ENGR AE 5 OscillatorsPowerPoint

8/12/2019 ENGR AE 5 OscillatorsPowerPoint

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Created by Jimmie FoutsHouston County Career Academy

for


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Define the basic oscillator circuit

Identify elements of feedback in the oscillator

Identify the conditions for oscillation to occur

Identify input and output characteristics Identify the difference between VFO and VCO

oscillators

Identify common uses of the oscillator


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Oscillation: an effect that repeatedly and regularlyfluctuates about a mean value

Oscillator: circuit that produces oscillation

Characteristics: frequency, amplitude, distortion,wave-shape, stability


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One of the basic building blocks of electronics

Input is a direct current (DC) power source

Output is alternating current (AC)

Can generate sub-audible frequencies or very highfrequencies

Most oscillators are amplifiers with feedback


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Most amplifiers will oscillate when conditions arecorrect Example: Too high of a volume on public address system

= loud noise and squeals that are the result of acoustic

waves traveling from the speakers to the microphone

The result is oscillation


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Practical oscillators use electrical feedback to produceoscillation

Feedback circuits use resistors, capacitors, coils, or

transformers to connect a portion of the output signalback to the input of the amplifier


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Feedback alone does not promise oscillation

There is always some loss in the feedback circuit Amplifier gain must be greater than this loss

Feedback must be in-phase


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In-phase feedback is also called regenerative feedbackor positive feedback

When the original amplifier input and output signals

are not in-phase, the feedback circuit is used to reversethe phase


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Steady source of direct current (DC)

In many applications, the DC source requires a filter


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Amplitude

Frequency

Waveform type

Stability On some oscillators, the capability to change frequency


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Usually determined by the gain available from theamplifier

Supply voltage and circuit losses affect amplitude


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Generally, determined by: Feedback circuitry

Output filter circuitry

Amplifier gain, or

Changes to input voltage

May be sinusoidal (sine wave), square wave, ortriangular wave


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Sometimes referred to as a stable oscillator

Source of a signal with consistent amplitude

Source of a signal with consistent frequency


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Oscillators sometimes have the ability to changefrequencies

Crystal oscillator frequency is controlled by changingthe crystal Crystals are usually cut from quartz to generate a

specified frequency when operating


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Variable frequency oscillators (VFO) generally use avariable resistor, coil, or capacitor in the feedbackcircuit

Varying the value of resistance, impedance, orreactance in the circuit results in a change of theoscillator output


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Voltage controlled oscillators (VCO) utilize changes involtage to generate changes in the oscillator output


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Typical Uses of theOscillator

Radio and television

stations require

oscillators to develop

the basic signal to

transmit their

information


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Digital devices such

as computers,

watches, calculators,

and iPods all require

oscillators to

generate the

rectangular

waveform required

for operation


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Variable oscillators,

known as signal

generators, are used

to generate

frequencies and

waveforms needed

for troubleshooting

and the testing of

electronic equipment

Documents

ENGR AE 5 OscillatorsPowerPoint