55.1. Analog Electronic Circuits

Yeah, dear students welcome back to the online certification course of Analog Electronic Circuit. Myself Pradip Mandal from E and EC Department of IIT, Kharagpur, today’s discussion it is Multi Transistor Amplifiers. So far we have discussed about different amplifier configurations, so where one transistor primarily you know single transistor it was doing the amplification and other activities. So, the transistor it was either BJT or MOS transistor and for different configurations we have seen the merits and demerits of the different configurations.

This chunk introduces the topic of multi-transistor amplifiers. It welcomes students and states the focus will be on combining different amplifier configurations that have been discussed previously, such as BJT and MOS transistors used in single configurations. The goal is to improve performance by mixing these configurations effectively.

Think of single-transistor amplifiers like a single worker completing a task. While they may be effective on their own, combining the efforts of multiple workers (multi-transistor amplifiers) can lead to enhanced productivity and better results.

Based on that merits and demerits we shall try to combine different configurations together, so that we can get overall better performance. So, let us see what is the overall plan in the next slide. But, before going to the overall plan let me see our alignment with our course layout. We are in week-6 and we are in between of the block level and module level...

In this chunk, the objective is to combine different transistor configurations to achieve overall improved performance. The instructor highlights that they will be examining how configurations like common emitter, common collector, and others can work together. This integration will aim to enhance qualities like impedance matching and bandwidth.

Imagine mixing different ingredients in cooking. Just like how combining spices and flavors can elevate a dish, cascading amplifier configurations can yield superior performance by balancing each configuration's strengths and weaknesses.

So, the topic we will be covering today it is enlisted here. We shall start with the motivation of going for mixing different configuration together and then we basically we will summarize whatever the earlier discussion we are having...

This section outlines the session's goals. The motivation behind mixing configurations will be discussed, followed by a summary of the previous discussions. The improvements in output impedance and overall circuit performance, especially regarding bandwidth, will also be highlighted.

Think of a sports team composed of players with different skills: some are great defenders, while others excel at scoring. By strategically combining their strengths, the team can perform better together than each player could individually.

So, if you see the common emitter followed by a common collector, its purpose it is to decrease the output impedance...

This chunk explains how cascading a common collector stage after a common emitter stage decreases the output impedance, which allows for better interconnection with subsequent stages or loads. It discusses the general principle that lower output impedance can enhance circuit performance.

Consider a garden hose: if you reduce the hose's diameter (output impedance), water flows smoothly out of it. Similarly, lowering the output impedance helps the amplifier deliver the signal with less resistance.

So, likewise the if we precede common emitter or common collector stage by another one common collector configuration we can increase the input impedance ok...

We can increase the input impedance by placing a common collector stage before an existing amplifier configuration. This increase allows the circuit to accept a higher input signal with less attenuation, thereby improving overall performance.

Imagine a funnel: the wider the opening, the easier it is for liquid to flow into a container. Increasing input impedance helps in accepting more input signal without loss.

In fact, we do also have a special popular configuration called Darlington pair we shall see...

The Darlington pair is discussed as a specific multi-transistor configuration aimed at improving both current gain and input impedance. It operates on the principle of cascading two transistors to amplify the current significantly, making it beneficial in various applications.

Consider the Darlington pair like an effective relay team: the first runner (transistor) passes the baton to the second runner (another transistor), enhancing their combined speed (current) to the finish line (output).

And, then we do have the most counterpart namely we can decrease the output impedance of say one common source amplifier existing common source amplifier by cascading;...

This section compares BJT and MOSFET configurations, emphasizing how cascading can also decrease the output impedance for common source amplifiers. It highlights that while BJTs offer improvements in both input and output impedance, MOS configurations may focus more on output impedance improvements due to their high input impedance.

Think about two types of vehicles: a fast sports car (BJT) that accelerates quickly and can carry a heavy load, versus an energy-efficient electric car (MOS) that excels in range and efficiency. Each serves different needs effectively.

Now, here what we are trying to highlight is basically we consider say one configuration and for this configuration these are the circuit configuration we already have discussed...

The performance metrics of different configurations are revisited, which include voltage gain, input resistance, output resistance, and others. This summary sets the stage for understanding how each configuration can be designed for specific applications.

Assessing each configuration’s performance can be compared to evaluating cars by their speed, fuel efficiency, and capacity. Depending on your needs, one car (or circuit) may be a better choice than another.

So, if we want to use CC for voltage mode amplification, then the game itself is poor. On the other hand, if you if you want to use this CC configuration for current mode amplifier then even though it is current are high current gain...

This conclusion summarizes the findings from comparing the configurations. While each configuration has its strengths and weaknesses, combining them can create a better overall amplifier suited for specific needs. Suggestions for further configurations, like using the CE stage with the CB stage, are also proposed.

It’s like having a toolbox: each tool has its purpose. By mixing and choosing the right tools (configurations), you can tackle any task (design an efficient amplifier) effectively.

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