Shortcuts Steps for Problems on Negative Feedback - Electronic Devices and Circuits

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click the Bell icon to get latest videos from Ekeeda Hello friends now here in the chapter number 5 we are on the step of the numericals of negative feedback circuits so before that we'll have to learn the steps to follow the numericals based on feedback amplifiers so we will follow these steps once we follow these steps with feedback without feedback to find out input resistance output resistance all the stuff related with their amplifiers and some tricky problems we'll be discussing in the next videos so for that we require these important steps so let's start with the steps to follow for the numericals of negative feedback amplifier let's start with the step number 1 so first of all step number 1 is nothing but the identification of the feedback topology so in the circuit circuit can be like anything for example if your voltage divider by a C amplifier is given so how you can identify that whether it is a first of all whether it is with feedback or without feedback and then we'll have to understand that if it is with feedback then what kind of topology that we have to use right then and only then we can get get that whether the input impedance is increasing or decreasing output impedance is decreasing or increasing so based on the sampling and mixing part we'll get to know that this is which feedback topology right so feedback topology will have to understand by just knowing the fact that key at the output side whether voltage is sampled or current is sample that means whether it is shunt a circuit or series circuit if it is shunt a circuit then I can say that it's nothing but de volt is sampling if it is a series circuit then I can say that it's nothing but your current circuit so very simple trick that I'll give you later on but right now we will learn particular circuit related to this feedback amplifiers so if at output shunt circuit then I can say that it's nothing but voltage sampling I'm specifying focusing more on sampling and mixing part this is because once you get bit sampling and which mixing we can easily relate that particular topology with sampling and mixing part so here I will say if at the output shunt circuit then it is a voltage sampling if it is a series circuit then I can say that it's nothing but your current sampling okay now simply at the output if at input similarly I will write if it is shunt circuit then it's a shunt mixing right if it is series circuit then it sir series mixing okay I will tell you after this particular video what are the other nama current for this voltage series voltage and current series and currents a shunt as well okay so once you identify this feedback topology we will have to move further to solve the numerical for required findings okay one thing that you have to understand very carefully take to identify he went back topology no understand see if sampling done at output terminal that means if I'm saying a complete voltage divider bias ze amplifier is there and from the output node I have one resistance which is connected at the input side right so I can say that that will be your voltage sampling okay so I can say that it's nothing but your voltage sampling if sampling is done a deed directly at the output terminal so right so whatever sampling I will be getting that is nothing but voltage sampling right so we'll take an example we'll say this is particular circuit okay hey if I have taken this sample from here right this is our feedback and here only my output is there right so I can say that this is nothing but D type of feedback we're sampling is is voltage sampling so if it is voltage sampling this is very very simple now to understand the feedback topology right now in another case I can say that if I have this is the voltage and if I'm taking the feedback from this particular resistance RF okay so I can say that this is nothing but sampling is current sampling it's not a voltage so obviously it will be current a sampling sampling is of current sampling right so this is the first method that we have to understand for the trick okay as a trick and the second one is about mixing right if feedback is directly connected to maze for gate terminal right this is only related with the this trick is only related with the fe t + BJT amplifier so if I am using the open then that will not be done for this particular trick okay so this is for Fe T and BJT amplifiers okay in your syllabus only BJT and at 50 amplifiers will be there for negative feedback so if feedback is directly connected to the base or gate terminal then I can say that it will be a shunt mixing ok otherwise it will be these series mixing we will take few examples later on further after this particular video we will learn the complete analysis related to each and every topologies okay so if feedback is directly connected to the base and gate terminal Fe t bj for Fe T BJT amplifier if it will be shunt mixing otherwise it will be series mixing okay now we will again take few examples where we'll get to know that suppose here I have taken this sample no matter what sampling is I want to take the mixing part and this is the input and I have connected this complete feedback RF feedback circuit directly to base so this will be your shunt mixing ok so this I will name it as shunt mixing okay in another sense I can say if this is your RF okay whether it is let's say this is your output voltage okay so output voltage is there so this is your feedback circuit RF resistance and this feedback is not directly connected to the base or gate brother it is connected with vs rather I can also say that mathematically vs is now equal to this v i+ this VF okay so it's nothing but you are series mixing so we have got some tricks for that particular amplifiers to identify what is the feedback topology that is nothing but your step number one so let's move towards the step number two that is nothing but to draw the circuit without feedback circuit without feedback bravi circuit without feedback we must know which particular feedback topology I am using okay so for this we have to draw we have to do some short circuit we have to do some open circuit so keep this in mind that I will draw the general diagram again I don't want the circuit big feedback okay I bought it without feedback okay so what should I do if the circuit is there itself but if it should not be avoided then I can say that I will convert this into your feedback so again and then we will analyze what is nothing but your value of I what is nothing but the value of a what is nothing but the value of O and then later on we will divide it by your D sensitivity factor that is one plus a be very simple now not let's see this is the B okay let's take an example of voltage series negative feedback in voltage series for put in series insane for voltage series output pay what will be your circuit circuit is shunda an input pain your circuit is series so this is shunt series right so if I am saying I don't want this feedback right I have to convert my this particular remaining amplifier circuit at the input side as well as output side so to have the good side of the amplifier without feedback then what will have to do will have to short this shunt connection that means we have to short the output voltage so its result is short output voltage this is only for the case of voltage sampling now to have the output side right to have the output side what I will do I don't want this feedback at the input side right so I do I want to eliminate that if it is series connection then I can say that if I open that particular circuit between your series direction of feedback and your mixer then I can say that it will be very sufficient to have discipline without feedback if I open it right so I will do the open circuit input right this is only example if I am say voltage series right so open it I will say let's short it connected to the wrong okay so if I shot it then I will get at the input side okay so output pitch change the time so mu J input form to make it either input pitch change the line to measure output form the negative tonight right that all for our topology we will write that complete thing in your topic tabulated form right this complete thing you will write in a tabulated form such as let's say that feedback topology number one number two number three and number four right I will write in short that is voltage series voltage shunt 4sh right current series and current shunt okay first of all we would like that which is sampling and which is mixing okay so this is what it's ugly this is also voltage sampling this is current sampling and this is current something right moreover and right if it is voltage sampling then I have to write it as shunt connection this is shunt connection this is series connection and this is series connection okay simple now what we'll have to learn that what change I have to make at the input side and what change I have to make it at the output side so we will write this as for input for input side we have to change the output side right so output we will do whenever it is shunt and we'll say that output voltage short circuited right here also output is short circuited here is a open circuit and output because it is in series if I don't want a feedback then we can say that if I open one of these series connection if I open that circuit then I will disconnect between back so it related to your amplifier circuit without feedback so here also I will say it is open circuit and right similarly what we will do at the output side as this is series connection I will write this first as series connection this is the shunt connection this is the series connection and this is its solution connection then I can say that this is voltage series this is voltage shunt resistance series at least current shunt okay very nice so wherever you look as series we have two pointer right so what change I have to make this is changed for output side of these without feedback circuit this is nothing but if it is serious I will say that output you don't have to change the output you rather you have to change the input side so open circuit and input right similarly for the shunt we have two short circuit at the short circuit at input similarly as it is a series I mean right it as open circuit at input and here it will be short circuit at input right we will take few example a very simple example that we will be taking as example this is the circuit and this is the input signal that I am getting very thick okay simple and now we will say that here it is your feedback okay this is your RF this is an e1 this is our E - this is our c2 and this is our c1 right no matter well what is your DC voltage here we are considering your all AC analysis right so with this is big feedback circuit this is given something right this is given circuit big feedback now we have to draw without feedback right so we will draw without feedback circuit without feedback totally socket without filter what do we do first of all we have to identify the topology as this is your output voltage that is been given and this is your input voltage I am saying that output feedback is taken from the output node right so it is nothing but your voltage sampling right here I can say that as feedback taken from output node right it is nothing but your voltage some simple and now your feedback is taken at directly at the base so I can say that here it is your shunned amazing okay this is trying to mixing voltage sampling so your feedback topologies voltage shunt a negative feedback so this topology is voltage okay now we will say that for voltage shunt what we'll have to do for the input side and output side so for voltage shunt if you want to develop this particular input side then what we'll have to do we'll have to open D we'll have to do the output as short-circuit right so as this is the voltage and I say that you are output should get short-circuited if i short circuit this output this are f at the input side will be down there right so I can say that acting could say what we will do this is your vs right yeah and I can say this is your RF not right this will be your left and I can say that now this is nothing but the change at the input side so change at input okay the rest all the things we have to get as it is occurrence this particular input side is consider now we will not change the rest part we will give this cut as it is this will be our key only this is your rc1 and this is attached to your further I want to develop your output part so that's why I have kept it as it is so do the non-resident despot RC bun and these are Eva okay now what we'll have to do it is the voltage shunt the negative feedback so what we'll have to do we all have to do the same thing that is nothing but it's a voltage shunt a negative feedback so we can say that short circuit at the input side as well so what you can do we will do the short circuit at the input side will consider this vs is equal to zero so if we keep this vs is equal to zero then I can say that this RF will be grounded right so if this RF is grounded so I can say this will be in but a little bit you are seen to as far as AC analysis is considered okay so this is also and this is also RF both are f we have to keep in our circuit right so I can say that this is nothing but your change handy output so far whatever we have gotten it is nothing but the feedback resistance RF is placed at the input side as well as output side nearly same as that of your Millers capacitor assemblers effect okay but we are not jumping into this Miller effect but you have to concentrate that particular theory for developing here the input side and output side without feedback circuit once we get this without feedback circuits will move a tail for this step number three fine we find a and find our I and find our oh that is nothing but the required parameter right once we get these this is nothing but gain without feedback this is gain without feedback he is a feedback factor that will be different for different topology you have to keep this in mind I am oh right once you get that I and carpeau we will have to calculate the value of RI f and Oh F and F as well so I will write this here yep all this and office le divided by 1 plus AV right so calculate B calculate a once you calculate both these values you will easily get the value of a right then what we will have to calculate i right I will be related with our I multiplied by 1 plus a B or our I divided by this is RI f it's a feedback with feedback 1 plus so this is depends on depending on type of topology the same case what uh-oh I will not repeat it again Oh F will have to again calculate with the same way right so in short once you get the value of a B or a and alpha we can easily calculate all the values of the parameter required for the negative feedback amplifier obviously big feedbacks so we will summarize this completely video with three steps to solve the numerical space from the negative feedback amplifier first step is to identify the negative feedback topology based on the sampling and based on mixing right next step is to draw the complete circuit without feedback to develop input side what change you have to make at the output side to develop at the output side what change you have to make at the input side so depending on that we can develop the circuit without feedback and the third step is to calculate all the mathematical calculation is be a I Oh and etcetera etcetera depending on the application depending on the numerical which comes for you right so we will stop this particular with this particular findings we will stop here next video we will learn few new miracles which has scaled for the Mumbai University thank you so much for watching this for dinner video and we will look more and already see will keep it up riyo's thank you so much you

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Shortcuts Steps for Problems on Negative Feedback - Electronic Devices and Circuits

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