This is Anna Adamek in Vancouver, August 29th, 2017. Could you please give me your name and tell me where you were born? My name is William Devonport. People call me Bill. I was born in Breiland, British Columbia, which is about 200 kilometers north of Vancouver where we're recording. Could you talk a bit about your childhood? What were your interests when you were a child? I grew up in West Vancouver, which is a very secluded community. You had to cross two bridges to get to it, so it was very safe. And we were allowed to explore everywhere, and so I did mainly on bicycle. So exploring was one, cycling was another. I would say swimming. Because it's right on the ocean and then music. I was in a boys' band for many, many years and enjoyed that very much. And we traveled a lot within British Columbia, within Canada, and even to Europe. My conductor wanted me to be a musician, but turned out to be an engineer. Were your parents involved in science, or did they encourage you to pursue science? Well, my dad was working in a mine, a copper gold mine. It's a Britannia mine, which is just up the coast here. And then he was working at the little town I was born, which is a Breiland mine, so it was always kind of technical. And I always understood that I was going to go to UBC and started to be an engineer. That was my future. It's always turned out. Could you talk about your education? You mean the details, or the quality? Oh, yes, details. Where did you go to school? I went to school in West Vancouver. And there were two elementary schools at that time. One was Pollyburn, which is nearest to us. And the other one was Polly Johnson, which was named after a rather famous British Columbia painter. So those were two little schools. And I recently visited them. And then to West Vancouver High School, which was kind of old. When we started grade seven, we moved into temporary buildings because it was just after the war. People were moving in. And then they built a new high school for us up at the top of the hill, which was West Vancouver High, which was very high quality, I must say. Very high quality. And we'll talk about mentors later, and I'll tell you some of those teachers. And then, as they say, I was going to UBC and we'd go over every day over the landscape bridge up to UBC, carpooling, and my brother, John, joined me there the following year. So we all traveled together and it was very good, really, I thought. And I knew I wanted to be an engineering and I could have been chemical engineering, which my son is, or metallurgical engineering, which I am. So it was a very, very good education. And you chose to do your PhD at the Royal School of Mines in London, in England. Why there? Yes, yes. Well, of course, I graduated from UBC. I had my master's degree and I was working in New York and I decided I wanted to do a PhD. And for us at that time, we thought there were two choices. There was MIT, which was in Boston, and Imperial College in London, which is the Royal School of Mines. And I wanted to travel. I think that was maybe the main reason we got there. But there were also, there was kind of a route for Commonwealth students to come there. It was part of the Commonwealth Institute in London. And also there were two of my student colleagues from UBC who were there. And they, it was, it was no fee. And they got 500, 500 pounds a year. And my wife, my nephew, I was married before I went to New York. And so she came and she got about 400 pounds a year for working. So we had 900 pounds a year, which was just enough to get by. So it was very easy for us to get along. And there were a lot of Commonwealth students, a lot of English students. We had a fine time there. So how about your academic advisors? Is there someone who's already memorable? Well, could I go back one step to West Vancouver? So I don't know whether I would call him an advisor, but as a teacher, we had a rather lucky break. I was also studying, I was studying Latin. And there were six of us who wanted to do the advanced mathematics, but there was no class for us. So they put on a special class for six of us. And the teacher really taught us very well. And we taught ourselves, of course, with only six you could really teach yourself. So that was a really good thing. And before he died, I wrote to him and said how much he was important to my career because I still use algebra every day. What was his name? Mr. Kershaw. And he had an interesting, he was interesting because it would have been 1945 maybe, so the war had just ended. He was in Europe, and I think he was installing radar. He was an electrical engineer. And I think it was installing radar into airplanes. So they immediately moved towards the Pacific. The war ended before he got there, just as he arrived in Vancouver. And he got a job at teaching in West Vancouver. What did you consider your mentors? I'd see my, I'll start with perhaps my professors. I think Professor Williams at McGill University, I'm jumping. He wasn't, he was a colleague at McGill University. He was probably my main mentor from 1964 to 1981, the whole time I was in McGill. Now as teachers, Professor Bradshaw at Imperial College, I think he taught me, first of all, he taught me how to write. And what he did was, I would write something during the day that he would take it home and he would always have it read the next day. That really, really set me up for life. And I always did that as a professor. But my students whom I also taught that to, never did that. It took some, it took some dumps to get that kind of thing done. So Professor Bradshaw, I think those are the two that would really count. A professor degree from Toronto, he and I traveled together to Japan many times and he was also a mentor. Do you remember your first day at work? So much, actually. Now that you ask that, not so much. There was a UBC graduate there and he introduced me to the people. That part I don't remember. It was pretty young, I think. So after you graduated with your PhD in England you moved back to Canada immediately, or did you? Why did you move back? Well, to be honest, they wanted me to stay there in England. But we really yearned to get home. I think that's probably the real reason we wanted to come. And then I did have a job offer from McGill, which I got by serendipity while I was at Imperial College.  Closer to home, too. But I can remember my first day at McGill. Yes. So we arrived by ship. We sailed over the Strait of Belle Isle and came down through the St. Lawrence and landed at Montreal. And we were, my wife and I and the baby, who were just taking our time to go through customs and immigration. When Professor Williams came on and dragged us off, he said, Professor Downford has to get back up to the university. And he just took me up there and met all the faculty. And then we stayed with his family for maybe a week. And then found a little apartment at the university. So that was the first day. What was the culture like, research culture like at McGill at the time? Research culture. Well, it wasn't as advanced as it was at Imperial College. But it was really developing. And in that time period, late 60s, it really grew. And some marvelous came from Imperial College, probably at my recommendation, I suppose. Two others came. Could you give me the names? Rob Guthrie. Still there. And Phil Biston, who I just learned today, went away a couple of years ago. So, commitment to sustainable growth and research became very much more important. So what research did you conduct at McGill in those first years? 1960s. Sorry, I didn't quite hear that. What research did you conduct at McGill in 1960s? So when I got there, I really carried on my research and luck, which was really process research, particularly with regard to gas injection into metals and things like that. And then I moved into my own research, which was in Copper. And under Professor Williams' suggestion, you know, at Imperial College, we were kind of academic, at least. But I could see our students didn't really need that at McGill. They really needed some industrial aspects. So he suggested that I go out every summer, which was two or three months, to work in an industrial plant. So I did that. First of all, with Canadian copper fires in East Montreal. Then to the Gas Bay Copper, which was so in the Gas Bay, and it was a smelter, copper smelter. Then Canadian Electric Living Zinc, which is just west of Smelter Yellow. Finally to once with mining and smelting in Belle Dune. Tell operations in Quebec, done in French or in English? Well, it was all English in those days. But not in Bellyfield, not so much in Bellyfield. But so Canadian copper fires, I think it was just changing. And there were a huge number of workers. It wasn't very automated. And they were, I guess, the heavy workers who were large, were immigrants. I remember. But it was... See, it was mainly English. So there was no problem communicating? Same was true in Belle Dune. I think there was a little more French in Belle Dune. But they're recently in Al-Tawfiq. So I think I could communicate. How long were you at McGill? 17 years. So I started my research. The first research I'm best known for is probably copper refining, copper electro-winning, copper smelting. But I did some other research on aluminum production I was trying to work on and vacuum purification. I worked on those. Let's see. I think that's about all. But I started writing my books then, too. That was the other thing. I started... I did a sabbatical half-year in Queensland. I spent a year there. I met their Professor Biswas. I should call him another mentor. Now that I think that Professor Biswas is in the University of Queensland. And so I had the opportunity there to visit all the medical operations in Australia pretty well off. So... And I visited several copper ones. So I spoke to Camille and said, perhaps we should write a book on this subject. We did it starting in 1971. I'm finishing in 1976. So that was how I got... So I would say he was the mentor as far as getting books published. And I noticed that your books deal with theoretical approaches but also practice. So did you work with industries at this time, too? Could you talk a bit more about that approach, I think, to audience practice? Yes, yes. Well, I would say one of the things I did actually all my life was visit industrial plants. And maybe averaging about 12 a year. I just enjoyed doing that. So when you say work with industrial plants, certainly I had students that were working in there and their colleagues, if I had an industrial question, I would go and visit the plant. And I would go all over Canada, Quebec and Ontario, Manitoba, and just go on here. And then also in the United States, Georgia, and there's all those copper-making places. So I certainly had access to everything I needed to know in industry. When did you decide to move to the University of Arizona and why? I moved in 1981. By that time, I was working on flash furnace copper smelting. And although it was one in Canada, it was at the Sudbury and Kinko Sudbury, we were building six in Arizona, not in Arizona, but Arizona, New Mexico, and Utah. So I went down there to be at the center of that industry. And like with going to McGill, I got a letter from Arizona saying, please come down and be the head of my department. Be the head of our department. So I did that. Did you find any differences or similarities between the two universities? Well, McGill is an international university, which gave it a certain flavor. Arizona, though, at that time was an institution that was supposed to educate the children of taxpayers. They had a very narrow objective. But while I was there, I would say it changed into a research one university in the States, with a large, huge space program, quite a large material science program, and a big hospital of its own, so it really did change into a research institution. I guess under the pressure of funding, more than anything, but it became really quite active and surprising to me. I think it wasn't a research one to start with because you needed air conditioning. A lot of those buildings didn't have air conditioning. That's an interesting point.  So could you tell me what that involves? Well, as I interpreted, it starts on the left, you might say, with geology, and what we might call oral genesis, how ores are formed, then geology, then geological engineering, then mining engineer, mine development, mineral processing or beneficiation, and smelting. One was smelting sulfur dioxide control, and then radiation and smelting and environmental control, that's what I look at, and then refining and, I'd say, purificate or quality control, quality control, that's the way I look at it. I was always thought of as the expert on smelting and refining, but I moved quite a bit towards geology and oral genesis. I just began to think those were keys to obtaining metals from ores. So that's more or less how I think about it. What other areas did you research? What other areas of research at the University of Arizona? Well, I stayed with copper smelting and copper refining, but a new field developed actually in Arizona and it's solvent extraction, purification, which involves leaching oxide ores, or then oxide ores and calcicide, and you get an impure liquid and with an organic solvent, you extract pure copper from that solution and then electric it in from there. So there was a lot of work going on with different solvents, how best to do it. So frankly, I got into the, in on the bottom floor when that started because we had the very first one in Arizona, very first one, maybe the first two, there's a tie between the second one, one was in Zambia and one was in Arizona. So I just took on that field then and I wouldn't say they became an expert, but an expert in the application. So that moved in that direction. You have a number of patents. What are your intentions? Well, I'll have a couple of patents. I wouldn't say they've been adopted very much. One was we were trying to, you know, it's a difficult process or a very energy intensive process. So we were looking to find a temperature process. And one of my students, Guido, had an idea how to do that and it was using solvents of various kinds. And so we were trying to use that to get low energy production of aluminum. And we got good plating and we were making good aluminum, but the solvents weren't very stable. So I thought that from the end of that one, really. The other one was with several people, with Henry Solomon de Friedberg, who I'm going to be meeting, and Ralph Harris, first of all, on vacuum purification of steel. The vapor pressure of the impurity is particularly copper.  And copper at steel is a deadly impurity. You can see that you just can't use it. And it worked pretty well. I went and visited several plants. I went to visit a plant in Buffalo in New York to see how it would work. And although it would work, industrially it would have been a little hard to adopt. So as a man at that time, I was leaving Guido. And he went on with that piece of Ralph. Is there a set of innovations or an innovation that you are especially proud of? No, I think it's... I think it's mainly my books. Some are just descriptive, like copper. It's right over here, copper. The iron glass furnace I built in 1979, and the person I was having lunch with had read it and has a copy. If you took a theoretical look at it, that process, glass furnace melting, was built in France. So as the very last lecture I got in steel making at UBC, had what they called the Rhysdiac. And it was clear that none of us understood it, but I don't think the professor understood it either. So that was 1959. So in 1970, maybe 1976, after I finished the copper book, I said, why don't I have a look at that? And so I went to it from the basics and developed the whole theory. I could explain what the graphical approach actually meant, and I could get an equation for each of the lines. He told me if you added oxygen, what it would do. If you increased the temperature of the glass, what it would do and their lines would all shift and I could predict why. But the interesting thing with that book, it was quite interesting because it had to have points on the graphs. And some of them I couldn't figure out. But many nights I would wake up and I would have an equation for that point. And it would always be wrong. And I would let it down. And finally I did wake up and it was right. So it was kind of a serendipity way of that book. So I went on from there. And I think it was still in print. So it was part of that. And then I did the same with flash smelting. I think it opened some eyes on kind of the whole way this kind of smelting went with flash smelting, which is oxidation of fine sulfide particles from flotation. So we could predict what the rate of the product should be as compared to how much oxygen you put in or how much heat you put in. Some people consider that my best book. It might be. What was the most difficult project that you worked on? One that didn't go off too well. One that was maybe the most dysfunctional that you would consider a failure. Oh well. I was writing a book on uranium. And I had two or three co-authors. But I was the only one that did any writing. And I understand it because as a professor you can do what you want or whatever's missed. And they were working, and they just couldn't get it together. In fact, it's at the side of one of the potential co-authors for lunch. And he's quite sad about it. But I said I don't know. He just got a move on. I just moved on right away. So it was a little difficult. So that actually leads me to the next question. How do you see the difference between the research culture in academia and within the industry? Well, the beauty of research at a university is how free you are. Your limitations are quite a bit less. You also have very young students, malleable students maybe. So I like those aspects. I kind of like the aspects of university. You could work, you could work as much as you wanted. And I was always like that. When I first went to work and people were only working eight hours a day, it just didn't feel right for me. So that's probably where I became an academic. It's become a little more difficult because funding is harder to get. But I work very closely. For example, in Montreal, there was a research center very closely with those people. A number of my students were in there. And they all did well under that kind of work. And now I'm working with people from Hatch, in Burlington, and likewise. It's nice to be working with people that are related to the industry. And some of those, two of those people are investmentists also. Every day kind of thing. Who are your most memorable students? Well, Guido Capuano, who I referred to, he was a mature student. I think he had escaped from Italy right after the war or something like that and came to Canada. And he was a big, gruff guy. And he had many ideas, many ideas. Many good chemical ideas. In fact, he was the, at least that year, he had what I would call the best dissertation of anyone when he graduated. But unfortunately, he was also interested in money. And so he was always worried about trying to sell this. And I just couldn't quite agree with him on that. So he was an exceptional student. Now, a second one was Matt King. He was now in Perth, Australia. And we worked together on sulfuric acid. So I need to discuss with you a little bit. Now, if you have a sulfide, or you're going to produce some sulfide, it's some form. And most of it is going into sulfuric acid, which is a marketable problem. But nobody really knew how the process worked. And so Matt and I developed, let's say, a matrix, a matrix algebra approach to it and equilibrium approach to it. I worked all that out and eventually we could tell the industry how they should arrange their processes. And I'm really quite proud of that. And Matt was a wonderful student, too. He was another best. He had the best what we call preliminary exam that the year he was doing that. So he was a very good author. Were there many women involved in the future that you were? Not too many. Too many. We were closely with two, all of us at Arizona. See if I can remember. Sandy Fowler, who was a very good student. We worked on the sulfide extraction, as I described. But she ended up, after her master's degree, she's a material specialist for helicopters. So she moved away on something else. And the other one was Chris Combo. She didn't become an environmental engineer with several cooperation, but I really enjoyed working with those people. I read that another area of your expertise is the application of thermodynamics and process engineering principles to extractive metallurgy processes. Could you explain this? Well, I think so. Again, I'll revert back to the sulfuric acid. We actually did develop a thermodynamic equilibrium equation for that process, which is really one of the steps in making the sulfuric acid is oxidize SO2, 2-3, and essentially you dissolve the SO3 in water and make sulfuric acid. It's a little more complicated, but that's the general principle. So we developed this thermodynamic equation based on algebra. I can really go back to Mr. Kershaw and say, you know, that's how I could figure that out. And then we could tell what should be done with the amount of air that one used in the process of oxygen.  So we determined how you could avoid that and yet get high efficiency of SO2 oxidation. So it's hard to describe. I'll just try and describe it. We have an equation which we developed and we have matrix algebra and we work the two together. And I think that's kind of unique. What is your fondest memory that relates to your work? See, you know, I might have just described it to you. You know, I might really have done, that was the most unique thing. And in this equilibrium equation, we just came out of an algebra that I re-taught and I really can't say too much more than that. That was the thing I really enjoyed. That would be a problem. What are your thoughts on innovation culture in Canada today, in the past and today? Well, not having lived here for a while, I'm not sure, but I've been talking to people here and they do seem to be doing a lot of things that the one I sat beside today, he's now stationed in Germany and he's applying things that he learned here in Canada. And we sat with another one that's a company here and I was surprised. They really developed it here. They developed one of the problems is, what they said to me, British Columbia is the most costly manufacturing region of the world. They might be pretty close to. FIA was able to locate suppliers around the world and started the business here and now markets throughout the world as well. It seems to be in pretty good shape from what I've just learned here. And how did the academic culture change throughout your career? Well, I'd say one thing, you don't rank on the board anymore. That's a good change. I don't know if it's a good one, but it's a good change. There's a lot more techniques for it. Of course, distance learning. And now the students get the following notes before the course electronically. So those things have all changed. And I'm not sure that I was completely prepared for that. And it would have taken quite a lot of effort to do that, but I was nearing retirement so I kind of figured that out. But of course that was already the old. And did the relationship between academia and industries change within your career? No, I kept up visiting plants until maybe two or three years ago. So, you know, I would go to a conference in Germany. I would then visit three or four German plants. I had opportunities to go to South Africa to visit all their Titanum. I haven't seen them, but maybe that's another thing I'm quite proud of. One of the books I wrote was Extract and Emergency of Nickel Cobalt and Titanium Blue Metals. Now nobody puts them together, even though in the periodic table they're arranged together. So I managed to do that. So I'm quite proud of that. I haven't received any comments from a book, so I don't know how good that is, but I think that was pretty good fun. So I was still trying to do the same things. And still today trying to do the same things I did maybe in 1967 or something like that. So not too much. I'm thinking about closure of certain research centers like Noranda, Alkan in Kingston. Did this have an impact on academics? I think there are not as many as there used to be, as far as I can see. I was talking to somebody today about uranium and I think their research center has recently closed down. So perhaps not as much as it once was. I'm kind of guessing on that. And what are your views on innovations that come out of metallurgical industries today? Well, the talk at lunch today, it's an innovation that I could see happening. It was happening when I was at UBC, it was Professor Frank Forward who was working on pressure leaching, oxygen pressure leaching. And the plan is in Fort Saskatchewan, Alberta. I think it's still called Sherrod Gordon. And they really started this whole field of leaching of sulphide orbs and even leaching of oxide orbs. That's been a major contribution by Canadian research both at Ottawa, at UBC, at Fort Saskatchewan. That's a very big success. Yeah, with a new plant in Madagascar. Did the changes in maybe social perceptions such as, for example, environmental movement had any impact on your work? Well, I became very interested in the environment when I started to write price melting because that was one of the things it could do. It was in a think-efficient capture system for capturing SO2. You know, prior to that, when I first came here, when I first went to McGill, I was visiting these smelters and they were just horrible. All the SO2 was just going into the atmosphere and we got acid writing and all that kind of stuff. And the flash smelting was one way to get out of that because it smelled of particulates with oxygen or preheated air or oxygen enriched air and that gas could be captured and made into the sulfuric acid very efficiently. And so that did kind of dominate my work for a while and then I saw sulfuric acid writing exactly the same thing. So those were the objectives of those books. When I told you it's geology and so on and the smelting and then environment, that's really what I mean. So I devoted a lot of time to that and I'm devoting my time now to carbon footprint with the book for writing on the last furnace. So I would say I devoted my later years in part to that field and I think with some success. That's very interesting.  I believe you have your own consulting practice now so what would be your advice to a young student of metallurgy? Just starting the career. Well, enjoy your work. Maybe that's the first thing. If you are enjoying it, look for something else. I'd say look to the future. What are the innovations going to be? What can you contribute? Both in the way of purity and environment, safety. I'm working with two young men now. It must be in the 25. Try to think of their work as romantic. Is that possible? You know, I have some feeling towards it but I think they do. That's what I would say. And one thing in working for Hatch, they get young students called them interns that we're using now. So we get four month interns since I've been working with three of them and the other ones arrive. So I can encourage them to enjoy it, especially enjoy your work and I hope you will go through my book and solve your problems. Are there any events that you throughout your career that you noticed that we must study? We really have to understand. To understand the field of metallurgy. I think that's probably more into the field of alloy development and the one thing I did with the rare earthwork was, again, I visited plants all over the world. But I visited one of those catalyst factories and that's where they make the alloys the capture and inclusion for the automobile. So I think looking for that kind of catalysts, anything that will help the environment, and visited a magnet factory with the rare earthwork using magnets, a very powerful magnet, I guess. I don't know whether you've heard of it. So I learned a lot about that and I watched one being made and oriented. So working on improving those kind of things. There's the other one. Magnets, catalysts. I forgot what the third one is. Batteries. Oh, there you go. Batteries. That's a big one. I can see batteries as a real goal because the trouble with wind electricity and solar electricity can't do it when the wind drops or when the night comes that you need to be able to store it. So I think those magnet batteries are very interesting. I worked on rare earth batteries which are very good but lithium batteries because of their lightness and their storage capacity are much better than you. I think that's really an attraction right now. So it was interesting to get in involved in all of those things and the magnets are used for, you know, you might have 200 magnets in your car and they're very powerful and the smaller they are, the better they are. So research and preparation. I think every handbag has one. Oh, I see, I can see. They had everywhere. Oh, I see, yeah. What are you proudest of in your life? Don't just work, but your life. Do I work? Well, I think in spite of all I've talked to you about my family is certainly my everything. I can tell you right now my son is in Houston and all the flooding has gone out. So I was a little worried about that while he seems to be in a dry ground. So I would say family was really everything and everything. If that's in good shape I would work in whatever house I'm in. So your wife traveled quite a bit with you? Yes, she did. Did she work or what did you do? I went to school teacher. She also went to UBC and she went to normal school in Victoria. I guess this is the normal school we invited to college, I guess. She worked, she taught I'm going to Rhyman and then she taught trailblazer. That's part of the thing maybe I should just go back to my earlier life. The real advantage I had as a young man was I had summer jobs. Of course, we always. So I worked in Fish and Marine. I worked in sawmill. I worked in the forests and I worked two years in Comenco. Consolidated mining and smelting as we call it in those days in trail. So even when I left school I had an industrial background. That was very helpful. I lost a bit of it while I was at Imperial College. Anyway, to go on, she was teaching at trail and that's where we met. So we got married a year after being in trail. She was teaching there and then she taught a year after a year after we married and then she was going to teach in England but she was advised not to do that. So she worked as a clerk for eight pounds a week. Is there anything you would like to add? No, I think well I would say traveling the world that was such a good part of my life and brought on by this my career really. So I traveled virtually everywhere. The only place I didn't go was Russia. I went there as a tourist but not as a metallurgist which I was sorry about because there were things I would like to see. I even traveled to Poland to Brasov and Katowice. And Nitsa Krogov all those copper places. So virtually everywhere except Russia. Kazakhstan So I wonder from your travels did you see was there something that was really striking about differences in countries or maybe similarities when it comes to the field to metallurgy? Well I think if I may say the Soviet system really held things back a bit because they were told what they had to do. But other than that everywhere I have to speak highly of Germany wonderful, wonderful industry workers wear ties to Japan likewise. I've spent quite a long time in Japan and I've enjoyed that of going back next month to about after so but even there you know what I observed was you wouldn't think we had the same sense of humor but when you see something without any dialogue I was laughing at the same place everybody else was so I think people must be nervous Well thank you very much for being there You're welcome


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.