lec23 (41).pdf - Microwave Integrated Circuits Professor...

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Microwave Integrated Circuits. Professor Jayanta Mukherhee. Department of Electrical Engineering. Indian Institute of Technology Bombay. Lecture -23. Impedance Matching Circuits for Amplifiers. Welcome to another module of this course microwave integrated circuits, we are now in week 6 of this course, so far all the circuits that we had considered were basically passive circuits. So, passive circuits are one which do not produce or circuits where the output power or rather I should say passive circuits are the ones which do not require external power supply whatever power they need for their operation come from the input itself. So they do not need an external DC source for their operation. Then the active circuits are ones which for their operation separately need a power supply it can be a DC bias circuit or it can be directly device can be directly connected to power supply. Now active circuits, some common examples of these active circuits are amplifiers, mixers and various other active circuits that are used. So when active circuits, when we are considering active circuits for microwave engineering, there is often the problem of impedance matching i.e. we make a device but it have to be properly input and output matched to minimise the reflection. How do we do this, so in this module, we will be studying about how these impedance matching networks are designed. You may be wondering why impedance matching is so important, it is important because impedance matching is the main determiner of how much power is being, how much power will flow through an active device. It is true that there are other intricacies within the device for example the biasing and how the active device should be acting within a circuit. But most of the circuits, for example if you are designing an amplifier circuit for microwave engineering, it might be a simple say NPN or your PMOS or NMOS type circuits. And once the circuit topology is fixed, all that is left to be designed is the input and output load in the circuit. So, let us consider how to do this design of this input and output matching circuits for active devices, specifically 2 port amplifiers.
So let us consider 1st, we have already studied our Smith chart in the previous lectures. Just to review it once again, we have 2 types of Smith chart, one is the Z Smith chart, then there is a Y Smith chart and then when we combine both, we get what is called as ZY Smith chart. Now suppose we have a load connected let us consider a simple load Z and say it is normalised impedance is this, so this small z is equal to this. And we now connect an inductor in series like this. So, this is an inductor having a normalised impedance zl. So, when we connect this zl, how does the input impedance change.
this point here represents our impedance Z given by 0.5 - J1.0 and we have connected an inductor in series with this impedance as shown. Now we recall now recall that when we connect an inductor in series, then we will be moving in a clockwise direction from on the

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