Oscillators

It is an electronic circuit that produces a periodic, oscillating signal often a square wave and a sine wave.

Converts direct current from a power supply to an alternating current signal.

Common signals generated by the oscillators includes clock signals, sound signals produced by video games, electronic beepers and broadcast signals by television and radio transmitters.

Introduction

Conditions For Oscillations

The loop phase shift must be 0 ͦ and 360 ͦ .

The loop gain must be slightly greater than unity.

The voltage gain around the closed feedback loop Acl is the product of the amplifier gain Av and the attenuation B of the feedback circuit.

Acl = AvB

A loop gain greater than 1 will rapidly cause the output to saturate at both peaks of the waveform and producing unacceptable distortion.

If the amplifier gain is greater than 100, it will cause the oscillator limit both peaks of the waveform.

Oscillator Circuit

Oscillator Circuit is divided into three sections:

Tank Circuit

Amplifier Circuit

Feedback Circuit

Tank Circuit produces oscillations which are amplified by the transistor and produces amplified output in the collector side.

Amplifier circuit basically amplifying the small sinusoidal oscillations present in the base-emitter circuit and generates output in the amplified form.

Feedback circuit fed back the energy of the collector circuit to the base circuit through the phenomenon of Mutual induction. 

Types Of Oscillator

Oscillator Types

Linear or Harmonic Oscillator

Non Linear or Relaxation oscillator

Feedback Oscillator

Negative Resistance oscillator

LC Oscillator

RC Oscillator

Crystal Oscillator

LC Oscillator

In LC oscillators, the inductor and capacitor are connected in parallel form a Tank circuit.

Tuned circuit can store electrical energy oscillating at its resonant frequency.

Used in radio frequency circuits because of their ease of implementation and good phase noise characteristics. 

Types of LC OscillatorLC Oscillator

Hartley Oscillator Colpitts Oscillator Clapps OscillatorUsed to generate high-frequency waveforms or signals into which the oscillation frequency is determined by a tank circuit comprising of two inductors and one capacitor.

Used to produce an oscillation at certain frequency and it take feedback from the active device from the voltage divider made of two capacitors in series across the inductor.

Constructed from a transistor and positive feedback network using the combination of an inductance with a capacitor for frequency determination.

RC Oscillator

Type of feedback oscilIator consist of an amplifying device, resistor, vacuum tubes and op amps.

To achieve positive feedback output energy is fed back to its input through a network of resistors and capacitors.

RC filter type combinations are preferred to generate sine waves at low frequencies.

Types of RC Oscillator

LC Oscillator

Wien Bridge Oscillator

Phase shift oscillator

Used to generate sine waves at a large range of frequencies and has a two stage RC coupled amplifier circuit that has low distortion and good stability at its resonant frequency

Linear electronic circuit that produces a sine wave output whose output is fed back to its input through a phase shift network consisting of resistors and capacitors in a ladder network. 

Crystal Oscillator

It is an electronic oscillator used to create an electrical signal of precise frequency by using the vibrating crystal mechanical resonance made of piezoelectric material.

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