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

Chapter 21

Oscillators

© 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.


Basic Oscillators

• Made up of:– Wave-producing circuit– Amplifier– Feedback circuit

• Cycle of voltage amplitude

• Cycle passes in one period


Sustaining Oscillation

• Regenerative feedback, or positive feedback

• Enough feedback voltage amplitude to replace energy lost


Armstrong Oscillators


Step One

• Current flows from B- to B+


Step Two

• First half-cycle of oscillation


Hartley Oscillators


Hartley Oscillators (Cont.)

• Used in radio receivers and transmitters

• More stable than Armstrong oscillators

• Radio frequency choke (RFC)

• Series fed oscillators

• Shunt fed oscillators


Shunt Fed Oscillators

• No dc path through coil L1 for emitter-collector current


Review

What is an oscillator?

Electronic circuit that generates an ac signal at a desired frequency


Review

What is a complete set of events in a repeated series called?

A cycle


Review

What differentiates a Hartley oscillator from other oscillators?

The tapped coil


Review

What are the two types of Hartley oscillators?

Series fed oscillators and shunt fed oscillators


Other Oscillators

• Colpitts oscillators

• Crystal controlled oscillators

• Power oscillators

• Operation amplifier oscillators


Colpitts Oscillators

• Similar to Hartley oscillators

• Split stator capacitor• Ganged capacitor


Crystal Controlled Oscillators

• Radio communications, broadcasting stations

• Piezoelectric effect


Crystal Controlled Oscillators (Cont.)

• Crystals control transmitter frequency

• Crystal ovens• Crystal added to

feedback circuit


Crystal Controlled Oscillators (Cont.)

• Crystal used instead of inductor in the tank circuit of Colpitts oscillator

• Pierce oscillators


Additional Uses for Crystals

• Two crystals producing two different frequencies for measuring temperature

• Timing devices• Signal generators


Power Oscillators

• Collector load of each transistor is primary of transformer

• Imbalance in conductivity starts oscillation


Op Amp Oscillators

• Crystal used in feedback circuit

• NAND gate starts op amp output


Wien Bridge Oscillators

• Use positive and negative feedback

• Balance of feedback in circuit crucial


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


Review

What is the distortion in a crystal caused by a voltage applied to the surface of a crystal?

Piezoelectric effect


Review

What is a Pierce oscillator?

A Colpitts oscillator that uses a crystal in place of the inductor in the tank circuit


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?

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

Documents

educational use

cycle slide

oscillators shunt

various oscillators

capacitor slide

feedback circuit slide

types of hartley oscillators

shunt fed oscillators