Oscillators

Created by Jimmie Fouts

Houston County Career Academy

for

Define the basic oscillator circuitIdentify elements of feedback in the oscillatorIdentify the conditions for oscillation to

occurIdentify input and output characteristicsIdentify the difference between VFO and VCO

oscillatorsIdentify common uses of the oscillator

Oscillation: an effect that repeatedly and regularly fluctuates about a mean value

Oscillator: circuit that produces oscillationCharacteristics: frequency, amplitude,

distortion, wave-shape, stability

One of the basic building blocks of electronicsInput is a direct current (DC) power sourceOutput is alternating current (AC)Can generate sub-audible frequencies or very

high frequenciesMost oscillators are amplifiers with feedback

Most amplifiers will oscillate when conditions are correctExample: 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

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

Feedback alone does not promise oscillationThere is always some loss in the feedback

circuitAmplifier gain must be greater than this

lossFeedback must be in-phase

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

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

a filter

AmplitudeFrequencyWaveform typeStabilityOn some oscillators, the capability to change

frequency

Usually determined by the gain available from the amplifier

Supply voltage and circuit losses affect amplitude

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}

Generally, determined by: Feedback circuitryOutput filter circuitryAmplifier gain, orChanges to input voltage

May be sinusoidal (sine wave), square wave, or triangular wave

Sometimes referred to as a stable oscillatorSource of a signal with consistent amplitudeSource of a signal with consistent frequency

Oscillators sometimes have the ability to change frequencies

Crystal oscillator frequency is controlled by changing the crystalCrystals are usually cut from quartz to

generate a specified frequency when operating

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

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

Typical Uses of the Oscillator

Radio and

television stations

require

oscillators to

develop the basic

signal to transmit

their information

Typical Uses of the Oscillator

Cell phones,

electronic

keyboards, and

remote controls

use oscillators to

produce the

required

frequencies for

operation

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

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