Introduction of Oscillators

INTRODUCTION OF OSCILLATORS

Any circuit which is used to generate a periodic voltage without an ac input signal is called an oscillator. To generate the periodic voltage the circuit is supplied energy from a dc source. If the output voltage is a sinewave function of time, the oscillator is called a "Sinusoidal" or "Harmonic" oscillator. It is basically an amplifier circuit with positive feedback. Thus the amplifier can be defined as a circuit which self generating some waveform such as sine, triangular, square etc. It is also known as a converter, it converts power from dc power supply into ac power.

Classification of Oscillators

Oscillators are classified into following ways.

1. According to the waveforms generated

(a) Sinusoidal Oscillator

(b) Relaxation Oscillator

2. According to the fundamental mechanisms involved

(a) Negative Resistance Oscillators

(b) Feedback Oscillators

Negative Resistance Oscillator uses negative resistance of the amplifying device to neutralize the positive resistance of the oscillator.

Feedback Oscillator uses positive feedback in the feedback amplifier to satisfy the Barkhausen criterion.

3. According to the frequency generated:

(a) Audio Frequency Oscillator (AFO): upto 20 KHz

(b) Radio Frequency Oscillator (RFO): 20KHz to 30 MHz

(c) Very High Frequency (VHF) Oscillator: 30 MHz to 300 MHz

(d) Ultra High Frequency (UHF) Oscillator: 300 MHz to 3 GHz

(e) Microwave Frequency Oscillator: above 3 GHz

4. According to the type of circuit is used.

Sinewave oscillators may be classified as

(a) LC tuned oscillator

(b) RC phase shift oscillator