1. Created by Jimmie Fouts Houston County Career Academy for
Oscillators
Created by Jimmie Fouts
Houston County Career Academy
for

2. Objectives 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

3. Word Wall
Oscillation: an effect that repeatedly and regularly fluctuates about a mean value
Oscillator: circuit that produces oscillation
Characteristics: frequency, amplitude, distortion, wave-shape, stability

4. Overview of the Oscillator
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

5. Amplifiers as Oscillators?
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

6. Electrical Feedback
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

7. Feedback and Amplifier Gain Conditions for Oscillation
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

8. In-phase Feedback
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

9. Input Characteristics
Steady source of direct current (DC)
In many applications, the DC source requires a filter

10. Output Characteristics
Amplitude
Frequency
Waveform type
Stability
On some oscillators, the capability to change frequency

11. Oscillator Amplitude
Usually determined by the gain available from the amplifier
Supply voltage and circuit losses affect amplitude

12. Oscillator Frequency
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}

13. Waveform Type 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

14. Oscillator Stability Sometimes referred to as a stable oscillator
Source of a signal with consistent amplitude
Source of a signal with consistent frequency

15. Ability to Change 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

16. VFO
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

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

18. Typical Uses of the Oscillator
Radio and television stations require oscillators to develop the basic signal to transmit their information

19. Typical Uses of the Oscillator
Cell phones, electronic keyboards, and remote controls use oscillators to produce the required frequencies for operation

20. 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

21. 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