61.6.7.2. Output Impedance

So, this is the output port and R which is R coming in parallel with whatever the resistance coming out of this entire circuit. So, if I want to know what will be the resistance of this circuit the circle circuit what it can say that this r and r, they are coming in parallel this one of course, I have to make the signal = 0. So, that makes this = 0. So, we can ignore that part.

In this chunk, we start by identifying what the output impedance of the circuit is. The output impedance is mainly determined by how the resistance from the output port interacts with other resistances in the circuit. It is stated that the load resistance, R, is in parallel with the other resistance components (denoted as r). We can determine the total output impedance by knowing these components. By setting the signal to zero, we can simplify the analysis because it allows us to ignore certain paths or components that do not contribute to the output resistance at that instant.

Think of output impedance like a water tap. The flow of water (signal) coming out of the tap depends on the size of the hose (resistance) connected to it. If you connect a wider hose (lower impedance), more water can flow through (higher output), but if the hose is narrow (higher impedance), less water flows. By measuring how the tap behaves when you block some of the hose, you get an understanding of how it works without interference.

To know this resistance what we can do? We can draw the rest of the circuit to get the equivalent resistance. So, we do have r and then we do have g v and at this node at this node we do have r connected to ground and also we do have r connected to ground.

Here, we proceed to calculate the equivalent output resistance by analyzing the connection of different resistive components within the circuit. The circuit can be visualized by drawing it out, and we see that the output resistance can be determined by looking at the arrangement of several resistors, including the resistances denoted as 'r' and 'g v'. The critical operation here is to measure how these resistances connect and their resulting effect when considered together, which can produce a comprehensive understanding of the output at this node.

Imagine you're trying to find how many straws you need to use to drink a thick smoothie. Each straw represents a resistor, narrowing down your options. Some might be thicker (smaller resistance), while others are thinner (greater resistance). By looking at all the straws laid out together, you can determine which combination will let you sip your smoothie the easiest, simulating how those resistances interact in the circuit.

In fact if you see here compared to this part and this part; this is quite high. So, we can approximate that this is g r (r ⫽ r), which means that the output resistance coming here it is quite big and it is expression it is given here.

This chunk goes into the mathematics behind calculating the output resistance. The speaker indicates that certain resistances can be approximated as contributing significantly more to the total resistance. The output resistance can thus be simplified to a formula involving g, r, and their combinations. This is important for understanding how the output resistance is not just a simple sum of resistances, but rather a product based on their arrangement in the circuit.

It's like estimating how much weight you can balance on a see-saw. If you place a heavy object on one side, you can approximate that side's weight affects the balance disproportionately compared to the other side where lighter objects are placed. Similarly, when calculating output resistance, some resistances dominate the total picture, allowing us to simplify the analysis.

In fact, if you see these two transistors while these two transistors are connected in series and if the gate of the first transistor is connected at a certain point.

This final chunk discusses the practical applications of the output impedance calculated from the circuit analysis. It emphasizes that the arrangement of the transistors (series connection) and the designated points for connections are crucial in determining how effectively the circuit will operate. It highlights the importance of these factors in practical scenarios, ensuring that the desired output performance can be achieved in real applications.

Consider a team of runners in a relay race where each runner hand-offs the baton. If one runner (transistor) doesn't pass the baton properly or runs out of sync, the entire team's performance suffers. Similarly, how the transistors are connected and interact with each other in the circuit is critical in ensuring the circuit functions efficiently and effectively.

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