54.2.3. Calculating Output DC Voltage

So, let us 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 utilize this information?

In this chunk, we start by defining the output swing for the amplifier. The setup has a total supply voltage of 12 V and an output swing requirement of ± 4 V. This means the total peak-to-peak swing (P-P) must be at least 8 V, allowing the output voltage to fluctuate 4 V above and 4 V below a quiescent point. When analyzing amplifiers, it's essential to ensure that the circuit can handle these voltage swings without clipping, which occurs when the amplifier reaches its maximum output capability (i.e., the voltage exceeds the supply voltage or drops below ground).

Think of the output swing like a swing set. If you want to swing to the highest point, the swing must have enough space to go up and down without hitting the ground. Similarly, in electronics, the output swing must fit within the limits set by the power supply.

The first step it is that the voltage drop across this resistance, it should be more than 4 V to ensure the positive swing of the output voltage is at least 4 V.

To achieve the desired output swing, it's crucial that the voltage drop across the load resistor in the amplifier's output stage is significant enough. Specifically, we need more than 4 V across this resistor to guarantee that the output voltage can swing up to its maximum value. If this voltage drop is less than 4 V, the positive cycle of the output signal will get clipped, leading to reduced performance of the amplifier.

Imagine a water slide. For the slide to function effectively, there needs to be enough slope (or voltage drop in this case) so that the water can flow all the way down without getting stuck. If there isn't enough slope, water will pool at the top instead of sliding down.

On the other hand, the gate voltage of this MOS transistor should be sufficiently low to ensure that the device is in the saturation region.

For a MOSFET to operate effectively in the desired region (the saturation region), where it provides linear amplification, its gate voltage must be low enough to maintain this condition. If the gate voltage is too high, the MOSFET may enter cutoff, which halts conduction, or into the triode region, which limits amplification. This balancing act between the gate voltage and drain voltage is critical to maintain the amplifier's performance range.

Think of this situation like adjusting the volume on a speaker. If the volume is too low (acting like a high gate voltage), you can't hear anything (cutoff). If it's too high, the sound distorts (triode region). The goal is to find that sweet spot in the middle where the sound is clear and loud—the active region of the MOSFET.

Let you consider VOUT DC voltage it is say we consider a drop of 5 V so, 12 – 5 so, that is 7 V.

In this step, we assume that after accounting for the required voltage drop across the output resistor, the remaining voltage (7 V) is the quiescent output DC voltage level of the amplifier. This is crucial because it sets the baseline from which our output swing will occur. If this DC voltage level is set correctly, we ensure that the amplifier can effectively swing both positively and negatively without clipping at either end.

Consider a battery-powered toy. If the toy runs on a battery providing 12 V, and the toy has components that require 5 V to function properly, the toy will need the remaining 7 V for additional circuits. This remaining voltage must be monitored just like we monitor the DC output voltage to ensure proper function.

We can say that this drop it is 3 V remaining, 9 V here and there is no current flowing here. So, we can say drop across RA it is 3 V and a drop across RB it is 1 unit.

Having established the necessary voltage levels, we now focus on determining the resistance values needed to achieve these voltage drops. Given the output voltage and the supply voltage, we derive a relationship between the resistors RA and RB. From the calculated drops, we can determine the ratio of these resistors, which will influence input and output impedance, as well as the performance characteristics of the amplifier.

It's like mixing paint colors to achieve a desired shade. If you know how much of each color you need (the voltage drops across the resistors), you can mix the correct amounts (resistor values) to achieve that shade (the desired amplifier performance).

Next thing is that you must be having the requirement of the input impedance which is given to us that this is a 250 Ω.

Input impedance is a critical parameter that determines how much the amplifier will load the previous stage in the signal chain. In this case, if the desired input impedance is 250 Ω, we have to choose the resistor values accordingly to achieve this. This ensures that the amplifier can interact correctly with other components without causing signal loss or distortion.

Think of it as the entrance of a concert hall. If the entrance can accommodate enough people (input impedance), it won't cause bottlenecks (signal loss). If too few people can enter at once, there will be delays and the overall experience will be affected.

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