58.2.2. Small Signal Performance of CC Stage

Now, with this information we can find the value of the small signal parameters namely g. In fact, let me complete this part and then I will be coming to the small signal parameter. So, we do have I = 2 mA then drop across R = (2 mA × R it is 3.3). So, that gives us V = (12 V ‒ 3.3 × 2) which is 5.4 V. So, the operating point it has given here and based on this operating point we can now calculate the small signal parameters value namely g = and this is ℧ and then the r which is . So, that = 1.3 kΩ and then r it is . So, that = , 50 kΩ.

In this chunk, we compute small signal parameters based on the operating point of the transistor. The collector current (I) is found to be 2 mA using the drop across a resistor (R). We calculate the voltage at the collector (V) and find it to be 5.4 V. Using this V, we can determine small signal parameters: transconductance (g) and output resistance (r), which are essential for analyzing how the circuit reacts to small signals.

Imagine you are adjusting the height of a swing by pulling on the chains. The height of the swing corresponds to the voltage (V) while how directly you can influence that height with your grip relates to transconductance (g). The swing’s flexibility and how much it can support your weight without collapsing is similar to output resistance (r).

So, now we obtained the small signal parameters now we can get the voltage gain. So, voltage gain it is g (R ⫽ r ). So, the g we have and R it is 3.3 k ⫽ 50 k. So, probably you can approximate this by 50 or probably you can calculate these parallel resistances together and then you can find what the output resistance is.

In this stage, we calculate the voltage gain of the common collector (CC) stage using the transconductance (g) and the resistances in the circuit. The gain formula considers the output resistance (R), resulting from the combination of a couple of resistors. By calculating the voltage gain, we gain insights into how effectively the CC stage amplifies signals.

Think of the voltage gain like a team of workers building a house. The lead engineer's ability to manage different tasks (g) directly impacts the speed of the construction (voltage gain). The available tools (R) and materials are akin to resistances that either enable or slow down the work depending on how well they are combined.

So, this is the; this is the exact statement of the problem we have address earlier. Now, for our main focus to demonstrate how the bandwidth it will be extended we can probably calculate only the upper cutoff frequency using whatever the information we do have...

The cutoff frequency signifies the point beyond which the amplification from the circuit starts to decrease and is essential for understanding bandwidth. It is programmatically calculated from the resistances and capacitance in the circuit. The upper cutoff frequency determines the range of frequencies the amplifier can handle effectively without significant loss in gain.

Consider a water pipe where water flows through at different speeds. The upper cutoff frequency relates to the pipe's diameter; if the pipe is too narrow, water (analogous to signals) cannot pass through quickly, leading to a drop in flow (voltage gain) beyond a certain speed. A wider pipe can accommodate faster speeds up to the frequency limit, analogous to better bandwidth.

So in summary what we have circuit performance why should you have the circuit gain is 238 and then the upper cutoff frequencies 513 kHz. Now, the exercise we are going to do it is that we are going to put in this case instead of putting the capacitor here we can probably directly put a CC stage here...

The analysis demonstrates that adding a common collector stage enhances the circuit's bandwidth. By measuring performance differences with and without this stage, we observe changes in both gain and frequency range. This addition is aimed to improve circuit response and functionality across a broader range of frequencies.

Imagine attaching an extra section to a water slide that allows more water to flow through more rapidly. When we enhance the structure (adding the CC stage), water (signals in the circuit) moves more smoothly and swiftly across a wider range of flow rates, enhancing the overall experience (bandwidth).

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