53.1. Analog Electronic Circuits

So, dear students welcome back after the break. And before the break we are discussing about Common Base amplifier and Common Gate Amplifier.

In this introduction, the professor welcomes students back to the lecture. They recap that previous discussions included the Common Base and Common Gate amplifiers. This indicates that the lesson will continue from earlier topics, focusing on their properties and applications.

Imagine you are part of a team project where each member is responsible for different parts. Just like how we continue discussions from the last meeting to enhance our group's understanding, here the professor builds upon previously discussed concepts to deepen the students' knowledge.

So, here we do have the common gate amplifier. And next to this common gate amplifier what we are looking for it is; we are you might have observed that at the gate we are connecting one capacitor C . In fact, if you see the previous circuit. So, they are also you can see that in common base amplifier in common base amplifier here also we do have the C that makes the base node AC ground and with that assumption we have done the analysis. Now it is very important to keep this capacitor sufficiently large so, that the base node particularly for the signal it should be working as a ground.

This chunk discusses the importance of a capacitor (C) in the Common Gate and Common Base amplifiers. The capacitor is essential because it helps set the base node to AC ground, which is crucial for the operation of the amplifier. A sufficiently large capacitor ensures that the signal behaves correctly, allowing for accurate analysis and functionality of the amplifier.

Think of the capacitor as a large sponge soaking up water in a bathtub. If the sponge is too small (like a too-small capacitor), it won't be able to hold enough water (or signal), causing issues with the overall system. However, if the sponge (capacitor) is large enough, it can effectively manage the water (signal), keeping everything running smoothly.

So, we are going to talk about performance of the common base amplifier without this C without the C . So, in our next example numerical example that is what we are going to do and we will see that what are the performance degradations are happening due to eliminating this capacitor.

Here, the focus shifts to analyzing the performance of the Common Base amplifier when the capacitor is absent. This investigation aims to highlight how critical the capacitor is since removing it leads to degradation in performance parameters such as input resistance and voltage gain.

Consider a car engine. If a crucial component (akin to a capacitor) is removed, the engine won't run smoothly, and its performance will degrade significantly. This analogy emphasizes how essential certain parts are for the overall function of a system.

Now let me draw the small signal equivalent circuit, small signal equivalent circuit of the main amplifier, try to explain that what kind of effects are there.

In this part, the professor introduces the small signal equivalent circuit of the amplifier. This circuit is essential for understanding how the amplifier reacts to small changes in voltage or current. By analyzing this circuit, students can identify the effects of various components on performance.

Consider a sound system where you adjust the volume to hear better. The small signal equivalent circuit is like the controls on the system that help you fine-tune the sound. Understanding how each control affects the overall output helps ensure the best listening experience.

So, if we recall see ok. So, let me let me try to erase this board and try to plug in this expression in the expression of to get the affected voltage gain.

The discussion emphasizes recalculating the voltage gain and input resistance considering the absence of the capacitor. The shift in these parameters due to component changes is crucial for understanding overall amplifier performance.

Imagine a team project where one team member’s absence (similar to removing the capacitor) drastically changes the group's dynamics and productivity. Similarly, the voltage gain changes when the capacitor is not present, influencing the amplifier's effectiveness.

So, if you see the potential division we do have here it is r = 5.2 k and these two resistances is together it is 50 k. So, now, it is very obvious that whatever the stimulus we are putting voltage wise only one tenth it is coming here.

This section illustrates how the input resistance is significantly affected by the configuration of resistances when the capacitor is removed. It draws attention to how only a small fraction of the input voltage reaches the desired component due to the voltage division principle.

Think of trying to fill a cup with water using a small hose. If the hose is narrow (representing increased input resistance), only a small amount of water (voltage) can come through at once, leading to inefficient filling. This analogy emphasizes how resistance affects performance.

So, the summary is that this input resistance it is getting modified here and also we do have this R.

In concluding the analysis, the professor summarizes the changes in input resistance and voltage gain resulting from the absent capacitor. This highlights the adjustments that must be made to understand how these parameters affect amplifier design and functionality.

Think of modifying a recipe when you realize you are missing an ingredient. Just as you adjust other elements to compensate, in circuit design, understanding how one component affects everything else is crucial.

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