 Hello, and welcome. I am Sachin R. Gengze, Professor and Head, Department of Electronics Engineering at Walchen Institute of Technology, Sulapur. In today's lecture, we will have an introduction to oscillators, which are, we are going to talk about the oscillators which are designed using operational amplifiers. The learning outcomes of this session, after completing this session, you, that is, student will be able to explain the different types of oscillator and explain working of oscillators in general. So, what is an oscillator? An oscillator, a function of the oscillator is to generate alternating current or voltage waveform. So, the output of the oscillator circuit is either a waveform, which is alternating current or alternating voltage. One can define oscillator also as the circuit that generates repetitive waveform of fixed amplitude and fixed frequency without any external input. So, if you look at the output of the oscillator, it is a waveform which is repeated and it has a fixed decided amplitude and the frequency which is also fixed. Now, one may ask a question, how it is possible to generate any output without any external input? Definitely, it is not possible. For the oscillator circuit, we are connecting DC supply as a power supply and then that DC power supply is getting or rather the power from the DC power supply is getting converted into alternating current AC signal. As we know, the oscillators are very much used in various electronic devices ranging from simple clock generator in which we require oscillator to sophisticated digital instrument, maybe instrument like calculators and complex computer in peripherals also we require oscillator. Common example of signal generated by oscillator include signal broadcast by radio and television transmitter. We know that for generating the carrier frequency we require oscillators. Also, the clock signal that regulate computers and cars clock and the sound produced by electronic beepers and video games, all these kind of circuits, all these kind of electronic circuit that requires oscillator insight. If you look at the types of the oscillator, the oscillators can be classified based upon what are the types of the component or what are the components used to design the oscillator or what is the frequency that is generated by the oscillator or what are the type of the waveform generator. See, it is although the oscillators which are generating sinusoidal waveforms are quite common but there can be requirement or there are oscillators which are generating non sinusoidal repeated waveforms, maybe a square wave or triangular wave or a sawtooth wave, all these are we are calling them as an oscillator. So, the oscillator can either be classified based upon component use or what kind of frequency it generates or what is the type of the waveform that is being generated by the oscillator. Based upon the components used by the oscillator there are three type of the oscillator, the oscillators which uses RC that is resistor and capacitor or LC that is inductor and capacitor and then there can be crystal oscillator also. Based on the frequency of the oscillation generated or the frequency of the waveform generated, the oscillators can be classified as a low frequency oscillator or audio frequency oscillator or radio frequency or high frequency oscillator. And as I said there are number of different types of the waveforms which can be generated like there can be sinusoidal which is of course very popular type of oscillator or there can be square wave or triangular wave or sawtooth wave or any other repeated waveform being generated by the oscillators. The low frequency oscillator is an electronic circuit that generates a frequency below approximately 20 hertz. So, it is a very low frequency even below of 20 hertz and these oscillators are used for or they are being used these kind of terms they are typically used in the field of audio synthesizers to separate from an audio frequency oscillator. And then other type of oscillator which is very popular is called as an audio oscillator which is producing the waveforms which are having frequency in the audio range that is from 16 hertz up to 20 kilo hertz. And lastly there are oscillators which are generating high frequency or the radio frequencies and a typical application of that as a carrier waveform in different type of modulation. And then these oscillators are generating RF which are in the range of 100 kilo hertz to 100 kilo hertz all these are coming under oscillators. Then based upon the component one of the very popular type of the oscillators are RC oscillators. In an RC oscillator the filter is a network which is there in an oscillator which is which is designed using resistors and a capacitor. RC oscillators are simple to design and RC oscillators are mostly used to generate low frequencies say for example in the audio range. We have seen that the audio range is something between we have seen that it is between 16 hertz to 20 kilo hertz. So mostly these audio oscillators are generated using R and C. Common type of RC oscillator circuit are phase shift oscillator and wind bridge oscillator. So different types of even in an RC oscillator or a low frequency oscillator there are different methods to design the oscillator. Two of the popular methods of oscillator design are the phase shift oscillator and wind bridge oscillator. So here I leave you with a question that please think and answer what are the types and what are the applications of the oscillators. Okay I think that you must have now ready with the answer what are the types of the oscillator we have seen that there are three types of the oscillator depending on the components used depending on the frequency generated and depending upon the type of waveform generated and then what are the applications of the oscillator we have discussed various applications of the oscillators. Let us move ahead with the concept of oscillators. Now what is an oscillator? Basically oscillator is a amplifier with a feedback where the part of the output of the amplifier is a feedback to input via what is called as the feedback circuit. If the signal which is feedback from output to input through feedback circuit is of proper magnitude and phase then circuit produces oscillations and we know that most of the oscillator uses what is called as the positive feedback. So look at the look at the oscillator how it can be you can see that oscillator has two parts first is an amplifier let us assume that the gain of the amplifier is AV then there is a feedback circuit and the feedback factor for this feedback circuit is B. Now initially I can assume that there is a noise in the circuit which acts as an input for the amplifier so amplifier produces the output the part of the amplifier is feedback and added please see that it's a positive feedback so added again to the input of the amplifier amplifier then produces still more output higher output then again it is feedback and added and likewise initially at t is equal to 0 I can assume that there is some input which is a form of noise but once I that input is given or I assume that that input is given to the oscillator circuit then the oscillators start producing the output which is a sinusoidal waveform without any input but please remember without any input not possible to generate any output there is a DC power supply which is there for the amplifier and then from that we produce the output which is a sinusoidal signal. So when we talk about the oscillator it consists of two part the first one is an amplifier with a feedback as you can see the output of the amplifier is taken let us assume that the output of the amplifier is V0 then it is feedback through a feedback circuit which is having a feedback factor of beta so the output of the feedback output of the feedback circuit is Vf which is a part of the V0 please understand this V0 multiplied by beta will give me Vf then Vf is again feedback and then again some output is being produced. So the oscillator necessarily consists of two part the amplifier with a feedback definitely whose gain is Av greater than 1 and then there is a feedback circuit okay now what are the conditions for oscillations now in this circuit what are the conditions for the oscillation the first condition there are two condition which must be made the first condition is that the magnitude of the loop gain the total gain of this is again of the amplifier Av multiplied by the feedback factor beta so the total loop gain Av B or Av beta must be at least equal to 1 and then the total phase shift of the loop gain Av B must be equal to 0 degree or 360 degree so that indicate that it's a positive feedback where the power supply of the amplifier is switched on initially electronic noise as I say in the circuit provides a non-zero signal and then the oscillation start the type of the waveform generated by the oscillator depend upon the component used and then it may be sinusoidal square or the triangular so with that we come to the end of the lecture introduction to oscillator the references I have used for rather I have used only one reference for this and that is op-amps and linear integrated circuit by Ramakan Kaikwan so with that I leave you today thank you very much for attending the lecture thank you