44.3. Summary of Analysis

Now, if we rearrange this equation what we can get is ratio of that is. So, that is the output resistance. In fact, you can further simplify this is we can say that this is. And this is you can see it is a normal approximation is. So, the output resistance it is which is quite low. Now, similar kind of analysis can be done for the common collector amplifier also to get the output resistance.

The output resistance of an amplifier is a critical factor that affects performance. By rearranging the relevant equations, we can derive the output resistance value. In both common source and common collector configurations, this resistance tends to be low, which is beneficial because it allows for more efficient signal amplification and less signal loss.

Think of output resistance like a water pipe diameter. A thinner pipe (high resistance) will restrict water flow (signal), while a wider pipe (low resistance) allows water to flow freely. We want our amplifiers to have low output resistance so that they can effectively allow the maximum amount of signal to flow through.

Now, we like to get the expression of this current i and i it is having 3 components, one is the current flowing through this r which is the voltage here and then this current which is, so this is the second part.

In a common collector amplifier, the output current consists of three significant components: the current through a resistance, a dependent current source based on the input voltage, and an additional current component. Understanding these components is crucial for analyzing how the amplifier behaves with input signals.

Imagine a busy intersection where cars (currents) flow from three different streets (components). Proper management of these streets is essential to ensure a smooth flow of traffic. Similarly, managing the current components in an amplifier ensures efficient amplification.

Now, coming to the input capacitance. So, we already got the expression of the voltage gain and its magnitude is very close to 1. So, let we use that information and let we draw the small signal equivalent circuit now we are including the parasitic components...

The input capacitance of an amplifier affects how quickly it can respond to changes in input signals. By including parasitic components in our analysis, we can refine the calculations for the voltage gain, which typically remains around unity (1). This helps us determine how effectively the amplifier can handle different frequencies of input signals.

Consider a sponge soaking up water. If the sponge is too dry (high capacitance), it takes longer to absorb water (input signal), affecting the overall performance. On the other hand, a well-hydrated sponge (optimal capacitance) absorbs quickly, allowing for better performance.

So, if you see here the small signal equivalents circuit earlier this part it was open, now we do have R. And if you see this R its connection, R it is connected from this emitter terminal to the AC ground.

An analysis of a more realistic common collector circuit shows that when an additional resistance (R) is introduced, it can impact both the input resistance and the voltage gain. The presence of this resistance modifies our earlier equations, but the benefit remains that the circuit can still maintain high input resistance while keeping the voltage gain close to one.

Imagine upgrading a bridge (the circuit) to handle larger vehicles (additional R). The bridge can still support the flow of traffic effectively, ensuring that everything continues to function smoothly despite the added complexity.

So, this is the conclusion of today's discussion. What we have seen in our discussion is that common collector and common drain amplifier they are really working as a buffer in voltage mode amplification.

As we've concluded, the common collector and common drain amplifiers serve as voltage buffers, maintaining a voltage gain close to one while also possessing high input resistance and low output resistance. This makes them ideal for isolating different stages of circuits and preventing loading effects.

Think of a relay race where one runner (amplifier) hands off a baton (voltage signal) to another runner. The baton needs to be passed smoothly (voltage gain close to one) with each runner effectively receiving the baton without slowing down (high input resistance). This ensures that the race (signal flow through the circuit) continues at full speed without dropping or losing the baton.

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