In this lecture, we are going to learn about the Oscillator, the definition of the oscillator, the principle, the block diagram, and the types of oscillators in detail.

## What is an Oscillator?

Oscillators are basically AC signal generators that you use in your laboratories. Oscillators generate a sinusoidal voltage of the desired magnitude, at the desired frequency.

The output voltage and frequency of an oscillator can be variable.

The oscillator operates on a DC power supply +V volts and more importantly, it produces an alternating output voltage without any alternating input voltage.

## Principle of Oscillator

An oscillator is basically an amplifier that does not have any AC input but it operates on the principle of positive feedback to generate an AC signal at its output.

Thus it is clear that an amplifier can work as an oscillator if positive feedback is made to exist.

An amplifier will work as an oscillator if and only if it satisfies a set of conditions called the “Barkhausen Criterion for Oscillation“

## Types of Oscillators

The oscillator can be classified based on various factors such as the shape of the output voltage or the types of components used, the range of operating frequency, and whether the feedback is being used or not.

Let us classify the oscillators based on these factors one by one.

### Types of Oscillators based on the Nature of Output Voltage

The oscillator output voltage can be either sinusoidal or non-sinusoidal. So we can classify the oscillators as sinewave oscillators and non-sinusoidal oscillators.

An example of a sinusoidal oscillator is:

sinusoidal oscillators | |
---|---|

1. | RC-Phase shift oscillator |

2. | Wein bridge oscillator |

3. | Hartley Oscillator |

4. | Colpitts Oscillator |

5. | Clapp oscillator |

The non-sinusoidal oscillators can produce either square wave or triangular, ramp waves at their output. Multivibrators of all kinds are the square wave oscillators.

### Types of Oscillators Based on Components Used

Depending on the components used for the feedback network, the oscillators are classified as RC oscillators and LC oscillators.

The RC oscillators use only resistor (R) and capacitor (C) in their feedback network whereas the LC oscillators use inductors (L) and capacitors (C).

Examples of RC oscillators are RC phase shift oscillators and Wien bridge oscillators whereas Hartley, Colpitt’s and Clapp oscillators are the well-known example of LC oscillators.

### Types of Oscillators based on Range of Operating Frequency

Based on the range of frequency the oscillators can be divided into two categories namely low-frequency (LF) oscillators and high-frequency (HF) or radio-frequency (RF) oscillators.

The frequency range of LF oscillators is approximately from 20 Hz to 100 kHz and they are generally RC oscillators. The operating frequency for the HF oscillators is in the range of 100 kHz to a few GHz. These are LC oscillators.

### Types of Oscillators based on Presenes or Absence of Feedback

The oscillator can be classified as those which use positive feedback and are dependent on the feedback for their operation. The phase shift, Wien bridge, Hartley, Colpitts, Clapp, etc. oscillators are feedback-type oscillators.

The other category of oscillators does not use feedback at all. They are called non-feedback-type oscillators. The UJT relaxation oscillator is the best example of such an oscillator.