Q. Discuss the operation of a transistorized phase shift oscillator with the help of a diagram? Explain the phase shifting circuit?

An oscillator is a circuit which converts electric energy at d.c (zero frequency ) to electric energy at frequency varying from a few hertz to gigahertz . Stated simply , it is a source of alternating voltage or current . An electronic oscillator is, essentially, a feedback amplifier that supplies its own input i.e, it requires not external signal to initiate or maintain the energy conversion process.

The voltage divider R1-R2 provides DC emitter base bias, Re and Ce configuration provides temperature stability and prevent AC signal degeneration and collector resistor Rc controls the collector voltage. The oscillator output voltage is capacitively coupled to the load by Cc.

The phase shift circuit or the feedback network consists of three identical RC sections. Each RC section produces a phase shift of 600 .Therefore the net phase shift of the feedback network is 600 *3=1800 . The transistor amplifier produces a phase shift of 1800 .The total phase shift between the input and the output circuit is 3600 or 00 .

Hence the feedback is positive. The circuit is set into oscillations by any random or variation caused in the base current, that may be either due to noise inherent in the transistor or minor variation in voltage of DC power supply. This variation in base current is amplified in the collector circuit. The output of the amplifier is supplied to an RC feedback network.