RC Phase Shift Oscillator

• It consists of a conventional single transistor amplifier and a RC phase shift circuit. The RC phase shift circuit consists of three sections R₁C_1, R₂C₂, and R₃C₃.At some particular frequency f₀ the phase shift in each RC section is 60⁰ so that the total phase shift produced by the RC network is 180⁰. The frequency of oscillation is given by

• When the circuit is switched ON it produces oscillations of frequency determined by equation 1. The output E_O of the amplifier is feedback to RC feedback network. This network produces a phase shift of 180⁰ and the transistor gives another 180⁰ shift. Thereby total phase shift of the output signal when fed back is 360⁰

Merits-

1. They do not require any transformer or inductor thereby reduce the cost.
2. They are quite useful in the low frequency range where tank circuit oscillators   cannot be used.
3. They provide constant output and good frequency stability.

Demerits –

1. It is difficult to start oscillations.
2. The circuit requires a large number of components.
3. They cannot generate high frequencies and are unstable as variable frequency generators.