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Oscillators

Oscillators. Jimmie Fouts Houston County Career Academy ENGR-AE-3. 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

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Oscillators

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  1. Oscillators Jimmie Fouts Houston County Career Academy ENGR-AE-3

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

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

  10. Output Characteristics • Amplitude • Frequency • Waveform type • Stability • On some oscillators, the capability to change frequency

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

  12. 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}

  13. 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

  14. Oscillator Stability • Sometimes referred to as a stable oscillator • Source of a signal with consistent amplitude • Source of a signal with consistent frequency

  15. 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

  16. 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

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

  18. Typical Uses of the Oscillator Radio and television stations require oscillators to develop the basic signal to transmit their information

  19. Typical Uses of the Oscillator Cell phones, electronic keyboards, and remote controls use oscillators to produce the required frequencies for operation

  20. 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

  21. 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

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