Q. Explain the principle of transistor phase shift oscillator?

The phase shift oscillator consists of an inverting amplifier stage coupled to a three stage RC filter network. The network contributes a total of 180 degrees phase shift. With the 180 degree shift due to the inverting amplifier, the signal returned to the amplifier input is shifted 360 degrees. The R and C values for the network must be chosen so that the gain of the amplifier and network stages is unity. These are the necessary conditions for oscillation:

1. The phase shift through the amplifier and the network must be 360 degrees.

2. The magnitude of the gain of the amplifier and the feedback network must be one. (In practice try to make the gain slightly >1.)

Together these two condition are the Barkhausen Criterion or the necessary conditions for oscillation.