55.1.3. Indian Institute of Technology, Kharagpur

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.

In this section, we are reintroduced to the topic of Multi-Transistor Amplifiers by Professor Pradip Mandal. The discussion focuses on combining multiple transistor configurations to enhance performance compared to single-transistor amplifiers. This aligns with the course structure that explains different amplifier configurations.

Think of multi-transistor amplifiers like a team of musicians playing together. While one musician can create beautiful music alone, a band playing together can blend different instruments to produce a richer, more complex sound.

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.

Professor Mandal reflects on the earlier discussions about various amplifier configurations using either Bipolar Junction Transistors (BJTs) or Metal-Oxide-Semiconductor (MOS) transistors. Each configuration has its own advantages and disadvantages which need to be understood in the context of multi-transistor amplifiers for better performance.

Imagine trying to create a restaurant menu. While some dishes (single transistor configurations) can be delicious on their own, combining them into a multi-course meal (multi-transistor amplifier) provides a wider range of flavors and experiences for diners.

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.

In this chunk, the focus is on the strategy of combining various configurations to achieve superior performance. By understanding the strengths and weaknesses of each configuration, the goal is to merge them in such a way that benefits outweigh their individual limitations.

It's similar to building a bridge. While individual materials may not be strong enough to stand alone, when combined properly, they create a sturdy and reliable structure.

We shall see that how meaningful mixing it is useful to change the impedance and change the output impedance and maybe what is the overall circuit performance particularly when you consider for the bandwidth of the circuit and what will be their influence so and so on.

This section explains the significance of impedance in amplifier designs. It indicates how combining various configurations can help in altering both input and output impedances, which directly influences the amplifier's performance and bandwidth. Understanding these parameters is essential for designing effective amplifiers.

Think of impedance like the width of a pipe through which water flows. If the pipe is wide, more water can flow through. Similarly, if an amplifier has the right impedance, it allows signals to flow more efficiently.

If we say that common emitter is the main amplifier followed by the common collector, its purpose is to decrease the output impedance. So, we can say that conceptually we can decrease the output impedance of an existing amplifier by simply cascading one common collector stage.

This part discusses the concept of cascading amplifier stages, specifically using a Common Emitter (CE) followed by a Common Collector (CC) configuration. The main idea is that by adding stages, we can modify the output impedance, benefiting overall performance.

Imagine stacking two cups where the top cup is smaller and allows liquid to flow into a larger cup beneath it. The smaller cup (common emitter) reduces the exit pressure and the larger cup (common collector) collects it more efficiently.

In fact, we do also have a special popular configuration called Darlington pair we shall see. In fact, this is similar to common collector common emitter configuration, but we will also see what are the differences and pros and cons.

The Darlington pair is introduced as another important configuration used in amplifiers. It consists of two transistors that work together to amplify current, producing a high current gain. Its similarities and differences compared to other configurations will be discussed further.

Think of two friends who are pushing a car together. Individually they have some strength but combined, they can push much harder and further.

So far we have discussed basic three configurations namely, CE, then CC and then CB configuration. And, we have gone through different derivations and all.

Professor Mandal summarizes the three basic configurations discussed: Common Emitter (CE), Common Collector (CC), and Common Base (CB). This section reflects on various characteristics and performance parameters of these configurations, which will help students understand their applications in multi-transistor amplifiers.

Just like understanding the characteristics of different vehicles (cars, trucks, and bikes) helps you choose the right one for specific tasks, knowing about various amplifier configurations guides you in selecting the right setup for your needs.

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