53.2.5. Output Impedance Analysis

Now, if I remove the C what will be the consequences on these two important parameters namely the input resistance and the voltage gain and maybe the output impedance also so, that is what we are going to discuss now.

In this section, the focus is on how removing the capacitor (C) affects the output impedance, as well as the input resistance and voltage gain. The discussion lays the groundwork for understanding the output characteristics of the common base amplifier when the capacitor is absent.

Think of the capacitor as a water gate that allows a smooth flow of water into a tank. If you remove the gate, the flow becomes irregular and restricted. Similarly, removing the capacitor affects how the signal is processed, leading to changes in output parameters.

So, let me draw the small signal equivalent circuit, small signal equivalent circuit of the main amplifier, try to explain that what kind of effects are there. This is R connected to AC ground...

The small signal equivalent circuit depicts how the amplifier behaves under small input signals. In it, resistors and capacitors are represented to analyze how input signals affect the output. This helps in understanding how voltage and current vary in response to input fluctuations, even when the capacitor is not present.

Imagine you are tuning a radio. The small signal equivalent circuit is like the radio's internal wiring that determines how well you pick up stations. The better the connection and components, the clearer the sound—similarly, good small signal characteristics allow the amplifier to respond well to signals.

If we have v here and the voltage available across this r it is nothing, but the potential division of whatever the voltage you do have.

Here, the text explains how to calculate the voltage gain in terms of the input voltage across the resistor. The relationship between voltage across components helps determine how much the signal is amplified, showing the connection between component values and overall gain.

Think of this like a set of stairs. If the stairs are steep (high gain), you rise quickly, but if they are flat (low gain), you rise slowly. The voltage gain describes how steeply the amplifier steps up the input signal to an output level.

So, what we said is this g will be replacing by ( ). So, from that we can say that input resistance R if I ignore R and if I consider .

The removal of the capacitor dramatically affects the input resistance of the circuit. When considering how components are arranged, we find that the input resistance changes based on what remains in the circuit, illustrating why maintaining certain components is crucial for ideal amplifier behavior.

Imagine a traffic signal controlling cars at an intersection. The signal allows cars to pass smoothly (representing high input resistance). If the signal fails, congestion occurs (representing low input resistance). Similarly, input resistance needs to be optimal for smooth functioning.

If we are not using this C, then the input resistance it is quite large now compared to if I use C .

This part emphasizes the substantial differences in performance metrics such as input resistance and voltage gain when the capacitor is not included. It concludes that omitting the capacitor leads to a significant change, which highlights the importance of this component in maintaining performance levels.

Consider a sponge that soaks up water. When the sponge is dry (no capacitor), it holds little water (high resistance). When it’s wet (capacitor in place), it can absorb much more (low resistance). This analogy helps visualize how components affect circuit performance.

So the input impedance and voltage gain they are getting affected by a factor of 10. So, that is about the common base amplifier...

The conclusion summarizes the findings on how omitting the capacitor can lead to a tenfold degradation in input impedance and voltage gain. This underscores the necessity of including appropriate capacitors in circuit design to ensure optimal function of amplifiers.

This is akin to a quality chef who has specific tools at their disposal. Without important tools (like the capacitor), the chef's ability to prepare a dish diminishes greatly, which parallels the drop in performance when capacitors are missing in amplifiers.

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