Electronic circuit design ee 233 final presentation

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ELECTRONIC CIRCUIT DESIGN EE 233

• FINAL PROJECT PRESENTATION

• BEEE ( SEMESTER-SPRING 2015)

• ABASYN UNIVERSITY ISLAMABAD

• PRESENTED TO:

THE MOST RESPECTABLE

• SIR WAQAS AHMAD

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Group Members:Waseem Abbas Maneri 0379

Faraz Ahmad 0378

Afzaal Hasnain 03343


Title:Hartley and Colpitts Oscillators.

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HARTLEY AND COLPITTS OSCILLATORS. (FINAL PRESENTATION)

Outline…..

1. Hartley Oscillator

I. Introduction

II. Circuit Diagram

III. Circuit Components and Operation

IV. Tank Circuit

V. Applications

VI. Advantages and Disadvantages

2. Colpitts Oscillator

VII. Intro….

VIII.Circuit and Operation

IX. Advantages and Disadvantages

3. References 5


What is Oscillator..?An oscillator is a mechanical or electronic device that works on the principles of oscillation.

o Oscillation: A periodic fluctuation b/w two things based on energy.

Computer, clocks,watches,radios and metal detectors are among the many devices that uses oscillators.

“OR”

The electronic circuit that produce periodically oscillating electronic signals such as sine wave, square wave or any other wave is termed as Oscillator.

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Hartley Oscillator.Hartley oscillator was invented in 1915 by the American engineer Ralph Hartley while he was working for the Western Electric company. The original design was tube based and he got a patent for it in the year 1920.

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Basic Circuit Diagram:

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Circuit Components & its Operation:In the circuit diagram:

When input is applied

• R1 and R2 give a potential divider bias for the transistor Q1.

• Re is the emitter resistor, whose job is to provide thermal stability for the transistor.

• Ce is the emitter by pass capacitors, which by-passes the amplified AC signals.

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Operation Continue…

• Cin is the input DC decoupling capacitor while Cout is the output DC decoupling capacitor.

• The task of a DC decoupling capacitor is to prevent DC voltages from reaching the succeeding stage.

• Inductor L1, L2 and capacitor C1 forms the circuit named as Tank Circuit.

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Tank Circuit:Components

I. 2 inductors

II. 1 capacitor

Function:

The function of Tank Circuit is to determine the oscillation frequency,

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Operation Continue… Supply ON

Ic Increases

C1 [Charging & discharging]

This create oscillation in Tank circuit.[Key]

Vout inphase with VL1 & 180o out of phase with VL2.

VL2 is fedback to BQ1[Creates another 180

phase shift]

Total Phase Shift=360o

An important condition for creating oscillation.

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Frequency of the Hartley oscillator. Frequency expressed by the given

formula.

C is the Capacitance [Tank Circuit].

LT=L1+L2 [Tank Circuit] [different cores]

L=L1+L2+2M [same core].

Where M is mutual inductance b/w the coils.

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http://www.circuitstoday.com/wp-content/uploads/2009/10/hartley-oscillator-frequency.png


Application:1) Hartley oscillators are

mainly used in radio receivers.

2) Particularly uses for good quality sine wave signal.

3) Useful for the use in RF range frequency .

4) Due to its wide range of frequencies it is the most popular oscillator (30 KHz to 30 MHz).

5) Above this range Colpitts oscillator is preferred.

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Advantages & Disadvantages :

Advantages The frequency is simply varied by the net value of C

in the tank circuit.

The output amplitude remains constant when tuned over the frequency range.

The feedback ratio of L1 to L2 remains constant.

Disadvantages The output is rich in harmonic content and therefore

not suitable where a pure sine wave is required.

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Colpitts Oscillator:The Colpitts Oscillator, (named after its inventor Edwin Colpitts) is another type of LC oscillator design. In many ways, the Colpitts oscillator is the exact opposite of the Hartley Oscillator we have discussed in previous slides. Just like the Hartley oscillator, the tuned tank circuit consists of an LC resonance sub-circuit connected between the collector and the base of a single stage transistor amplifier producing a sinusoidal output waveform.

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Circuit components & its operation: This circuit is very similar in

operation to the Hartley oscillator

But the Colpitts LC tank circuit consists of a single inductor and two capacitors.

The values of the two capacitors (connected in series) are chosen so their total capacitance in series(CTOT), is given by:

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Operation….

Colpitts Tank Circuit: Uses a capacitive voltage divider network as

its feedback source.

C1 and C2 are placed across a single common inductor, L as shown.

Advantage is that (Less mutual inductance= freq.. Stability is improved)

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Operation…. When Supply ON. C1 & C2 start (charg…&

discharg…) When C1,C2 (fully dischar..) the

E.S energy gets transferred into the inductor as magnetic flux.

Inductor start discharg.. & the capacitors gets charged again.

As a result Oscillations are produced due to the back and forth transfer of energy b/w inductors and capacitors.

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Continue… Vc2 has opposite phase to that of Vc1.

Vc2 is fedback to the base of transistor which appears in the amplified form on the output side of transistor [across collector-emitter].

Tank ckt produce 180o P.shift and transistor produce another 180o P.shift.

As the result Input=Output [inphase]

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Frequency of Oscillation:Frequency can be find by the given formula

Where L = inductance, C = effective capacitance, If C1 and C2 are the

individual capacitance, then

C= (C1C2)/(C1+C2).

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Advantages and Disadvantages:

Advantages:

1. Good wave purity .

2. Fine performer at high frequency .

3. Good stability at high frequency .

4. Wide operation range 1 to 60 MHz .

Disadvantages:

5. Poor isolation (Load impedance vs.. frequency) .

6. Hard to design .

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References: www.electronics-tutorials.ws › Oscillator

www.learnabout-electronics.org/Oscillators/osc21.php

www.learnabout-electronics.org/Oscillators/osc21.php

https://www.elprocus.com/colpitts-oscillator

www.circuitstoday.com/colpitts-oscillator

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http://www.learnabout-electronics.org/Oscillators/osc21.php












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Date post:	28-Jul-2015
Category:	Engineering
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Electronic circuit design ee 233 final presentation

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