How RC Phase Shift Oscillator works? Complete working with circuit

Basic Principle: The RC Phase shift oscillator uses common emitter configuration i.e. CE configuration of transistor. It produces 180° phase shift in addition to the phase shift of 180° by the transistor. So we get total 360° phase shift to produce positive feedback.

Working: When supply is connected to the circuit, the base current of T₁ suddenly increases. This change is amplified by T₁ to produce negative feedback of 180° to the phase shift network.

The phase shift network also produces another 180° phase shift. So the total phase shift is 360° i.e. the input and output signals are in-phase.

Since transistor T₁ is used as amplifier, the circuit produces sustained oscillations. The output frequency of the circuit is given by the following formula:

Where,
R = resistor in phase shift network in ohms
C = capacitor in phase shift network in Farad

Advantages & Disadvantages

1. It is a simple circuit using RC network.
2. Very low frequency from 1Hz to 300 kHz can be obtained.
3. It can be fabricated in integrated circuit form.
4. Frequency stability is excellent.
5. However, we cannot control frequency easily.
6. This circuit is not suitable to produce high frequencies in radio frequency range.