Created by Jimmie Fouts Houston County Career Academy for.
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Transcript of 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
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