46.4.1. Output Resistance Calculation

So, let us see what will happen for the other parameters namely the output resistance and then, input capacitance and so and so and input resistance right. So, we do have let us move to the next slide to do that.

In this part of the lecture, the professor indicates a shift in focus towards the output resistance parameter of the amplifier circuit. This serves as a segue into a deeper analysis of various parameters like input capacitance, input resistance, and importantly, output resistance. These concepts are critical in understanding how a circuit responds to external conditions.

Think of output resistance like the resistance felt when trying to push water through a narrow hose. If there's too much resistance, little water flows through. Similarly, in electronic circuits, high output resistance means the circuit struggles to drive the connected load.

So, let us concentrate on the output resistance. So, we do have the same small signal model and to know the output resistance, we have to make the signal = 0 namely base terminal we are making it AC ground. We are stimulating the circuit with v and we are observing the corresponding current flowing through the circuit.

The professor explains how to properly analyze output resistance by setting the input signal to zero. This is done by shorting the base terminal (AC ground) and applying a test voltage (v) to measure how the circuit responds, which includes calculating the current that flows through the circuit components. This technique allows for simplifying the analysis and understanding how various components contribute to output resistance.

Imagine you're testing the flow of water through a pipe. By blocking one end (AC grounding), you can measure how much force it takes to push water through. This helps determine the pipe's resistance. Similarly, by adjusting the input to find output resistance in electronic circuits, we gain insights into how easily signals can pass through.

Now, if I get the impedance of this rest of these things, then the total output impedance it will be simply this output resistance coming from... the total resistance, output resistance; it is the resistance coming from this encircle part and then, r part.

Once the voltage is applied across the circuit components and the relevant current is measured, the output resistance can be calculated by using the total impedance measured from the circuit. The professor highlights that the total output resistance is a combination of multiple resistances in the circuit, including both the primary output resistance from the circuit and the resistances connected in a parallel configuration. By calculating these values, we can attain a clear understanding of how these resistors affect circuit performance.

If you consider different types of road surfaces on a path, some rough and bumpy, and others smooth, the total resistance you face while walking depends on how these surfaces combine. Similarly, output resistance in a circuit reflects the combined resistances of various components and allows us to see how smoothly a signal can flow.

Now, since we do have the r here, the total resistance, output resistance; it is the resistance coming from this encircle part and then, r part. Conclusion is that this output resistance in the order of... low.

In summarizing the output resistance discussion, the professor concludes that this output resistance is generally low, making it advantageous for amplifying signals without much loss. A low output resistance means that the circuit can drive loads effectively, ensuring that signals reach their destination with minimal attenuation or distortion.

Think of a well-maintained road where vehicles can travel quickly without significant stops (low output resistance). If the road were bumpy or had many traffic lights, that would slow down travel (high output resistance). Thus, the concept of low output resistance in electronic circuits allows signals to flow smoothly and quickly.

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