59.1.1. Prof. Pradip Mandal

Welcome back after the short break. So, we are talking about the CE-CC and now we will be moving to MOS counterpart.

This introduction sets the stage for discussing common source amplifiers, which are a fundamental type of amplifier in analog electronics. The mention of the CE-CC (Common Emitter to Common Collector) indicates a transition to discussing their counterparts in MOS technology, suggesting that the concepts will be similar but adapted for a different type of transistor.

Think of it like switching from one style of cooking to another, such as moving from stovetop cooking to baking. While the basic techniques (like heating and combining ingredients) are similar, the tools and outcomes can change quite a bit.

So, in the next slide we will be talking about see common source amplifier again this numerical exercise we have seen before. So, this is prime and the main common source amplifier and sorry and then we have the information given here about the device namely which is 1 mA/V², threshold voltage it is 1 V, supply voltage it is 12 V and so and so.

In this chunk, we are introduced to specific parameters that define the functioning of the common source amplifier. Key specifications include the transconductance (1 mA/V²), which indicates how effectively the amplifier converts input voltage into output current, a threshold voltage of 1 V (below which the amplifier does not operate), and a supply voltage of 12 V, which powers the circuit.

Imagine a faucet: the supply voltage is like the water pressure, the threshold voltage is like the point where water starts to flow, and transconductance represents how much water flows out for a given turn of the faucet. Just as these variables dictate how much water you get, they dictate how the amplifier behaves.

And, we have seen that using this information we obtain V = 3 V and then I GS DS obtain it was 2 mA and then corresponding small signal parameter g it was 2 mA/V. So, the corresponding voltage gain; voltage gain it was g into output resistance.

From the given specifications, we calculate the output voltage (V) and the drain current (I_D) of 2 mA. The small signal transconductance (g_m) is calculated to be 2 mA/V, which allows us to compute the voltage gain of the amplifier. The importance of this gain is crucial as it reflects how much the input signal is amplified.

Picture a microphone that amplifies sound. If a soft whisper (input signal) comes in, and it outputs a loud voice (output signal) at a specific ratio, that ratio can be considered the voltage gain of the system. The higher the gain, the louder the sound compared to the initial whisper.

So, the voltage gain it was g R and so that becomes 2 m × R is 3 k; so the corresponding voltage gain it was only 6.

In this chunk, we multiply the transconductance (g_m) by the output resistance (R_D, set at 3kΩ) to arrive at the gain figure of 6. This linear relationship shows how changes in either g_m or R_D directly impact the gain, which is fundamental for designing amplifiers.

Imagine a bicycle rider. If the rider is strong (representing transconductance) and the bicycle is in good condition (analogous to output resistance), the bike goes fast (high gain). If the rider gets tired or the bike gets rusty, the speed decreases (lower gain).

The upper cut off frequency for this case f it was into load capacitance of 100 pF. So, it was and then 3 k into this one 100 p; that means, 10⁻¹⁰ yeah. And in fact, if you calculate it this gives us 530 kHz.

This section involves calculating the upper cutoff frequency of the amplifier using the formula that relates it to the load capacitance and the output resistance. The upper cutoff frequency is the point beyond which the amplifier cannot efficiently amplify signals, providing insight into the bandwidth of the amplifier.

Think of a speaker. It can only produce clear sound within a certain frequency range, just as the amplifier can only effectively amplify signals up to this cutoff frequency. Frequencies above this point get distorted just like sounds that are too high or low get ignored by the speaker.

So, the common source amplifier it is primarily it is having a gain of 6 and then upper cut off frequencies 530 kHz, we are not going to calculate the lower cut off frequency primarily because our intention here is to see the enhancement of the bandwidth by the use of common drain stage.

After analyzing the common source amplifier parameters, the text indicates the necessity of using a common drain (CD) stage to extend the bandwidth of the overall amplifier system. This section underscores the strategy of cascading stages to achieve desired performance characteristics.

Imagine building a multi-story library. The first floor gives access to general books (common source stage), but the second floor adds more specialized resources (common drain stage), effectively expanding the research capability of the library, just as cascading amplifiers expands the bandwidth.

So, we do have in the next slide we do have that example here. So, all the information’s are we are keeping it same we do have additional common drain stage coming out of the transistor M2 and the its bias circuit R and R it is given here it is 1.5 kΩ.

The following segment presents a practical numerical example incorporating a common drain stage in the amplifier circuit. It discusses the biasing of additional components and how this affects the overall functionality and performance of the amplifier. This demonstrates applying theoretical principles in real-world situations.

Consider this addition like bringing in an expert to help manage a project. This new person (the common drain stage) may not be responsible for the project's core tasks, but they enhance the workflow and efficiency, creating a better overall outcome.

So, how do you find the corresponding current here I? So, there is a method first of all this I flowing through this R creating a drop which is defining the source voltage...

This part elaborates on a method for determining the output current (I_DS) in the common drain amplifier by analyzing the circuit loop. It emphasizes how voltage drops across resistors help define the operating conditions of the transistors involved, presenting a systematic approach to calculating these values.

Think of it like managing water flow in a series of pipes (the resistors). The pressure drop (voltage drop) across each pipe affects how much water (current) can flow through the entire system, allowing for control over the final output.

So, we can say that V_GS; V ‒ V = 6 V ‒ this V ‒V is 1 V ok. And so what is this one we do have 5 here... we can see that we can find the corresponding current.

In this segment, voltage equations are set up to continue the process of finding the output current from the biasing point. By expressing these relationships mathematically, the text illustrates how to derive current expressions associated with gate-source voltages.

It's like figuring out how many steps you can take once you know the distance between your starting point and final destination (voltage levels). By calculating each step (voltage drop), you can figure out how far you're allowed to go (current flow).

I think let me then summarize most of the things whatever we have planned we have covered here...

At the conclusion of the lecture, a summary is provided that encapsulates the various aspects of combining common emitter and common collector configurations. It reflects on the benefits of cascading these amplifiers to enhance bandwidth and input resistance, drawing attention to practical implications and reinforcing the core concepts discussed.

If we liken the entire course to building a complex bridge, the summary acts as the final inspection before opening it to traffic. Each part of the journey (the sections) reinforces how all the pieces come together to create a functional whole.

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