55.1.2. Department of Electronics and Electrical Communication Engineering

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.

In this introduction, Professor Pradip Mandal welcomes students to discuss Multi-Transistor Amplifiers. He highlights that previous lectures covered various amplifier configurations utilizing a single transistor, such as BJTs or MOS transistors. The aim is to build upon these discussions to explore combining configurations for enhanced performance.

Think of a single transistor like a solo musician playing a song. While they can play beautifully alone, combining their talents with other musicians (more transistors) can create a richer, fuller sound (better amplifier performance).

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.

The professor mentions that the focus will be on combining various transistor configurations to enhance performance. This involves looking at the course layout and understanding how these configurations, when cascaded, can improve parameters such as output and input impedance.

Imagine each configuration as a piece of a puzzle. By combining them strategically, you can create a beautiful picture (enhanced amplifier performance) instead of leaving some pieces aside.

So, philosophically we can say there these are building blocks or they may be modules and to be precise whatever the topic we will be discussing here it is common emitter, common collector cascaded together. Then may be common source and common drain configurations cascaded together.

The professor explains that the configurations to be discussed can be viewed as building blocks or modules that can be cascaded together. Specific configurations mentioned include common emitter and common collector amplifiers, which work well together to enhance the amplifier's performance.

Consider building a LEGO tower; each piece (amplifier configuration) must fit well with the others to create a sturdy and tall structure (a high-performance amplifier).

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.

The lecture will first discuss the motivation behind mixing different amplifier configurations. These motivations include gaining improved performance metrics such as output impedance and bandwidth. The session aims to summarize previous discussions to situate the current topic within a broader understanding.

It’s like combining different flavors in cooking; you mix ingredients not just for taste but for a better overall dish (amplifier performance).

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 either we may have simple CE amplifier or we can have CE amplifier with emitter degenerator bypassed with C...

In this discussion, the focus is on evaluating the performance metrics of different amplifier configurations, such as voltage gain, input resistance, output resistance, and current gain. These metrics will help assess which configuration may be best suited for specific applications.

Think of performance metrics as the specifications for a car (e.g., speed, fuel efficiency); knowing these helps you choose the right car for your needs (the right amplifier for your circuit).

So, let us look into the R and its expression it is given here and R it is major contribution coming from the active devices given here and R it is; R it is basically the bias circuit. So, if I consider the output resistance coming from the main configure on the amplifier we can say it is very high that is because this r ,R and R in parallel it is getting amplified by intrinsic gain of the amplifier namely g r which is intrinsic gain of the transistor.

In exploring the different circuits, the output resistance is discussed, noting that it can be high due to the configuration. The intrinsic gain of the transistor amplifies the contributions from various resistances present in the configuration, affecting performance in intended applications.

It's like how a good amplifier can take weak sounds (current) from a microphone and make them strong enough to fill a room. The quality of your sound system will depend on the resistances and configurations used.

So, if you put all these three configurations together namely CE, CC and CB and if you enlist the qualitative parameter you know values or I should say if you consider then together probably we can make a meaningful decision to see what kind of mixing of different configurations it will be useful.

The conclusion emphasizes the evaluation of CE, CC, and CB configurations to determine effective ways to mix them for enhanced performance in either voltage or current amplification applications. This synthesis of configurations aims for broader utility in circuit design.

Consider this like composing a piece of music; you choose the best notes from each instrument (amplifier configuration) to create a harmonious symphony (optimal performance).

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