34.1.1. Numerical Examples and Design Guidelines

So, our plan today it is yeah; so, the concepts we are going to cover here today is this guidelines of common source amplifier design. And, we will be going through numerical exercise through that exercise we will know that how to select the value of the resistors may be capacitors also some extent.

In this section, we will focus on the design guidelines for a common source amplifier, which is a crucial circuit in analog electronics. The purpose is to understand how to choose the correct values for different resistors and possibly capacitors used in the amplifier's circuitry. This process is essential as it ensures the amplifier operates effectively in practice. Through numerical examples, we'll illustrate the selection process for these components, highlighting their impact on the performance of the amplifier.

Think of designing a common source amplifier like cooking a dish. Just as you need to select the right ingredients in the right proportions to achieve the perfect flavor, choosing the correct electronic components ensures that the amplifier functions correctly and meets our desired specifications.

Now, so far what we have covered is the analysis; so, what we have done it is suppose you do have this common source amplifier and then in case the device components or other K×W device parameters are given to us namely . And, then threshold voltage of the transistor L if it is given and also the supply voltage is given to us.

Before diving into design, we've already gone through the theoretical analysis of the common source amplifier. This analysis involves understanding the circuit when key parameters like device components (K×W ratio), threshold voltage, and supply voltage are provided. Knowing these parameters allows us to calculate important aspects of the amplifier such as gain and input resistance, which serve as a foundation for the design phase.

Consider evaluating the specifications of a vehicle before purchasing it, such as engine capacity, fuel efficiency, and safety ratings. Just like these specifications guide your decision, the parameters of the amplifier inform the design choices we will make.

Today we are going to discuss the reverse process, namely in case the circuit is given to us and the circuit topology is given to us along with device parameters and the supply voltage is given to us. And, we need to find; we need to find the values of these resistors namely the bias resistors R , R , then R .

In this part, we shift from analysis to design. Given a predefined circuit topology along with the device parameters and supply voltage, our task is to determine the appropriate values for the bias resistors (R1, R2, RD). This selection is crucial as it affects the amplifier's performance, ensuring that it can provide proper signal swings while maintaining the transistor in its saturation region.

Imagine building a custom piece of furniture where you have specific dimensions and materials in mind. You must select the right sizes and types of wood to ensure the piece is functional and aesthetically pleasing. Similarly, choosing resistor values is about customization to achieve the desired performance in your amplifier.

So, we want this swing should be as high as possible and this is the limit. So, if the DC operating point it is skewed towards the V of course, positive swing positive side swing it will be less.

The DC operating point is a critical parameter in amplifier design. It refers to the bias point around which the amplifier operates. For optimal performance, particularly in terms of output signal swing, this point should be set ideally at a midpoint between the maximum and minimum voltage levels allowed by the circuit. This ensures that both positive and negative swings of the output signal are maximized, preventing distortion.

Think of a swing at a playground; if it's positioned too high on one side, it restricts how far it can swing back down. Setting the operating point in a balanced manner is like ensuring the swing can go back and forth freely.

So, let me start that process yeah. So, what we have here it is just to start with as an example let you consider that I = 0.5 mA.

Let's illustrate our design approach with a numerical example where we target a drain current (ID) of 0.5 mA. Using the characteristic equations of the common source amplifier, we can derive relationships that will guide us in choosing appropriate resistor values. For instance, knowing the desired current allows us to calculate required gate-source voltage and subsequently the resistor values needed to achieve this configuration.

This is akin to budgeting your finances for a trip. If you know how much money you want to spend (the current), you can plan how much you can allocate for accommodation, food, and activities (which would parallel the resistor values we calculate).

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