Transcript Oscillators - CTAE Resource Network

Created by Jimmie Fouts
Houston County Career Academy
for
 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
 Oscillation: an effect that repeatedly and regularly
fluctuates about a mean value
 Oscillator: circuit that produces oscillation
 Characteristics: frequency, amplitude, distortion,
wave-shape, stability
 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
 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
 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 oscillation
 There is always some loss in the feedback circuit
 Amplifier gain must be greater than this loss
 Feedback 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
 Amplitude
 Frequency
 Waveform type
 Stability
 On 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 circuitry
 Output filter circuitry
 Amplifier gain, or
 Changes to input voltage
 May be sinusoidal (sine wave), square wave, or
triangular wave
 Sometimes referred to as a stable oscillator
 Source of a signal with consistent amplitude
 Source of a signal with consistent 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
 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