53.2. Examples and Analysis

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 instructor welcomes students back from a break and recalls the previous discussion about Common Base and Common Gate amplifiers. This sets the stage for continuing with practical numerical examples relevant to these amplifiers.

Imagine returning to a class after a lunch break. Just as you would review what was previously discussed before diving back into a new exercise, the instructor does the same to help students remember and prepare for practical applications of their learning.

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_G.

The instructor points out the common gate amplifier circuit and highlights the use of a capacitor at the gate. This capacitor is vital for certain analyses, as it allows the gate node to function as an AC ground, crucial for the correct operation of the amplifier in AC applications.

Think of the capacitor at the gate like a sponge soaking up water. Just as a sponge can absorb excess liquid and help maintain an even level in a container, the capacitor helps stabilize the voltage at the gate, making it easier to manage AC signals.

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.

The instructor emphasizes the need for a sufficiently large capacitor to maintain appropriate ground conditions for the AC signals at the base node. Removing the capacitor could lead to performance degradation in terms of input resistance and voltage gain, which will be explored in subsequent examples.

Imagine trying to balance on a seesaw. The larger the base (or the capacitive effect), the easier it is to maintain balance. Similarly, a large capacitor ensures that the amplifier can effectively stabilize the signal it's processing.

we will see that what are the performance degradations are happening due to eliminating this capacitor.

The instructor will now analyze the degradation in performance metrics, including voltage gain and input resistance, that occurs if the capacitor is not used. The pedagogical goal is to help students understand the importance of the capacitor in circuit performance.

Think of the capacitor's role as similar to that of oil in a car engine. Just as oil ensures that all parts of the engine move smoothly and efficiently, facilitating better performance, the capacitor helps ensure that the amplifier functions at its best. Without it, performance declines significantly.

if we have the C_B connected. So, if I say the expression of the voltage gain with C_B it has been enlisted here.

This section examines the voltage gain and input resistance expressions when the capacitor is present, allowing students to see how specific circuit parameters are mathematically represented. Understanding these relationships is essential as it forms the basis for analyzing circuit performance.

Consider the differences in sound between a guitar with and without an amplifier. When the amplifier (or in this case, the capacitor) is connected, the sound (or output voltage) is significantly louder and clearer. The equations are analogous to understanding how much louder the sound becomes with the right components in place.

The input resistance it is getting modified here... now so, likewise the voltage gain.

Here, the discussion focuses on how removing the capacitor alters the input resistance and voltage gain of the amplifier circuit. These changes can often have significant consequences in how effective the amplifier is for the intended application.

This is akin to tuning a musical instrument. Removing essential components (like the capacitor) can drastically alter the tone and quality of the sound emitted, just as it changes the electric signals in the amplifier.

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

The instructor summarizes that both input resistance and voltage gain are adversely affected by the lack of the capacitor. This highlights the capacitor's critical role in maintaining circuit integrity and optimal performance in amplifiers.

Think of the importance of reminders in your daily life. Just like reminders keep you on track for tasks and responsibilities, capacitors maintain the necessary conditions for circuits to operate properly, ensuring they deliver optimal performance.

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