swings cannot last. Circuit resistance burns energy, so the amplitude falls until the wave dies. That is a damped oscillation.
A continuous wave of fixed amplitude therefore needs the lost energy put back. The energy added each cycle must match the energy lost, or the amplitude will not stay put.
This is because, if the energy supplied is more than the energy lost, then the amplitude of the oscillations will increase (Figure 2a) leading to a distorted output; while if the energy supplied is less than the energy lost, then the amplitude of the oscillations will decrease (Figure 2b) leading to unsustainable oscillations.
In practice the oscillators are amplifiers with positive (regenerative) feedback: part of the output is sent back to the input (Figure 3). The gain comes from an active element such as a transistor or an Op-Amp. The in-phase feedback replaces the energy the tank loses.
Once the power supply is switched ON, the oscillations will be initiated in the system due to the electronic noise present in it. This noise signal travels around the loop, gets amplified and converges to a single frequency sine wave very quickly. The expression for the closed-loop gain of the oscillator shown in Figure 3 is given as:
Where A is the voltage gain of the amplifier and β is the gain of the feedback network. Here, if Aβ > 1, then the oscillations will increase in amplitude (Figure 2a); while if Aβ < 1, then the oscillations will be damped (Figure 2b). On the other hand, Aβ = 1 leads to the oscillations which are of constant amplitude (Figure 2c). In other words, this indicates that if the feedback loop gain is small, then the oscillation dies-out, while if the gain of the feedback loop is large, then the output will be distorted; and only if the gain of feedback is unity, then the oscillations will be of constant amplitude leading to self-sustained oscillatory circuit.
Type of Oscillator
Oscillators fall into two groups: harmonic oscillators (also called linear oscillators) and relaxation oscillators.
In a harmonic oscillator, the energy flow is always from the active components to the passive components and the frequency of oscillations is decided by the feedback path.
Whereas in a relaxation oscillator, the energy is exchanged between the active and the passive components and the frequency of oscillations is determined by the charging and discharging time-constants involved in the process. Further, harmonic oscillators produce low-distorted sine-wave outputs while the relaxation oscillators generate non-sinusoidal (saw-tooth, triangular or square) wave-forms.
The main types of Oscillators include:
- Wien Bridge Oscillator
- RC Phase Shift Oscillator
- Hartley Oscillator
- Voltage Controlled Oscillator
- Colpitts Oscillator
- Clapp Oscillators
- Crystal Oscillators
- Armstrong Oscillator
- Tuned Collector Oscillator
- Gunn Oscillator
- Cross-Coupled Oscillators
- Ring Oscillators
- Dynatron Oscillators
- Meissner Oscillators
- Opto-Electronic Oscillators
- Pierce Oscillators
- Robinson Oscillators
- Tri-tet Oscillators
- Pearson-Anson Oscillators
- Delay-Line Oscillators
- Royer Oscillators
- Electron Coupled Oscillators
- Multi-Wave Oscillators
Oscillators can be also be classified into various types depending on the parameter considered i.e. based on the feedback mechanism, the shape of the output waveform, etc.. These classifications types have been given below:
- Classification Based on the Feedback Mechanism: Positive Feedback Oscillators and Negative Feedback Oscillators.
- Classification Based on the Shape of the Output Waveform: Sine Wave Oscillators, Square or Rectangular Wave oscillators, Sweep Oscillators (which produce saw-tooth output waveform), etc.
- Classification Based on the Frequency of the Output Signal: Low-Frequency Oscillators, Audio Oscillators (whose output frequency is of audio range), Radio Frequency Oscillators, High-Frequency Oscillators, Very High-Frequency Oscillators, Ultra High-Frequency Oscillators, etc.
- Classification Based on the type of the Frequency Control Used: RC Oscillators, LC Oscillators, Crystal Oscillators (which use a quartz crystal to result in a frequency stabilized output waveform), etc.
- Classification Based on the Nature of the Frequency of Output Waveform: Fixed Frequency Oscillators and Variable or Tunable Frequency Oscillators.
Oscillator Applications
Oscillator Applications: Oscillators are a practical way to produce a chosen frequency. An RC oscillator is used at low frequency. An LC oscillator is used at high frequency. An op-amp oscillator is used when the frequency must stay put.
The frequency of oscillation can be varied by varying the component value with potentiometer arrangements.
Some common applications of oscillators include:
- Quartz watches (which uses a crystal oscillator)
- Used in various audio systems and video systems
- Used in various radio, TV, and other communication devices
- Used in computers, metal detectors, stun guns, inverters, ultrasonic and radio frequency applications.
- Used to generate clock pulses for microprocessors and micro-controllers
- Used in alarms and buzzes
- Used in metal detectors, stun guns, inverters, and ultrasonic
- Used to operate decorative lights (e.g. dancing lights)
