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.

What is LED. How LED works. Light Emitting Diode.

 One of the most common ways to generate light nowadays is by using a light emitting diode or led like the rest of the diodes as we saw in a previous lessons one of its characteristics is that it only allows the passage of electric current in one direction but we didn't talk about why they emit light so in this lesson we will see how an led works led lights have several features that make them one of the preferred options to illuminate such as having low energy consumption greater impact resistance and a longer lifespan and because of this they are available in many different formats but instead of going directly to analyze an led we will start reviewing how a common diode works because in theory these can also emit light it's just that they do it in an inefficient way if we have a circuit with a lamp and a power source energy will pass freely this is because electrons can move freely between metal atoms and when connected to the power source they are forced to move by adding a diode to the circuit and depending on its position the current can pass freely or be stopped and the reason why this happens is because of its composition inside the diode there is a semiconductor material such as silicon more specifically two types of this material if we took a piece of pure silicon and saw its atomic structure we will find that each atom has four valence electrons which are shared with the other four silicon atoms around it forming a crystalline structure with covalent bond that is they share their electrons so there are a total of eight valence electrons per atom resembling noble gases the most stable elements known to humankind if you don't like chemistry don't panic the important thing here is to understand that 80 electrons per atom is the magical number that keeps everything tightly connected in fact they are so connected that when a new electron wants to go through silicon the electrons that make it up cannot move hindering the flow of current however this can be changed through a process known as doping in which impurities are added to silicon to control its conductivity and convert it into a n-type or p-type semiconductor if we add impurities that have five valence electrons instead of four then we will have atoms with a total of nine electrons and since eight was our magic number we could say that one of the electrons will be left over or be freer than others which will allow it when connected to a power source to move and act as a conductor this alloy is known as n-type semiconductor because it has excess electrons which let's remember have a negative charge on the other hand if we do the doping with impurities that have three valence electrons we will have atoms with a total of seven electrons this means that we would have a gap allowing electrons to move through it and generating a movement of the gaps in the opposite direction since this alloy would have one less electron than its stable form it would have a positive charge and it would be called a p-type semiconductor moreover to simplify the visualization we will say that each hole corresponds to a positive charge this way when a pn junction is generated depending on the polarization of the voltage source there will be two possible results if the positive pole is connected to the n-type semiconductor and the negative pole is connected to the p-type semiconductor the holes and free electrons will move away preventing an electric current from being generated this case is known as reverse polarization on the other hand if we reverse the polarity of the voltage source the free electrons of the n-type semiconductor will be able to jump through the p-type semiconductor and close the circuit allowing the passage of the current this case is known as direct polarization and it is precisely here that the physical phenomenon that produces the emission of light occurs if we return to our visualization of the atomic structure and we focus exactly on the point in which the two semiconductors make contact we are going to find that electrons are being moved from an atom with more valence electrons to an atom with fewer valence electrons this is extremely important because this difference in the amount of valence electrons is also related to the amount of energy that they possess in other words an electron that is in an atom with five valence electrons has more energy than another electron in an atom with three valence electrons this means that every time an electron crosses this junction there is energy that is being lost but as the law of conservation of energy says energy cannot be created nor destroyed it can only be transformed and in this case the energy that the electrons lost when jumping from one atom to another became light or more specifically photons the fact that this happens at the atomic level has another implication since electrons move always from an atom a to an atom b the amount of energy transformed in each jump will be constant which in practical terms means that the emitted light will always have the same wavelength spectrum this also implies that by changing atoms a and b that is the impurities within semiconductors we can emit lights with different spectra referring specifically to the visible spectrum we can emit different light colors at this point we already know how the light is emitted but we still don't talk about why if this phenomenon occurs in a common semiconductor diode we don't see them shine continuously there are two main reasons the first one is that in many cases our eyes are unable to see the spectrum that is being emitted i couldn't find an exact demonstration of this but i did find a video in which a solar panel emits infrared light when applying a voltage and a diode generates a voltage by being enlightened all of which is related to the same phenomenon the second reason why a common diode does not shine is simply the shape if we think the light is being generated only at the points where the two semiconductors are in contact how are we going to see them if for the most part this area is being covered in this pattern in which they describe one of the first light emitting diodes the solution is extremely simple to move the semiconductors away from the connectors so that they do not cover the emitted light and reduce the thickness of one of them to such an extreme that light is able to pass through in a way we could say that this hasn't changed much to this day let's analyze an led from the inside out the first thing we will need is a substrate where we will put the rest of the materials to this we add a layer of n-type semiconductor and then another thinner p-type semiconductor layer the order is important because the transformation of energy occurs when reaching the latter layer then we add some cables so that the electric current can flow between the semiconductors and the light is emitted being extremely thin so it doesn't cover it technically only with this we already have a functional led but to be more efficient we will add a small reflector to direct the light which will be integrated in one of the electrodes and before covering everything in a transparent epoxy resin so that the set is more resistant we will add one last element a layer of phosphorus although this is used only in some cases such as white light in this particular case the diode is actually emitting a blue light which upon impact on the phosphorus layer causes this to emit a more yellow light the mixture of these two spectra is what generates the perception of seeing a white light the last thing i want to talk about is rgb diodes that can produce multiple colors although the truth is there is not much mystery left to it the rgb name refers to the colors that compose it red green and blue well indeed within this type of leds there are three pairs of semiconductors specifically selected to produce each color and by independently varying the voltage that passes through each of them the perception of different colors is generated i remind you that there are several more animations on my channel in case you want to check them out and also that you can support me in patreon to make more videos that is all for now and see you in the next episode.