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Chapter 21 Oscillators. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain what occurs during an.

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Presentation on theme: "Chapter 21 Oscillators. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain what occurs during an."— Presentation transcript:

1 Chapter 21 Oscillators

2 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain what occurs during an oscillation cycle. Identify various oscillators. Discuss and compare the Armstrong oscillator and the Hartley oscillator. Outline the operation of the crystal oscillator and the power oscillator.

3 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Basic OscillatorsOscillators Made up of: –Wave-producing circuit –Amplifier –Feedback circuit Cycle of voltage amplitudeCycle Cycle passes in one period period

4 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Sustaining Oscillation Regenerative feedback, or positive feedbackRegenerative feedbackpositive feedback Enough feedback voltage amplitude to replace energy lost

5 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Armstrong Oscillators

6 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Step One Current flows from B- to B+

7 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Step Two First half-cycle of oscillation

8 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Hartley Oscillators

9 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Hartley Oscillators (Cont.) Used in radio receivers and transmitters More stable than Armstrong oscillators Radio frequency choke (RFC) Series fed oscillators Shunt fed oscillators

10 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Shunt Fed Oscillators No dc path through coil L 1 for emitter- collector current

11 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is an oscillator? Electronic circuit that generates an ac signal at a desired frequency

12 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a complete set of events in a repeated series called? A cycle

13 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What differentiates a Hartley oscillator from other oscillators? The tapped coil

14 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are the two types of Hartley oscillators? Series fed oscillators and shunt fed oscillators

15 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Other Oscillators Colpitts oscillators Crystal controlled oscillators Power oscillators Operation amplifier oscillators

16 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Colpitts Oscillators Similar to Hartley oscillators Split stator capacitor Ganged capacitor

17 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Crystal Controlled Oscillators Radio communications, broadcasting stations Piezoelectric effect

18 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Crystal Controlled Oscillators (Cont.) Crystals control transmitter frequency Crystal ovens Crystal added to feedback circuit

19 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Crystal Controlled Oscillators (Cont.) Crystal used instead of inductor in the tank circuit of Colpitts oscillator Pierce oscillators

20 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Additional Uses for Crystals Two crystals producing two different frequencies for measuring temperature Timing devices Signal generators

21 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Power Oscillators Collector load of each transistor is primary of transformer Imbalance in conductivity starts oscillation

22 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Op Amp Oscillators Crystal used in feedback circuit NAND gate starts op amp output

23 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Wien Bridge Oscillators Use positive and negative feedback Balance of feedback in circuit crucial

24 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Radio Detection and Ranging (Radar) Existence of electromagnetic waves that travel at the speed of light Advances occurred prior to World War II Microwaves are transmitted out of radar dish in energy pulses When waves strike reflective material, some is reflected back Types of radar –Pulsar radar –Continuous-wave radar –Doppler radar –FM radar Some planes are invisible to radar –Stealth bombers –Stealth fighters

25 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is the distortion in a crystal caused by a voltage applied to the surface of a crystal? Piezoelectric effect

26 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a Pierce oscillator? A Colpitts oscillator that uses a crystal in place of the inductor in the tank circuit

27 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. For Discussion Compare and contrast an electronic oscillator and a clock pendulum. Explain the operation of a Hartley oscillator. Why are crystal oscillators used in many commercial transmitters?

28 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Armstrong oscillator –An inductive feedback oscillator. Colpitts oscillator –A basic type of oscillator characterized by tapped capacitors in the tank circuit.

29 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Crystal controlled oscillator –Circuit with a stable high frequency, used in radio communications and broadcasting stations. Crystal oven –Maintains a constant temperature of crystals used to control transmitter frequency.

30 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Cycle –1. Set of events occurring in sequence. 2. One complete reversal of an alternating current from positive to negative and back to the starting point. Ganged capacitor –Two capacitors controlled by a single shaft.

31 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Hartley oscillator –A basic type of oscillator that has a tapped oscillator coil. Oscillator –An electron tube generator of alternating current voltages. Period –Time for one complete cycle.

32 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Pierce oscillator –Type of Colpitts oscillator in which a crystal is used in place of the inductor in the tank circuit. Piezoelectric effect –Property in which certain crystalline substances change shape when an emf is impressed upon a crystal. The action is also reversible.

33 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Positive feedback –Energy fed back to the tuned circuit. Also called regenerative feedback. Power oscillator –Oscillator that uses the collector load of the transistors as primary and the ac output at the secondary.

34 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Regenerative feedback –Feedback in phase with the input signal so it adds to the input. Series fed oscillator –Oscillator in which the inductor is in series with the transistor collector circuit.

35 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Shunt fed oscillator –Oscillator whose dc path for the emitter- collector is not through the inductor, causing two current components to separate and take parallel paths. Signal generator –An electronic oscillator that generates various signals for testing.


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