Q. What is the basic principle of oscillation in an RC phase shift oscillator. With a neat sketch explain its working?

For producing oscillations there must have positive feedback. Positive feedback occurs only when the feedback voltage is in phase with the original input signal. This condition can be achieved in two ways. Take a part of the output of a single staged amplifier(giving a phase shift of 180⁰ ) and then pass it through a phase shift network giving an additional phase shift of 180⁰ . thus a total phase shift of 180⁰+ 180⁰ = 360⁰
(which is equivalent to a phase shift of 00 ) occurs, as the signal passes through the amplifier and the phase shift network. This is the principle of a phase shift oscillator.