How many RC stages are used in the RC phase shift oscillators?

Concept:

• The phase shift oscillator is a linear electronic oscillator that produces a sine wave output with a phase shift (Ideally 180°).
• It consists of an inverting amplifier element such as a transistor or op-amp with its output fed back to its input through a phase shift network consisting of resistors and capacitors in a ladder network.
• RC phase shift oscillator as shown in the figure is used to invert the input for a 180° phase difference.
• The single R-C network gives the 60° phase shift
• 180° is obtained by 3 RC sections to provide sustained oscillations. 
• The RC Phase shift Oscillator has a fixed frequency and is used at lower frequencies.

• For phase shift oscillator, the oscillating frequency is \(\omega = \frac{1}{{\sqrt 6 .RC}}\)