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PRESENTATIONON

OSCILLATORS

Submitted To:- Submitted By:-Mr. Yogesh Kumar Navjyoti SharmaAssistant Professor B.TECH II YEARElectrical Engineering Electrical Engineering

Introduction Classification of Oscillators Tuned Collector Oscillator Hartley Oscillator Colpitts Oscillator RC Phase Shift Oscillator Wein Bridge Oscillator Crystal Oscillator Application of Oscillator

CONTENTS

Oscillation means that an effect that repeatedly and regularly fluctuates about the mean value.

Oscillator is 1) An electronic circuit that generates a periodic waveform on

its output without an external signal source. 2) It converts dc noise/signal power to its ac equivalent.3) Oscillator requires a positive feedback(regenerative feedback).

INTRODUCTION

Sine wave

Square wave

Sawtooth wave

1)

INPUT OUTPUT NO INPUT OUTPUT

BIAS BIAS

2) In amplifiers Negative feedback employed, while in oscillators positive feedback employed.

Difference between an amplifier and an oscillator:

Amplifier Oscillator

Gain of oscillators with feedback : A(f)= Where A is forward path gain β is feedback gain Aβ is loop gain For the sustained oscillations the necessary and sufficient conditions are : 1) The loop gain (Aβ) should be greater then or equal to unity (Aβ>1) 2) The net phase shift around the loop must be 2ᴫ or integer multiple of

2ᴫ. These two condition are known as Barkhausen criterion.

CONDITION FOR OSCILLATION

Oscillators are classified as follows:-1) According to output waveform2) According to components used3) According to frequency range

According to output waveform oscillators are classified into two ways

I. Sinusoidal Oscillators: If the generated waveform is sinusoidal or

close to sinusoidal (with a certain frequency) then the oscillator is

said to be a Sinusoidal Oscillator. Example: Hartley Oscillator,

Colpitts oscillator, Wein Bridge Oscillator etc.

II. Non Sinusoidal Oscillators ( Relaxation Oscillators): If the output

waveform is non-sinusoidal, which refers to square/saw-tooth

waveforms, the oscillator is said to be a Relaxation Oscillator.

Example: Triangular Wave Generator, Square Wave Generator etc.

CLASSIFICATION OF OSCILLATORS

According to Components used

I. LC OscillatorsII. RC Oscillators

According to frequency range

A TUNED COLLECTOR diagram as shown below: In this oscillator 2ᴫ phase shift is achieved by transistor and transformer. It is called tuned oscillator because the LC tuned circuit is connected at

the collector. The oscillation frequency is given by: f=

TUNED COLLECTOR OSCILLATOR

HARTLEY OSCILLATOR

The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tank circuit consisting of capacitors and inductors, that is, an LC oscillator.

In Hartley oscillator 2 phase shift can be achieved by transistor which gives 180° phase shift while remaining 180° phase shift is achieved by tapped inductors.

The frequency of oscillation is given by: f˳=

where L(eq) =L1+L2+2M

If mutual inductance(M) is neglected then L(eq) = L1+L2

The Colpitts oscillator is a type of oscillator that uses an LC circuit in

the feedback loop. The feedback network is made up of a pair of tapped capacitors (C1 and

C2) and an inductor L to produce a feedback necessary for oscillations. In Colpitts oscillator 2 phase shift can be achieved by transistor which

gives 180° phase shift while remaining 180° phase shift is achieved by tapped capacitors.

The frequency of oscillation is given by:

f˳= where C(eq)=

COLPITTS OSCILLATOR

The L-C oscillators are not employed at low frequencies because at low frequencies the inductors become large and bulky, hence R-C oscillators are used.

The feedback network is made up of a R-C section to produce a feedback necessary for oscillations.

In R-C phase shift oscillator 2 phase shift can be achieved by transistor which gives 180° phase shift while remaining 180° phase shift is achieved by a R-C phase shift network consist three R-C section.

The frequency of oscillation is given by: f˳= where R(L)= Load or output resistance

RC PHASE SHIFT OSCILLTOR

Wein Bridge oscillator consists a balanced wein bridge for the feedback network.

It also consists two stage amplifier because feedback network provide 0° phase shift.

In Wein Bridge oscillator 2ᴫ phase shift is achieved by two stage amplifier.

The frequency of oscillation is given by: f˳=

If R1=R2=R and C1=C2=C then

f˳=

WEIN BRIDGE OSCILLATOR

Certain crystals like Quartz, Rochelle salt etc. are used for the construction of crystal oscillator.

Its operation is based on the piezoelectric effect i.e. when an a.c. voltage is applied to such crystal its mechanically vibrated ( compressed or stretched) and vice versa.

CRYSTAL OSCILLATOR

Electrical Equivalent of Crystal Oscillator: From the fig. it is clear that there is two resonance a) Series Resonanceb) Parallel Resonance

c) Series Resonance: Occurs due to series capacitor and series inductor. The series resonance frequency is given as

f˳=

Crystal Oscillator(Contd.)

b) Parallel Resonance: Occurs due to series branch(L1-C1-R1) and parallel capacitor (C0). The parallel resonance frequency is given by:

fp= The parallel resonance frequency is always greater than series resonane

frequency.

CRYSTAL OSCILLATOR(CONTD.)

CRYSTAL OSCILLATOR(Contd.) The Crystal oscillator with transistor with impedance curve is shown as: The crystal oscillator gives maximum feedback voltage at parallel

resonance frequency because at this frequency its impedance is maximum.

Oscillators are commonly used in communication circuits. All the communication circuits for different modulation techniques—AM,

FM, PM—the use of an oscillator is must. Oscillator circuits are used in computer peripherals, counters,

timers, calculators, phase-locked loops, digital multimetres, oscilloscopes, and numerous other applications.

APPLICTIONS OF OSCILLTORS