 And welcome to the video lecture on Oscillators Using Operational Amplifier Part 1. At the end of this session, students will be able to describe the working principle of oscillator and they will be able to describe the working of RC phase shift oscillator. So, before moving towards the concept, you have to know about basics of OPAM that is IC741. So, let us see first what is mean by oscillators. Oscillator is a circuit which generates the repetitive waveforms of fixed amplitude and frequency without providing any external input. There are number of uses of these oscillators like different applications for example, the electronic devices like laptop and mobiles use this oscillator to generate the clock signal. It can be used in many receivers that mobile or TV receiver to generate the local carrier frequencies and it is also used in signal generators to generate the different kinds of sinusoidal and non sinusoidal waveforms. So, let us see about this oscillator working principle. So, oscillator is a type of feedback amplifier in which the positive feedback signal is given at the input from the output. Block diagram of oscillator is consist of the amplifier, let us say its gain is A v and the second block is of feedback circuit with the feedback factor beta. Now, we will consider v in is the input voltage, v d is the differential voltage, v o is the output voltage and v f is the feedback voltage. So, according to this diagram, we can write the equation for differential voltage as v d is equal to v in plus v f that is input voltage plus feedback voltage. Then we can write the equation for output as v o v out is equal to A v into v d, then the next equation for feedback we can write v f is equal to beta into v out and we will take the ratio of output and input that is v o upon v in is equal to A v upon 1 minus A v beta. But it is a oscillator, so we cannot give any external input here, there is no requirement of any external input. So, the v in is equal to 0, still it is giving some output voltage there. So, we will consider v in is equal to 0 and v out is some non-zero quantity. Now, putting these values in the above equation, we will get A v beta is equal to 1, it can be expressed in polar form as A v beta is equal to 1 and the phase angle or phase shift is 0 degree or 360 degree. So, in any kind of oscillator to obtain the sustained waveform oscillations, we have to satisfy two points which are called as the Barkhausen's criteria. So, the criteria is the magnitude of the loop gain that is A v beta must be at least 1 means the loop gain should be unity and the second is total phase shift in the loop must be equal to 0 degree or 360 degree. The oscillators can be categorized into two types, the first type is sinusoidal and second is non-sinusoidal. Basically, if the amplifier provides 180 degree phase shift, then the feedback circuit should provide the another 180 degree phase shift to make the condition satisfied that the total phase shift should be 0 degree and 360 degree or 360 degree. So in sinusoidal oscillators, it will generally produce the sine or cosine waves and non-sinusoidal oscillator generally produce the waves like square, triangular, south tooth etc. Output of the oscillator depends on the components used in that circuit as well as the oscillation at the output depends on the components used in the feedback circuit. So, there is no any input voltage externally provided. So what will be the input voltage basically is the circuit's noise itself means initially the input is taken from the circuit noise as we provide the input supply. So, let us see about one of the sinusoidal oscillator which is nothing but the R C phase shift oscillator. So, we will draw the circuit for R C phase shift oscillator yes. So, first according to the oscillator block diagram, it is the amplifier circuit and it is the feedback circuit. So, for this amplifier circuit we will use operational amplifier that is IC 741. So let us draw first the opamp circuit pin number 2 that is inverting terminal, pin number 3 is non-inverting terminal. So, we will provide the supply voltages plus 12 volt minus 12 volt it is at pin number 7 and it is at pin number 4. Now pin number 6 is the output voltage we will consider it as a V o this is R in and this is R f that is feedback resistor. So, I will use this opamp in inverting amplifier mode. We have satisfied the amplifier circuit in the oscillator now we have to design the feedback circuit in the oscillator design. We have to connect some circuit as a feedback from output and from output to input I will extend this. So, this is the feedback circuit consist of R and C components so it is called as the R C phase shift oscillator. So, here it is feedback circuit and it is the amplifier circuit which is inverting amplifier. Circuit should work on the principle of Barkhausen's criteria. So, it should satisfy the two conditions. First is it should take the overall phase shift as 0 degree or 360 degree and the loop gain must be equal to what these two conditions should be satisfied here. So, we will see the first condition of phase angle now as it is inverting amplifier it will give us 180 degree phase shift. So, the remaining 180 degree phase shift should be obtained from this feedback circuit. So, how it is obtained we will see one consider this is single R C stage. So, theoretically we can consider it will give the phase shift of 0 degree to 90 degree. So, theoretically we will consider the maximum phase shift which is given by the single R C stage. To get the 180 degree we can just use the two R C stages in the circuit instead of three R C stages. But the practical problem is that if we have to use these two R C stages then it is considered that it is giving 90 degree phase shift. So, the value of R is nearly equal to 0 and due to this typically gain will be 0 for this feedback circuit and it is not satisfying the criteria. So, we will use the three R C stages in the feedback circuit. So, single R C stage will give the output with nearly 60 degree phase shift. The output is leading 60 degree because R C circuit is nothing but the phase lead circuit. Now we have to use the three R C stages in the feedback circuit. So, here we can consider each stage will give 60 degree phase shift. So, after this 180 degree phase shift 60, 60 and 60 will provide us the total 180 degree phase shift and this total will produce the 0 degree or 360 degree phase shift. Practical circuit will not provide 60 degree at each stage, but the overall circuit will give us 180 degree phase shift. So, it will fulfill the first condition of Barkhausen's criteria that is the total phase shift is of 0 degree or 360 degree. Now, we have to see about the second condition. According to the calculation we will get the attenuation of 29 means here beta can be written as 1 by 29 and here we have to choose the value of R f and R in such that the gain must be equal to 29 because A v into beta is equal to 1. So, here the gain is considered to be 29 and accordingly we can design R f upon R 1. So, we will consider the mod value of R f, R f upon R 1 is equal to 29. So, accordingly we can design the values of R f and R in sorry is equal to 29. Now, these two conditions are satisfied at the particular frequencies it is called as f0. So, f0 is nothing but the frequency of oscillation and the frequency of oscillation can be given as 1 by 2 pi root 6 into R c. It is for 3 stage R c network. So, it is the frequency of oscillation which will give us the sustained oscillation output. This R c phase shift oscillator can be used in low frequency ranges nearly 5 hertz to 1 megahertz and it is mostly used in audio frequency range applications. These are the references. Thank you.