48.2.1. Review of Design Process

So, the summary of the design guidelines is that we start from output resistance particularly for common drain circuit then we calculate g, we calculate the required I to achieve the required I.

In the design process for a common drain circuit, we begin by determining the output impedance. This is fundamentally important because it influences how effectively the circuit can function. Once we have this output resistance figured out, we move to compute the transconductance (g). This parameter reflects how the output current will change in relation to changes in the input voltage. Lastly, we will find the necessary drain-source current (I_D) needed to meet the output requirements. This stepwise approach ensures that each aspect of the circuit's performance is carefully addressed.

Think of it like planning a road trip. First, you need to recognize the maximum load your car can handle (output impedance). Next, based on your car’s fuel efficiency (transconductance), you calculate how much fuel you’ll need (drain-source current) for the entire journey. Understanding each part ensures you reach your destination smoothly.

So, from R we calculate g and then from that we calculate I or I_D. And to achieve this I_D, we can find what supposed to be the meaningful DC voltage and what will be the corresponding meaningful resistance of the source.

Once we have established the output impedance (R), we proceed to compute the transconductance (g) using the relationships defined in the circuit analysis. From this point, we can determine the necessary drain-source current (I_D). After that, it’s crucial to find the appropriate DC voltage that can support the required I_D, as well as calculate the source resistance. This part of the process is vital, as it directly affects how the circuit interacts with its power supply and influences its overall performance.

Imagine you're setting up a new watering system for your garden. First, you need to ensure you have the right amount of water pressure (R), then decide how quickly you should be running the system (g). Based on this, you’ll determine how much water you want each plant to get (I_D), and finally, you'll check how strong your pump needs to be (DC voltage). Each step supports the next, ensuring all parts work together harmoniously.

So, better, we should avoid this resistance and ideally we want this resistance should be 0. So that unnecessarily we do not want to complicate the circuit and contribution of the C_gd.

In circuit design, it is essential to minimize any resistances that might complicate the circuit unnecessarily. Ideally, a certain resistance should be avoided entirely (should be zero) to simplify the design. This consideration helps ensure that the circuit performs optimally by avoiding added complexities that could degrade the signal quality or affect frequency response, such as unwanted capacitance effects.

Think of it like planning a party: you want to keep it simple and enjoyable without too many distractions or complications. If you start adding too many elements, like complicated games or multiple food stations, it could overwhelm your guests and take away from the fun.

So, similar kind of guidelines it can be followed for the common collector circuit also. Where, again the information may be given or rather requirement it will be given for the upper cutoff frequency for a given load capacitance.

The design principles we discussed for the common drain circuit also apply to common collector circuits, although there are some variations. In designing a common collector circuit, guidelines including the target upper cutoff frequency and the load capacitance are important. From this information, you can calculate the necessary values for resistances and other parameters to ensure the circuit will operate as intended.

It’s like cooking: if you’re making both pasta and sauce simultaneously (common collector and common drain), you would follow similar steps for each dish, but adjust the ingredients and cooking times based on the specific recipe requirements to ensure a delicious outcome.

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