77.2. Differential Amplifier: Analysis and Numerical Examples

So, dear students welcome back to our NPTEL online certification course on Analog Electronic Circuit. 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.

In this introduction, we are welcomed back to a course on Analog Electronic Circuits, specifically focusing on Differential Amplifiers. This section outlines that the primary goal is to analyze differential amplifiers in detail, building on previous knowledge. It emphasizes the importance of understanding the circuit's behavior.

Think of a differential amplifier as a translator between two languages; it helps to convey information clearly by differentiating between signals, just as a good translator picks up the nuances of two languages.

In our previous lecture we have talked about basic structure and working principle of differential amplifier... the concepts we are going to cover are the following.

Here, the speaker reviews the earlier discussions about the structure and fundamental principles of differential amplifiers. The two modes of operation, differential mode and common mode, are highlighted, where each operation yields different gains, focusing on real signals.

Consider a concert with two musicians playing in harmony (differential mode) versus both playing the same note with different instruments (common mode). Each approach creates a distinct auditory experience, just as the two modes create different amplifier functionalities.

We shall start with small signal equivalent circuit of differential amplifier both; implemented by BJT as well as MOSFET.

The text introduces the idea of a small signal equivalent circuit for differential amplifiers designed with Bipolar Junction Transistors (BJTs) and Metal Oxide Semiconductor Field-Effect Transistors (MOSFETs). This small signal model simplifies the analysis by linearizing the components for small voltages.

Imagine tuning a guitar to play a soft melody. The small adjustments you make for subtle changes are like the small signal equivalent circuit — focusing on minor variations to achieve harmonious sound.

Specifically, for two modes of operation differential mode and common mode operation and their corresponding gain.

This chunk discusses the analysis of the two operational modes of the differential amplifier: differential mode, where different voltages are applied to each input, and common mode, where the same voltage is applied. Each mode has a distinct gain and behavior, making them crucial for signal analysis.

Think about listening to two different radio stations at once (differential mode) versus listening to the same station on two radios (common mode). Each scenario offers unique audio qualities and understanding.

Then we shall 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.

In this section, the focus shifts to large signal analysis, which investigates the maximum signal swing and the permissible range of DC voltages—known as the Input Common Mode Range—where the amplifier operates effectively without distortion or cutoff.

Photo sensors have a maximum light exposure they can handle before the image becomes overexposed. Similarly, differential amplifiers have a signal swing range they can manage without losing fidelity.

Now, in our previous lecture we have discussed for better understanding of the circuit operation... we are going to analyze the circuit in this form.

The speaker explains the necessity of realizing the small signal equivalent circuit for better comprehension and analysis of the differential amplifier. By splitting certain components, they simplify the circuit for effective study and practical application.

Consider chefs chopping ingredients for a recipe. By breaking down large items into smaller pieces, they can prepare the dish more easily and effectively, just as circuit reduction aids in analyzing complex systems.

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.

The section wraps up with a note that practical numerical examples will follow to further cement the concepts discussed. This transition signifies that theoretical understanding will soon be applied in practical scenarios, crucial for deepening knowledge of differential amplifiers.

Like students preparing for a math exam, learning theory is important, but solving practice problems is where real understanding takes off. Numerical examples serve this very purpose in learning about amplifiers.

--