# 12-RC Phase shift Oscillator.pdf - Experiment No. 12 RC...

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Electronic Circuits Lab, Department of Electrical Engineering, College of Engineering Trivandrum1Experiment No. 12RC PHASE SHIFT OSCILLATOR USING BJTAIMTo design RC phase shift oscillator.THEORYAn oscillator is essentially a source of emf. Its output may be a sine wave, a squarewave, a triangular wave or a ramp. It is possible to vary the frequency and amplitude of theoutput. In this experiment we will be concerned only with sine wave oscillators.Feedback is said to existin an amplifier if a part of itsoutput is brought back into theinputcircuit.Considerthesituation in figure 1. A fractionβ(β< 1) of the outputVois broughtback into the input circuit.ThenetinputVitotheamplifier can then be written intwo different ways.isoVVV(1)whereVsis an external inputIn equation (1) the feedback is said to be positive. BothVsandβVodrive the inputterminal. So, this is positive feedback.If A is the voltage gain of the amplifier.oiVAV(2)From equation (1) and (2)osoVVVAHence gainArof the whole circuit including the feedback network is given by(1)osVAArVAThus, positive feedback increases the gain fromAtoAr. IfVs is reduced to 0 andVomade equal toVi, we get an amplifier that supplies its own input. An output voltage isobtained even in the absence of an external input. This happens when1A.An amplifier that supplies its own input is an oscillator. Then relation= 1 is calledBarkhausen criterion for oscillators. It implies thatβVomust have the same magnitude andthe same phase as the input. In general,Ais complex. This means that the output of anFig 1. Basic oscillator block diagram

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Term
Winter
Professor
Ankit Kaundal
Tags
Electronic oscillator, Sine wave, Electronic Circuits Lab, College of Engineering Trivandrum