1. Electronic Circuit-II
Chapter 6

2. Topics in the Chapter 6 The Oscillator,
Feedback Oscillator Principles,
Oscillator with RC Feedback Circuits,
Oscillator with LC Feedback Circuits,
Relaxation Oscillators,
The 555 Timer As An Oscillator.

3. Oscillator definition
Oscillators are electronic circuits that generate an output signal without the necessity of an input signal.
They are used as signal sources in all sorts of applications.

5. Feedback Oscillator Principles

7. OSCILLATORS WITH RC FEEDBACK CIRCUITS
Three types of feedback oscillators that use RC circuits to produce sinusoidal outputs.
(1)The Wien-bridge oscillator,
(2)The phase-shift oscillator,
(3)The twin-T oscillator.
Generally, RC feedback oscillators are used for frequencies up to about 1 MHz
The Wien-bridge is by far the most widely used type of RC feedback oscillator for this range of frequencies.

8. The Wien-Bridge Oscillator

9. OSCILLATORS WITH LC FEEDBACK CIRCUITS
Although the RC feedback oscillators, particularly the Wien bridge, are generally suitable for frequencies up to about 1 MHz,
LC feedback elements are normally used in oscillators that require higher frequencies of oscillation.

10. Types of resonant LC feedback oscillators:
Colpitts oscillator.
Clapp oscillator,
Hartley, oscillator,
Armstrong oscillator,
And crystal-controlled oscillators.

11. The Colpitts Oscillator

12. The Clapp Oscillator

13. RELAXATION OSCILLATORS
The second major category of oscillators is the Relaxation oscillator.
Relaxation oscillators use an RC timing circuit and a device that changes states to generate a periodic
waveform.
Relaxation Oscillator are used to produce nonsinusoidal waveforms.

14. A Practical Triangular-Wave Oscillator

16. THE 555 TIMER AS AN OSCILLATOR
The use of the 555 timer as a voltage controlled oscillator (VCO)