Oscillators VTU syllabus 18EC42

1. Analog Circuits
18EC42
Module2-Lec4
Oscillators
Dr.Noorullah Shariff C
Prof & HOD(ECE)
SECAB Institute of Engineering and Technology
Vijayapura
Dr.Noorullah Shariff C 1

2. Introduction
• There are two different approaches for the
generation of sinusoids, most commonly used for
the standard waveforms:
• Employing a positive-feedback loop that consists an
amplifier and an RC or LC frequency-selective
network.
• It generates sine waves utilizing resonance phenomena, are
known as linear oscillators (circuits that generate square,
triangular, pulse waveforms are called non-linear oscillators
or function generators.)
• A sine wave is obtained by appropriate shaping a
triangular waveform.

3. Sinusoidal Oscillators
• A basic structure of a sinusoidal oscillator
consists of an amplifier and a frequency-
selective network connected in a positive-
feedback loop.
• For self-sustaining oscillations:
• the feedback signal must positive
• the overall gain must be equal to one (unity gain)

4. Sinusoidal Oscillators

5. Sinusoidal Oscillators

6. Sinusoidal Oscillators
• If the feedback signal is not positive or the gain is less
than one, then the oscillations will dampen out.
• If the overall gain is greater than one, then the
oscillator will eventually saturate.

7. Phase Shift Oscillators

8. Phase Shift Oscillators

10. LC Oscillators
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11. High-Q vs Low-Q

12. Colpitts Oscilllator

13. Hartley Oscillator

14. Crystal Oscillator

15. Crystal Oscillator

16. Crystal Oscillator

17. Series FET Crystal Oscillator

18. Parallel BJT Crystal Oscillator