48.1.4. Summary of Design Guidelines

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, then we can find what will be the value of this one and also the corresponding DC voltage here.

In circuit design, especially for a common drain configuration, the starting point is determining the output resistance. Once the output resistance is established, we move on to calculating the transconductance (g). Afterward, we use these values to calculate the required drain current (ID). Finally, this information allows us to determine the necessary DC voltage, which could potentially come from a previous stage of the circuit. Following this sequence ensures systematic design based on defined electrical parameters.

Think of designing a house. You first set a foundation (output resistance), then decide on how many floors the house should have (transconductance), which informs how much power you need for each room (drain current). Finally, you ensure the electrical supply (DC voltage) meets these needs, just like linking every part of a house construction together based on previous decisions.

In fact, this DC voltage it may be coming from the previous stage. So, in case if this is given to us; accordingly, then we can calculate the corresponding R.

The DC voltage that we use in the design might not be newly generated; it could originate from earlier stages of the circuit. If we already know what this voltage is, we can proceed to calculate the corresponding load resistance (RL) that will ensure the circuit functions as desired. This step is critical as it ties the design of each stage together, making success in one stage dependent on the accurate specifications from the previous one.

Imagine you're making a multi-part recipe. You need to know how sweet your previous desserts were (DC voltage) to decide how much sugar to add in your next dish (R). If the last cake was very sweet, you might hold back on the sugar to ensure the flavors balance perfectly.

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 guidelines presented for the common drain circuit can also be applied to the common collector configuration. In this case, the design begins with specified requirements like the upper cutoff frequency and load capacitance. From these parameters, we deduce the necessary resistance and current, maintaining consistency in our methodological approach to circuit design.

Consider a flower garden where you want to plant a variety of flowers (the common collector). Different flowers need specific approaches based on their requirements (upper cutoff frequency and load capacitance). For instance, sunflowers thrive better with certain soil conditions, just like certain circuits have best-performing parameters. By knowing these preferences, you ensure your gardening (circuit design) is successful.

Whatever the calculation we will be doing, we are assuming that the remaining parameters are given to us. Namely, the device parameters particularly the early voltage and C.

In all these calculations, it's important to note that we assume specific device parameters—the early voltage and capacitances among others—are provided and will stay constant during the design process. This assumption allows us to focus solely on the variables we control, helping to ensure accuracy and effectiveness in our design approach.

Think of preparing a dish where the recipe assumes you already have certain spices and ingredients (like early voltage and capacitances). This makes it easier to focus on how to cook and adapt those ingredients without worrying about sourcing them again, similar to maintaining a steady foundation in circuit design.

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