The phase shift network in this circuit, consists of three RC sections.
The phase-shift oscillator circuit consists of a single transistor amplifier section and a RC phase-shift network. The constructional details and operation of a phase-shift oscillator circuit are as given below. The oscillator circuit that produces a sine wave using a phase-shift network is called as a Phase-shift oscillator circuit. Consequently, a total phase shift of 180 o is produced, i.e., voltage V 2 leads the voltage V 1 by 180 o. The following circuit diagram shows the three sections of the RC network.Įach section produces a phase shift of 60 o. Therefore, in practice, R is varied to such a value that makes V 1’ to lead V 1 by 60 o. However, adjusting R to zero would be impracticable, because it would lead to no voltage across R. If R were reduced to zero, V 1’ will lead the V 1 by 90 o i.e., ɸ o = 90 o. The output voltage V 1’ across the resistor R leads the input voltage applied input V 1 by some phase angle ɸ o. The following circuit diagram shows a single section of an RC network. The phase angle by which it leads is determined by the value of RC components used in the circuit. We know that the output voltage of an RC circuit for a sinewave input leads the input voltage. These are also called as Phase–shift Oscillators. Hence the need for RC oscillator circuits arise. As well, the circuit becomes neither bulky nor expensive.Īll the drawbacks of LC oscillator circuits are thus eliminated in RC oscillator circuits. These oscillators can also produce lower frequencies. By doing so, the frequency stability is improved and a good quality waveform is obtained. We have another type of oscillator circuits, which are made by replacing the inductors with resistors.
Though they have few applications, the LC circuits have few drawbacks such as We have observed that the LC combination in oscillators provide 180 o phase shift and transistor in CE configuration provide 180° phase shift to make a total of 360 o phase shift so that it would make a zero difference in phase. The oscillator circuits discussed so far has employed inductor (L) and capacitor (C) combination, in the tank circuit or frequency determining circuit. One of the important features of an oscillator is that the feedback energy applied should be in correct phase to the tank circuit.
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