77.2.1. Introduction

So, dear students welcome back to our NPTEL online certification course on Analog Electronic Circuit myself Pradip Mandal from E and EC department of IIT Kharagpur. Today’s topic of discussion it is: Differential Amplifier and in fact, today we are continuing differential amplifier, but today we will be primarily focusing on Circuit Analysis and maybe towards the Numerical examples.

The introduction starts by welcoming students back to the course. The speaker, Pradip Mandal, emphasizes that today's lesson will focus on the differential amplifier, specifically its circuit analysis and possible numerical examples. Understanding differential amplifiers is crucial in electronics as they are foundational for many applications.

Think of an orchestra where different instruments (representing signals) play together to create a harmonious sound (output). A differential amplifier is like the conductor, balancing these signals to produce a clear output, allowing us to focus on the music rather than the noise.

So, the overall plan we are in module-7 and; under the module-7 we do have the plan of going for Differential Amplifier. So, in our previous lecture we have talked about basic structure and working principle of differential amplifier, prior to that we have discussed about single ended signaling versus differential signaling, they are part of the differential amplifier background. And today we are going to discuss more on analysis of differential amplifier.

The speaker outlines the structure of the module. They will be building on previous lessons about the basic structure and working of differential amplifiers, as well as contrasting single-ended and differential signaling. The focus will shift to analyzing differential amplifiers in more depth, which will enhance students' understanding of their functionality.

Imagine learning to bake a cake. In previous lessons, you learned about the ingredients and tools required (structure). Now, we delve into the technicalities of the baking process (analysis), transforming our theoretical knowledge into practical skills.

Specifically, for two modes of operation differential mode and common mode operation and their corresponding gain. And, then we will also talk about large signal analysis from where we can get the signal swing possible output signal swing and the range of DC voltage which is referred as Input Common Mode Range.

This chunk highlights the two primary modes of operation for differential amplifiers: differential mode and common mode, along with their respective gains. Moreover, it introduces large signal analysis, which helps determine the maximum signal swing and the acceptable range of input common mode voltage. Understanding these concepts is fundamental for designing circuits that work effectively with differential amplifiers.

Consider a radio station transmitting music. The music signal can be thought of as the differential mode, while background noise is akin to common mode. Knowing how to filter out noise allows us to listen clearly to our favorite songs. Similarly, analyzing signal swings helps ensure amplifiers perform well under varying conditions.

So, we shall start with small signal equivalent circuit of differential amplifier both; implemented by BJT as well as MOSFET. And, then we shall talk about small signal analysis. Specifically, for Differential mode of stimulus or Differential mode of operation then, Common mode stimulus or Common mode operation and then combined one which is referred as generalized stimulus and then we may have a special case which is referred as pseudo differential stimulus.

The speaker mentions that the session will begin with examining the small signal equivalent circuit of differential amplifiers, focusing on both BJTs and MOSFETs. The analysis will cover different operational modes including differential and common modes, along with generalized and pseudo differential stimuli. This method helps in simplifying complex circuits for better understanding and analysis.

When tuning a guitar, you adjust each string to achieve the right pitch (the correct operational mode). Similarly, analyzing small signal equivalent circuits allows engineers to 'tune' amplifiers for optimal performance in various electronic applications.

And then we will be going for Large signal analysis to start with, we shall discuss about DC operating point analysis and then we shall talk about; the input DC voltage range over which devices are in proper region of operation which is commonly known as Input common mode range and then, we shall talk about the possible signal swing for a given circuit which referred as output signal swing. Numerical examples it will be followed after that, but I am not sure whether we will be able to cover today, but yes, this is the overall flow.

In this part, the speaker outlines the approach for analyzing the differential amplifier, starting with large signal analysis. They will discuss the DC operating point and the input common mode range where amplifiers function optimally. The output signal swing, indicating the voltage range for maximum signal output, will also be explored. The section concludes with a mention of numerical examples to solidify understanding.

Think of figuring out the optimal temperature range for baking. Just like you need to keep the oven at the right temperature to ensure the cake rises correctly, engineers must operate amplifiers within their optimal voltage ranges to achieve the best performance.

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