What is oscillator. How oscillator works. Types and kinds of oscillators. Crystal oscillator.

 

hey friends welcome to the Blog all about electronics in this video we will talk about the electronic oscillator and we will learn about the basic working principle of the oscillator now the electronic oscillators are used in wide range of applications they are used in laptop and smartphone processors for generating the clock signals while they are used in the radio and mobile receivers for generating the local carrier frequency and even they are used in the single donators which is used in the lab to test the circuits so this oscillator accepts the DC voltage and it generates the periodic a signal of the desired frequency now the oscillators can generate the frequencies from few hurts to even gigahertz now the output of the oscillator can be either a sinusoidal signal or a nine sinusoidal signal like a square wave and the triangular wave now in simple dumps this oscillator circuit is nothing but the amplifier which is given a positive feedback so let us understand the working principle of this oscillator so let's say some input sinusoidal signal is applied to this amplifier so at the output the input signal will get multiplied by the gain of this amplifier and the output signal will be equal to a times the input signal now let's say this output signal is given as a input to the feedback circuit now usually the feedback circuit used to be a frequency selective circuit or the resonant circuit and let's say and the output of this feedback circuit is equal to VF so VF can be written as beta times output voltage and that is equal to beta times input voltage where hear this beta is nothing but the feedback fraction and it defines what fraction of the output voltage is given as a feedback to the input stage now if the phase shift that is introduced by this amplifier in the feedback circuit is zero in that case this feedback signal will be in phase with the input signal now let's say this phase signal is getting added to the input signal and at the same time the input signal is removed from the circuit so now this feedback signal VF will act as a input for this amplifier so after removing the input voltage whether we will get the sustained oscillations or not that depends upon the product of this a and beta and it is known as the loop gain of the oscillator so if this loop gain a beta is less than 1 in that case or the period of time the input signal will die out so now let's say in one particular circuit a beta is equal to 0.9 and in this circuit the input voltage V in is equal to 2 volt of sine wave so now whenever this input signal passes through this amplifier on the feedback circuit then input signal V in will become 2 volt multiplied by the 0.9 that is equal to 1 point 8 volt and once again whenever this input signal passes through this loop then the input signal will get reduced by the factor of 0.9 so in this way every time this input signal passes through this loop the amplitude of the input signal will reduce in over the period of time the oscillations in the circuit will die out similarly whenever a beta is greater than 1 at that time the oscillations in the circuit will build up so as you can see in both cases we are not getting the sustained oscillations and that is only possible whenever a beta is equal to 1 so when a beta is equal to 1 at that time the feedback signal VF will be same as the input signal provided the input signal and the feedback signal have a same phase so in that case we will consistent oscillations at the output so in oscillator to get the sustained oscillations two conditions should get satisfied the first is the product of this a beta should be equal to 1 in the second is the phase shift of this loop gain should be equal to 0 meaning that whenever the input signal travels through this amplifier in the feedback circuit the overall phase shift that is introduced by the circuit should be equal to 0 and these two criterias are known as the barkoff sense criteria for the halation now a so far we have assumed that whenever this oscillator is switched on at that time some finite amount of starting molted is applied to this oscillator but actually if you see no signal is applied to this oscillator and still we are getting the oscillations at the output so the question is how is it possible how we can get the oscillations at the output without giving any input to this oscillator so the answer is the thermal noise is present in every circuit and if you are aware this thermal noise contains all frequency components starting from a few Hertz to even hundreds of gigahertz so initially whenever this oscillator is turned on all the frequency components of this thermal noise will get amplified by the amplifier and the amplified output of this thermal noise will be given as input to the feedback circuit now like I said earlier this feedback circuit is the frequency selective circuit so out of the all the frequency components only for a one particular frequency the phase shift that is introduced by this amplifier in the feedback circuit will be equal to zero while all the frequencies will have a different phase so from the all other frequencies only one particular frequency will get added with the input noise and in this oscillator circuit initially the loop gain a beta is slightly set more than one and because of that the noise signal of particular frequency will get build up over the period of time and once the signal reaches certain voltage at that time the loop gain of the circuit will become one and it is possible because of the nonlinear behavior of the either amplifier or the feedback circuit so in this way the noise signal of the desired frequency will get build up over the period of time and once the signal which is finite voltage then the loop gain of the circuit will become one and in this way it is possible to get the sustained oscillations at the output so this is the basic working principle of the oscillator now earlier we had seen that two criterias for the sustained oscillations and these two criterias can also be proved mathematically so let's say the output of the feedback circuit is equal to VF and this signal VF will get added with the input signal supposing the input signal is present at that time the input to the amplifier will be equal to V in plus VF and at the output we will get a times V in plus VF now here VF is nothing but beta times output voltage so if you put the value of this VF then V out will be equal to a times V in plus a beta times V out and if we simplified then we can say that V out by V in is equal to a divided by 1 minus a beta now here in the oscillator we are not providing any sort of input signal and still we are getting the oscillations it means that a beta in the circuit should be equal to 1 so that this condition will get fulfilled so from this we can say that the magnitude of this loop gain should be equal to 1 and the phase shift that is introduced by this loop gain should be equal to 0 so in this way mathematically these two criterias can also be proved now like I said before in oscillators the feedback circuit used to be a frequency selective circuit so this feedback circuit can be made up of either RL RC or RL C components and even the quartz crystal can be used for the frequency selection so depending upon the type of feedback circuit the oscillator can be classified as either RC he'll see your crystal oscillator and moreover that depending upon the arrangement of these components these oscillators can be classified further now the oscillators which is mentioned over here are the sinusoidal oscillators or even it is known as the harmonic oscillators because the output of these oscillators used to be a sine wave while some other oscillators also provides a different kind of shapes like square wave and the triangular wave and these oscillators are known as the relaxation oscillators and this type of relaxation oscillators can be build up using either open or the time arises like 3 timer and we will see the design of the different types of oscillators in the future videos so I hope in this video you understood the basic working principle of the oscillator so if you have any question or suggestion do let me know in the comment section below if you like this video hit the like button and subscribe to the channel for more such lessons.