30.1. Common Emitter Amplifier (Contd.)

Hello, so now so, welcome back to this NPTEL online course on Analog Electronic Circuits. This is of course, it is we are having this course for maybe last 2 to 3 weeks, it is continuation of that topic of Common Emitter Amplifier. We have discussed about the theoretical aspect and some of the numerical examples, and in the previous class we could not complete the numerical problems all. So, today we are discussing some more numerical problems.

The instructor begins by welcoming students back to the course, emphasizing that this lesson continues from previous discussions on the Common Emitter Amplifier (CEA). In prior classes, theoretical aspects and numerical problems were covered, although not all problems were completed previously. This session is intended to expand on previous examples and focus on designing the CEA based on provided requirements.

Imagine you are working on a complex recipe where some steps from previous cooking sessions were left unfinished. Each time you come back, you review and expand on your understanding, much like building upon the previous lessons in your electronics course.

So, today what will be doing is that in case if we have to design one common emitter amplifier for a given requirement, then how do you proceed and what may be the design guidelines we need to follow.

In this part of the discussion, the instructor outlines the essential steps needed to design a common emitter amplifier based on specific requirements. This includes understanding the key parameters needed, such as supply voltage and transistor type, which will influence the design decisions.

Designing an amplifier is like building a custom piece of furniture. You start with understanding the space (requirements) you have to work with, materials (components required), and the desired style (design guidelines) before you start building.

And, so, we are going to discuss detail about the design guidelines of common emitter amplifier. And, in case if the topology is fixed and if it is decided to be fixed by us topology. And, then how do you proceed first thing is that we are assuming that these informations are available particularly the supply voltage it is given to us.

Here, the instructor highlights that the design guidelines will be based on several critical parameters. An important factor is the topology of the amplifier, which must be predetermined. The supply voltage is one of the primary specifications provided, helping to dictate the subsequent design decisions.

Consider cooking with a recipe that specifies the oven temperature (supply voltage). Just as the cooking process will change based on whether the oven is set to 350°F or 450°F, the amplifier's behavior will depend on the supply voltage you choose.

We can say that in the power dissipation it is essentially means that, the value of the collector current. And, then the additional information it may be required is that what may be the input resistance of the circuit, small signal or large signal input resistance, then output resistance of the amplifier.

In this section, the importance of understanding power dissipation is emphasized. Power dissipation primarily relates to the current flowing through the transistor. Additional parameters to consider include the input and output resistance of the circuit, which affect performance characteristics such as gain and overall efficiency.

Imagine your home’s electrical system. Just like knowing how much current (power) your appliances draw can prevent overload on your circuit (power dissipation), understanding the currents in the amplifier design prevents overheating and ensures efficient operation.

So, as I said that this is what we are from in fact, we already have covered significant part of the numerical examples. And, particularly the operating point and then the and it is stability and then finding performance matrices.

This part discusses how the voltage gain of the common emitter amplifier and the output swing are related to the design. Understanding how to maintain stability and a favorable operating point ensures the amplifier can achieve the desired performance without distortion.

Think of a see-saw in a playground. If you want it to tilt in a balanced way (operating point), you need to position the riders correctly (gain vs. swing). If everyone is too heavy on one side, it won’t function as intended.

So, I should say this is the upper limit of the voltage gain giving importance to the output swing. And, in this case if I say that V is very small and then we can say that upper limit of the voltage gains, we can practically you can say this is .

Here the instructor explains how to determine the upper limit of voltage gain by considering various constraints such as supply voltage and output swing. By making appropriate calculations, one can optimize the design for better performance outcomes.

This is similar to tuning a musical instrument. The maximum volume (gain) you can get from the instrument depends on how tightly you tune each string (parameters). If one is too loose, it affects the entire sound output.

So, once we decide that the output swing we want it should be 5 V this is a 2 V, then naturally the drop across this resistance it is also getting fixed, because this is the we like to say this operating point almost at the middle.

In this final chunk, the instructor provides guidance on how to finalize component values to ensure that the amplifier meets the predefined output swing requirements. Decisions regarding resistor values directly influence the voltage drop and the overall gain.

This can be likened to planning a road trip. You must consider how much fuel (voltage swing) you need to reach each destination. Adjusting one stop (resistor value) affects the entire journey (circuit performance).

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