54.2.2. Circuit Analysis

So, welcome back after the short break. So, we were here we do have the Common Gate Amplifier and let us assume that the performance requirements are given namely voltage gain it is given output swing it is given and input impedance is given to us and then, we need to find the values of different parameters.

In this section, we start discussing the Common Gate Amplifier, assuming certain performance specifications have been provided. These include voltage gain, output swing, and input impedance. The goal is to determine the appropriate values for various components based on these specifications. It is crucial to assess whether these specifications are realistic given the limitations of the circuit design.

Imagine you are planning a road trip. You need to know how far you want to go (output swing), how fast you'll be driving (voltage gain), and how much fuel you have (input impedance) to decide how to pack and what route to take.

Now, you must be careful here in our circuit analysis we already have seen that out of this common gate amplifier, what are the achievable performance we do have? So, if the specification the requirement if it is well within that the achievable performance of the circuit, then only a week this exercise is meaningful.

It's important to evaluate whether the desired performance specifications fall within the achievable limits of the Common Gate Amplifier. For instance, if you require a voltage gain of 50, but the design's practical capabilities can only provide a maximum of 10, then any analysis conducted would not be relevant. Thus, understanding the controllable parameters is key before moving forward.

Consider a race car driver wanting to achieve a lap time that is far beyond the car's capabilities. Conducting practice laps to perfect their driving would be pointless if the car underperforms at that level.

So, to start with let me consider that output swing it is see if this is 12 V and the requirement maybe a ± 4 V; which means that the requirement is 8 V P-P how do you how do you utilize this information?

The calculation begins with establishing the necessary output swing based on the system’s specifications. If the power supply is 12V, and we require an output swing of ±4V, this leads to a total peak-to-peak output swing of 8V — this is critical for determining how much voltage drop is permissible across the active components in the circuit.

Think about a water tank. If the tank can hold a maximum of 12 liters, and you want to drain 4 liters, this leaves you with just enough space for an 8-liter flow before you hit your limit.

So, if the output voltage it is changing from it is quiescent voltage by an amount of say 4 V towards the ‒ve side then we have to ensure that the device it is in saturation region. Which means that the DC voltage here at the output it should be such that DC voltage here and DC voltage at the gate it should be such that the V should be at least 3 V.

To ensure proper operation of the amplifier, understanding DC voltage levels is essential. If the output is swinging negatively by 4V, the gate voltage must remain sufficiently below a certain threshold (in this case, at least 3V) to place the transistor in the saturation region, where it functions optimally.

This is similar to making sure that a roller coaster does not drop too low on its track. If the threshold level for safety is 3 feet above ground, the roller coaster needs to maintain a height above that for a smooth ride.

Here we can say that this drop it is ah. So, here we do have 3 V remaining 9 V here and there is no current flowing here. So, we can say drop across R it is 3 and a drop across a R it is 1 unit.

With known voltage drops across components, we can start formulating the necessary resistor values for the overall circuit. For example, if the voltage drops across resistors are split such that one resistor drops 3V while the other drops 1V, we can calculate their respective values based on the required thresholds to ensure proper functioning of the Common Gate Amplifier.

This can be likened to splitting a pizza among friends. If one person gets 3 slices and another gets 1 slice, you can determine how large the pizza should be based on how many slices in total you want everyone to enjoy.

Now what we obtain here it is end of this analysis what you obtain here it is the R = say 200 k and then R it is 100 k, then R it is it is . So, it means 1.25 kΩ and then R it is 250 Ω.

At the conclusion of the analysis for the Common Gate Amplifier, the component values have been determined: for example, resistor values could be finalized at 200kΩ for R_A, 100kΩ for R_B, and 250Ω for R_input. This ensures that the amplifier meets the identified requirements regarding voltage gain, output swing, and input impedance.

This is similar to constructing a bridge. Once you finalize the measurements of each component based on safety standards and traffic requirements, you can proceed to build the structure confidently knowing it meets all needs.

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