Conditions for Sustained Oscillations:

To produce sustained oscillations in a typical tank circuit, the following conditions must be met:

1. Energy Compensation: The amount of energy supplied must compensate for the losses in the tank circuit and match the energy drawn by the load.
2. Frequency Match: The applied energy should be of the same frequency as that of the natural oscillations in the tank circuit.
3. Positive Feedback: The amplified energy must be in phase with the existing oscillations, i.e., positive feedback should exist within the amplifier loop.

Classification of Oscillators:

Oscillators can be classified based on the method of feedback and frequency range as follows:

$$if\:R_1=R_2=R_3=R;\:and$$

$$C_1=C_2=C_3;\:then$$

$$frequency\:of\:oscillation;\:f_{o}=\frac{1}{2\pi RC\sqrt6}$$

Phase Shift Oscillator (Using RC Network):

• A Phase Shift Oscillator uses a single transistor amplifier along with a RC phase shift network.
• The transistor amplifier provides a 180° phase shift, and the RC network provides another 180° phase shift, resulting in a total 360° phase shift (or 0° net phase difference).
• This ensures positive feedback, which is a key requirement for sustained oscillations.

Advantages:

• No need for inductors or transformers.
• Capable of producing very low frequencies.
• Provides good frequency stability.

Disadvantage:

• Suitable only for low power output applications.