Created by Jimmie Fouts

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Oscillators

• Created by Jimmie Fouts
• Houston County Career Academy
• for

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Objectives

• 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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Word Wall

• Oscillation an effect that repeatedly and
  regularly fluctuates about a mean value
• Oscillator circuit that produces oscillation
• Characteristics frequency, amplitude,
  distortion, wave-shape, stability

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Overview of the Oscillator

• 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 high
  frequencies
• Most oscillators are amplifiers with feedback

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Amplifiers as Oscillators?

• Most amplifiers will oscillate when conditions
  are correct
• 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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Electrical Feedback

• Practical oscillators use electrical feedback to
  produce oscillation
• Feedback circuits use resistors, capacitors,
  coils, or transformers to connect a portion of
  the output signal back to the input of the
  amplifier

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Feedback and Amplifier GainConditions for
Oscillation

• 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

• In-phase feedback is also called regenerative
  feedback or positive feedback
• When the original amplifier input and output
  signals are not in-phase, the feedback circuit is
  used to reverse the phase

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Input Characteristics

• Steady source of direct current (DC)
• In many applications, the DC source requires a
  filter

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Output Characteristics

• Amplitude
• Frequency
• Waveform type
• Stability
• On some oscillators, the capability to change
  frequency

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Oscillator Amplitude

• Usually determined by the gain available from the
  amplifier
• Supply voltage and circuit losses affect amplitude

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Oscillator Frequency

• Frequency of operation is normally determined by
  the feedback circuit
• Common feedback circuits used to determine
  oscillator frequency include
• crystals
• resistor and capacitor networks (RC)
• coil and capacitor networks (LC) tank circuit

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Waveform Type

• Generally, determined by
• Feedback circuitry
• Output filter circuitry
• Amplifier gain, or
• Changes to input voltage
• May be sinusoidal (sine wave), square wave, or
  triangular wave

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Oscillator Stability

• 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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Ability to Change Frequency

• Oscillators sometimes have the ability to change
  frequencies
• Crystal oscillator frequency is controlled by
  changing the crystal
• Crystals are usually cut from quartz to generate
  a specified frequency when operating

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VFO

• Variable frequency oscillators (VFO) generally
  use a variable resistor, coil, or capacitor in
  the feedback circuit
• Varying the value of resistance, impedance, or
  reactance in the circuit results in a change of
  the oscillator output

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VCO

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

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Typical Uses of the Oscillator

• Radio and television stations require
  oscillators to develop the basic signal to
  transmit their information

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Typical Uses of the Oscillator

• Cell phones, electronic keyboards, and remote
  controls use oscillators to produce the required
  frequencies for operation

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Typical Uses of the Oscillator

• Digital devices such as computers, watches,
  calculators, and iPods all require oscillators to
  generate the rectangular waveform required for
  operation

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Typical Uses of the Oscillator

• Variable oscillators, known as signal generators,
  are used to generate frequencies and waveforms
  needed for troubleshooting and the testing of
  electronic equipment