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    Topic 2

    Oscillators

    1

    Sudahkah anda mengisi COURSE

    ENTRANCE SURVEY? Hanya 4

    orang sahaja yang mengisinyasehingga 16/1/2013

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    COURSE LEARNING OUTCOMES

    (CLO)

    CLO1. explain correctly the principles of electronic

    circuits by using block diagram or circuit diagram (C4)CLO2. conduct the construction of electronic circuits

    application during practical works based on the theory

    and principle operation of the circuits. (P4)

    CLO3. deliver an oral presentation to display good

    communication skills. (A2)

    2

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    LEARNING OUTCOMES

    Upon completion of this topic students should be able to:

    Draw block diagram of an oscillator2.1

    Explain requirements of oscillator circuit2.2

    2.3

    2.4

    2.5

    Construct the oscillator circuit

    Explain applications each oscillator

    Compare the performance of the oscillator

    3

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    Oscillator

    Oscillators are devices that can

    convert the DC voltage to AC voltage

    without any external source at a

    particular frequency.

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    Basic oscillator block diagram

    5

    http://localhost/var/www/apps/conversion/tmp/Oscilator.FLV
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    Oscillator

    Oscillator is divided into two classes

    depending on the waveform produced as

    follows:

    i. Harmonic oscillator - the sine wave.ii. Non-harmonic oscillator - in terms of the

    fourth wave, triangle wave, etc..

    6

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    Oscillator

    7

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    Oscillator circuit

    All the basic oscillator circuit consists of

    three parts:

    i. Amplifier

    ii. Feedback

    iii. Frequency Generation Circuit

    8

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    Block diagram of oscillator

    circuit

    9

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    Question

    Draw the block diagram of an oscillator

    and name each block

    10

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    Answer

    11

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    Amplifier

    Generally, an amplifier or simply amp is a

    device for increasing the power of a signal.

    For electronic amplifier, the input "signal"

    is usually a voltage or a current.

    In this case oscillator requires DC power

    supply to produce output. That means this

    DC power supply is used as an input of

    the amplifier

    12

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    Feedback

    Feedback is a condition where part of the

    output signal supplied to the input.

    Since the oscillator has no input signal, thefeedback signal is the input signal to the

    amplifier in the oscillator circuit.

    13

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    Feedback

    There are two principles of feedback,

    positive feedback and negative feedback.

    Oscillators using the principle of positive

    feedback.

    14

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    Concept feedback

    15

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    Feedback

    16

    Figure below shows the basic block diagram of a feedback

    system that are commonly used:

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    Feedback

    17

    A di ill d f i i h

    http://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Audio_oscillator
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    Frequency generation circuit

    Generally, the frequency of the oscillator

    circuit generation in consumer goods is

    divided into two categories:

    i.Audio frequency oscillator whichgenerates: Oscillator Network RC

    (resistance-capacitor). It is to produce low

    and medium frequency signal.Example is the oscillator RC type oscillator

    phase shift and Wein bridge Oscillator.

    18

    An audio oscillatorproduces frequencies in the

    audiorange, about 16 Hz to 20 kHz

    A l f ill t (LFO) i l t i ill t th t t f b l

    http://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillation
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    Frequency generation circuit

    ii. Radio frequency generating oscillator:

    Oscillator Networks LC(inductor-

    capacitor). It is also known as tank circuits.

    It is to produce a high frequency signal (>1MHz), and usually it produces a stable

    frequency.

    LC oscillator is an example ofArmstrongOscillator, Colpitts, Hartley and crystal.

    19

    An RF oscillator produces signals in the radio frequency(RF) range of about 100 kHz to

    100 GHz

    A low-frequency oscillator(LFO) is an electronic oscillator that generates a frequency below

    20Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an

    audio frequency oscillator.

    http://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Synthesizershttp://en.wikipedia.org/wiki/Synthesizershttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Radio_frequency
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    RC Oscillator

    Combination of resistors and capacitors.

    Operate in low frequency. Two types of

    RC oscillator:-

    Phase shift oscillator

    Wein bridge oscillator

    20

    http://localhost/var/www/apps/conversion/tmp/scratch_1//upload.wikimedia.org/wikipedia/commons/c/c5/RC_phase_shift_oscillator.svg
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    LC Oscillator

    Armstrong Oscillator

    Crystal Oscillator Hartley Oscillator

    Colpitts Oscillator

    21

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    LC Oscillator

    Combination of inductor and

    capacitor.

    Operate in high frequency

    22

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    Armstrong Oscillator

    23

    Using a combination of a transformer to step the phase of 180.

    FREQUENCY-DETERMINING DEVICEFEEDBACK NETWORK

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    Operation

    Resistors R1, R2 and R3 is usage

    to provide bias voltage to the

    transistor. Capacitors C1 and C2are used to block an alternating

    signal. This configuration will

    provide 180phase difference ofoutput signal.

    24

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    Operation

    The transformer Tr is selected to produce

    a phase shift of 180 to get the feedback

    voltage in phase with the input transistor.

    Usually the ratio between the coil windings

    L1 with L2 coil arranged.

    So that the product of the gain, A, with the

    feedback factor, , is a (| A| = 1).

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    The frequency of oscillation

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    Colpitts Oscillator

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    Using a separate capacitor for resonant circuit.

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    Operation

    The amplifier will provide 180 phase

    difference of the output signal. LC circuit in

    the feedback loop will produce a phaseshift of 180. So the feedback voltage will

    be in phase with the input voltage on the

    transistor.

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    The frequency of oscillation

    30

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    Example

    A Colpitts Oscillatorcircuit having two capacitors of 10pF and

    100pF respectively are connected in parallel with an inductor of10mH.

    Determine the frequency of oscillations of the circuit.

    The frequency of oscillations for a Colpitts Oscillator is given as:

    The circuit consists of two capacitors in series, so the total capacitance is given as:

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    The inductor is of 10mH then the frequency of oscillation is:

    Then the frequency of oscillations for the Oscillator is 527.8kHz

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    Hartley Oscillator

    34

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    R1

    R2

    RE

    RFC

    C1

    LP

    VCC

    vout

    R1

    R2

    RE

    RFC

    C1

    L1

    VCC

    vout

    L2

    Hartley oscillator.

    1 2

    1

    1