CHAPTER TWENTYNINE

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CHAPTER TWENTY-NINE

• Oscillators and Multivibrators

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OSCILLATORS

• Generate and sustain an AC output
• Require no input signal
• Sine wave and non-sine wave types
• Used in wide variety of circuits and systems

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OSCILLATOR REQUIREMENTS

• Power source
• Frequency-determining components
• Active device to provide gain
• Positive feedback

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LC OSCILLATOR

• LC tank (parallel) circuit determines frequency

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Oscillator Types

• Hartley Crystal
• Colpitts Clapp
• RC Wien-Bridge

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Hartley Oscillator
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COLPITTS

• Similar to Hartley oscillator
• Tapped ground in capacitor circuit

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EXAMPLE CIRCUIT
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CLAPP OSCILLATOR

• Modified Colpitts oscillator
• Modification done to improve stability

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EXAMPLE CIRCUIT
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CRYSTAL OSCILLATOR

• Uses crystal for frequency-determining component
  (parallel)
• Uses crystal in feedback path to frequency
  determining components (series)
• Very stable circuit

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EXAMPLE CIRCUIT
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RC OSCILLATOR

• Generates a sine wave
• Uses phase shift of RC network for required
  circuit phase shift
• Uses three RC segments
• Low stability

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EXAMPLE CIRCUIT
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WIEN-BRIDGE

• Simple
• Stable
• Popular
• Uses resistor and capacitor

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EXAMPLE CIRCUIT
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MULTIVIBRATOR

• Special-purpose oscillator
• Produces rectangular waveform
• Uses resistor and capacitor to set frequency

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MUTIVIBRATOR TYPES

• Monostable, one-shot
• Bistable, flip-flops
• Astable, free-running

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MONOSTABLE

• Produces rectangular pulse of fixed duration
• Uses a trigger input
• Does not run continuously
• Available in IC form

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MONOSTABLE

• States of Operation
• Resting Trigger-on
• Active Return

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ASTABLE

• RC type of circuit
• Generates a square or rectangular wave
• No stable state
• Free-running
• Available in IC form