28.1. Analog Electronic Circuits

Dear students, welcome back to NPTEL online course on Analog Electronic Circuit. Myself Pradip Mandal from E and EC Department of IIT, Kharagpur. So, this is a continuation of our previous topic Common Emitter Amplifier. And, in the previous class, what we have discussed about the relevant theories and today, we are going to discuss more detail of some numerical problems.

In this section, the instructor introduces the topic of Common Emitter Amplifier, highlighting that this discussion is built upon previous theoretical lectures. The aim is to deepen understanding through numerical problems that demonstrate how the theories apply to practical scenarios.

Think of learning to drive a car: in the classroom, you learn the rules of the road (theory), but the real understanding comes when you get behind the wheel and practice driving (numerical problems).

So, as I said that primarily we will be focusing on common emitter amplifier. And, it is having two basic biasing schemes namely the fixed bias and cell bias, and we have discussed about the disadvantage of each of them and then advantages and all.

The Common Emitter Amplifier can be set up using two main biasing schemes: fixed bias and cell bias. Each method has its own advantages and disadvantages. Understanding these schemes is crucial for analyzing the stability and performance of the amplifier in different conditions.

Imagine a chef using a gas stove to cook. Fixed bias is like running the stove on one consistent setting, while cell bias is like adjusting the flame based on what's in the pot – more responsive to changes, ensuring better cooking outcomes.

So, first one it is we will be talking about the bias point stability where we shall demonstrate that fixed bias CE amplifier it is having a major issue in case if the β of the transistor it is getting changed.

This chunk focuses on the concept of bias point stability, particularly within fixed bias Common Emitter Amplifiers. It explains that if the transistor's beta (β) value changes, which can occur due to temperature variations or manufacturing differences, the circuit may need redesigning to maintain optimal performance.

Think of a tightrope walker: if the conditions affecting the rope's tension change (like temperature or humidity), the walker might lose balance and need to adjust their position to stay safe. The same applies to amplifiers – they need to adapt when the parameters change.

And then after that we shall find the performance parameters of CE amplifier having both the schemes biasing schemes namely fixed bias as well as cell biased and then we shall discuss about what are the design guidelines we will be having.

Here, the focus shifts to how to evaluate the performance parameters such as gain, input resistance, and output resistance for both biasing schemes. By analyzing these parameters, students will understand how to maintain appropriate amplifier performance under varying conditions. Additionally, design guidelines are discussed to aid students in creating effective amplifier circuits.

Just like a coach evaluates a player's performance based on different metrics (scoring, assists, defense), engineers assess amplifier performance based on parameters like gain and resistance to ensure it meets the desired standards.

Whereas, in the third one whenever we will be talking about the third one there will be discussing suppose, we do have some requirement of gain and say supply voltage is given to us and then how do we design the circuit, how do we find the values of different components.

This subsection emphasizes the design process when specific performance requirements are provided. The goal is to determine appropriate values for components to achieve desired gain levels and ensure the circuit operates effectively with the given supply voltage.

It's like having a recipe where you want to bake a cake – you need to select the right amounts of flour, sugar, and eggs to meet your taste preferences. Similarly, in circuit design, you pick component values to meet performance targets.

So, here what we have it is CE amplifier having fixed bias. So, we do have fixed bias, the R is given here and here we are starting with the design which is of course, it is a proper design for β = 100.

In this example, a Common Emitter (CE) amplifier is analyzed under fixed bias conditions. It is mentioned that, for beta equal to 100, certain resistance values are used, and the stability of the operating point will be demonstrated.

Consider a student studying under fixed conditions (like specific lighting and temperature). If these conditions are favorable for their study habits (analogous to fixed bias stability), the student can perform well. But if the conditions change (like their study light fluctuating), their performance may drop.

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