75.6.1. Complimentary Circuits

So, the concepts covered in this talk, in this lecture are the following. So, we are going to start with basic operation and then we will be going to discuss detail of characterization of differential amplifier. Namely, how we find the basic parameter values particularly, differential mode gain and common mode gain and so and so, from a given circuit. And then we will be talking about realization of differential amplifier at transistor level.

In this chunk, we discuss the foundational concepts of differential amplifiers. They include understanding how to characterize their performance. Specifically, we focus on two key parameters: differential mode gain (the amplifier's ability to amplify the difference between two input signals) and common mode gain (the amplifier's ability to amplify signals common to both inputs). This section sets the stage for understanding how these amplifiers work and how they can be constructed using different transistor technologies like BJTs and MOSFETs.

Think of a differential amplifier like a person listening to two conversations happening simultaneously. The person (the amplifier) is focused on the difference in what is being said (differential mode gain) and not influenced by the noise from both sides (common mode gain). The ability to pick out the important information from the chaos is similar to the way differential amplifiers function.

So, to recapitulate whatever we have discussed in our previous lecture we do have say this is a main differential amplifier. Where we have the power supply DC supply and ground and then at the input we do have the differential input port having two terminals 1 and 2 and at this input we are given signal or I should say voltage signal and it is having a DC part meaningful DC part and on top of that we do have two signals.

This chunk explains the basic structure of the differential amplifier. It discusses how the input consists of two terminals, each receiving a voltage signal containing a DC component and an AC signal. It is essential for both terminals to have the correct DC bias to ensure proper functionality of the amplifier. The way that signals are processed at the input will significantly influence the output.

Imagine you have two friends (the two terminals) on either side of you (the amplifier). They are both sharing exciting news (the signals), but they need to be at a certain level of excitement (DC voltage) to be heard clearly. If one of them is too calm (low voltage), you might miss their important news. The amplifier helps ensure you catch that excitement.

So, whenever we are talking about the DC level at the output and the DC level at the input, they may be having some relationship, but that relationship cannot be expressed by the two parameter what we have discussed is A and A. This DC voltage relationship can be obtained by considering non-linear characteristic of the entire circuit.

This chunk highlights the importance of understanding the relationship between input and output DC voltage levels in the context of differential amplifiers. It notes that while fundamental parameters (A_dc and A_d) describe signal amplification, the relationship is more complex due to the non-linear characteristics of the circuit. This complexity emphasizes the need to understand both DC and AC analysis for a complete characterization of the amplifier’s performance.

Consider a dimmer switch in your home controlling a lamp (the amplifier). The brightness (output) depends not just on how much you turn the switch (input) but also on the wiring and bulb (the circuit characteristics). Just as you can't predict the lamp’s brightness from the switch position alone due to these characteristics, the output of an amplifier cannot be determined solely from input parameters.

Now once we are in small signal equivalent circuit, then it is basic parameters are differential mode gain and common mode gain as you can see here and we say that ideally we want this differential mode gain it should be as high as possible and this common mode gain on the other hand it should be as small as possible.

In this chunk, we delve into the characterization of the differential amplifier focusing on the small signal equivalent circuit. It emphasizes the goal of maximizing differential mode gain while minimizing common mode gain. These objectives are vital for the effective functioning of differential amplifiers, which should effectively amplify the desired signal while rejecting unwanted noise.

Think of a singer in a loud crowd. The goal (differential mode gain) is for the singer's voice to be heard above the noise, while the noise should ideally not distract from the performance (common mode gain). A well-designed differential amplifier is like a great microphone that captures the singer's voice clearly while filtering out the crowd.

So, let us see the realization of this circuit. There may be different possible realization of differential amplifier, but here we do have a very basic realization of differential amplifier I should say it is basic, but still it is I should say practical circuit.

This section discusses the construction of the differential amplifier. Various implementations are possible, but it highlights a practical circuit configuration that is commonly used. Understanding the construction of these amplifiers offers insights into their functionality and allows for practical application in electronic systems.

Imagine you're learning to build with LEGO bricks. Although many designs are possible, starting with a basic structure helps you understand how to connect the pieces (components) effectively. Once you grasp the basic design, you can modify and create more complex models.

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