 Hello, welcome to the session on impedance coupled amplifier. At the end of session students will be able to explain the operation of impedance coupled amplifier as well as they can analyze the various parameters of impedance coupled amplifier like input impedance, output impedance and through that the voltage gain of each stage and the overall voltage gain contains are like this. Here in this video we will also see the comparison between all the coupling schemes. Here one stage of the amplifier is coupled to the next stage of the amplifier with the help of inductor. As we are conducting inductor to the collector circuit that is in between VCC and the collector terminal of transistor. Therefore, it gives the isolation that is as you know the load inductor or as the inductor will block the AC signal. So, it will be providing the minimum resistance path for the DCs. Therefore, VCC will be available at the collector as we are connecting the inductor. So, here load inductors are most effective at the high frequencies because the inductance coil increases with the frequency as the inductance of coil. How it is so? As you know XL equal to omega L. Therefore, these are not widely used for the audio amplifiers because it gives the impedance for this audio amplifier as the inductor is connected between the VCC and the collector. Frequency response is good for the high frequency values. So, look at the circuit diagram of impedance coupled amplifier where voltage divider biasing is used R1, R2, RA is used and bypass capacitor CE is also used over here. So, when you bypass the capacitor properly you will find the bypass of the noise signal. When you are correcting the coupling capacitor over here it also gives the proper isolation and DC biasing conditions will be maintained. So, you will be passing the AC signal and it will block the DC at this stage. Same way input capacitor and the output capacitor provides the same working over here. Voltage divider biasing provides the stabilization of Q point and that is maintained in the further stages as we are using the coupling capacitor for the prevention of further DC signal. Therefore, biasing conditions will be maintained over here. Register RL is connected between collector and the ground. You can observe in the previous stage that is precedence stages we are using inductor at the collector stage, but when you are at the final stage then register RC is used in place of inductor. So, the amplitude of the signal or the output voltage depends on the inductive reactance that is at the collector over here. So, this is applicable for all the stages. Further the load inductors are most effective at the high frequencies because XL equal to omega L. So, you can observe in the circuit diagram it provides the DC over here and you are transferring the AC signal to the next stage that is base of the next stage and when value of frequency is larger then value of XL will be also large. Therefore, you will give or you will get the larger gain over here larger gain over here. So, coupling capacitor will provide the couples a signal between the stages as well as it will block the DC signal and it is not used for audio frequencies due to the connection of inductor at the collector stage. So, this is what we have regarding the impedance coupled amplifier that is we have the voltage divider biasing as well as we are going to give the proper gain at the high frequency signal over here. So, when I convert this diagram into my equivalent figure that is transistor is replaced by its HRE model then it gives the circuit which contains the inductor in parallel with the next stage of R1 and R2 and as while simplifying the circuit I am making the shot between the VCCN ground at that time this R1 and R2 in the circuit will become parallel to each other. In the same way I have the value of RB which is multiplication of beta times RE2 that is equivalent value of this transistor circuit or base circuit. Therefore, we have this figure which shows the equivalent diagram for the impedance coupled amplifier that is resistor R1 and R2 are in parallel with the beta 1 RE2 dash R1 dash this is for first stage and for the next stage it is L in parallel with R1, R2 and beta 2 RE2 dash. So, we have this equivalent circuit. So, while calculating gain always we are going to find the individual voltage gain and then overall voltage gain. Therefore, if I concentrate on the AV2 that is my final stage of the multistage amplifier that is AV2 equal to RC parallel RL upon RE2 dash. So, this is at the collector end RC parallel RL upon RE2 dash. If I assume the voltage gain at the first stage then it will be again giving me the parallel combination of XL with R1 parallel R2 parallel beta 2 RE2 dash where XL is the impedance at the collector stage and R1 R2 and beta 2 are the second stage resistance as well as equivalent resistance value for the transistor. So, in this way I can also assume here or I know that when value of XL is very very large as compared to R1 R2 and beta 2 RE2 dash parallel combination since when we go for the parallel combination as the equation is R1 R2 by R1 plus R2. Therefore, the approximate value of XL will be very large as compared to other values. Therefore, we are neglecting XL. See as this is a parallel combination we are neglecting XL, but if it was in the series combination at that time XL will be there and all other component will be vanished. As we know that XL is multiplied with the other terms divided by XL is added with the other terms. So, as XL is larger other terms will be cancelled at the time XL will get cancelled and so proper or the effective value of the impedance will be R1 parallel R2 parallel with beta 2 RE2 dash. So, in this way I will get the voltage gain for first stage and the second stage and the overall voltage gain is the multiplication of both. Now, so this is the analysis of the impedance coupled amplifier and as you know the advantage is like it is suitable for the high frequencies and not for the lower frequencies. Therefore, I will now compare the various coupling schemes for the multistage amplifier. So, see the table over here and find out which particular application do you want and accordingly select the proper coupling scheme. For example, I will say I have to block the DC signal at that time I will use the RCN transformer coupling, but if I do not want to block the DC signal at that time I should not use direct coupling over here where no any element is corrected for the coupling. Now, the impedance matching is achieved in the transformer coupling rather than the RC coupling and the direct coupling. So, here whenever you want the application of impedance matching that is at the input stage and the output stage you have to use transformer over there while for the low frequency amplification or for the DC signal amplification you have to use direct coupling. While the RC coupling provides the very good frequency response, but it will drop at the lower frequencies because we have the drop of due to the capacitor that is coupling capacitors. So, there is low frequency response is reduced here the frequency response is not so good for any values because varies it will vary with the help of resonant frequency and in the direct coupling will get the very good frequency response over all the frequencies, but it will be affected due to the stray capacitors at the higher frequency end. Now, just pause the video and find or just complete the entry in the table yes and the DC amplification is possible only in the direct coupling. So, these are the various coupling schemes and we have seen the impedance coupling where it is suitable for the higher frequencies. So, that is also the very good solution over the RC coupling or the transformer coupling. These are the references. Thank you.