67.3.2. Topics for Next Discussion

So, this R as it is giving the information of the output voltage to its base we may say that it is working in feedback connection. However, you need to be careful that while this R connected to the output node it is providing a ‒ve feedback to stabilize the operating point and it ensures that the operating point it is easily achieved.

In active circuit design, when a resistor (R) is connected to the output voltage, it creates a feedback loop. This feedback helps stabilize the circuit's operating point, making it easier for the circuit to function correctly. The feedback can influence the circuit's behavior, and in this case, it provides negative feedback, which helps maintain a steady output and reduces fluctuations.

Think of this feedback connection like a car's cruise control system. When you set the speed, the system constantly adjusts the throttle to maintain that speed, even when hills or wind conditions try to change it. This is similar to how the resistor helps stabilize the output voltage in the circuit.

To avoid that, we put some extra capacitor here. So, that the v voltage or v voltage of transistor-2 signal wise it remains 0. At least in the mid frequency range this additional capacitor; it ensures that this this transistor it is really working only for giving the support not for any amplification or any feedback operation in the mid frequency range.

An additional capacitor is added to the circuit to prevent the feedback from affecting the gain of the circuit. By grounding the voltage signal at the mid-frequency range, the capacitor allows the transistor to operate in a support role rather than amplifying any feedback. This ensures that the feedback does not interfere with the circuit’s intended function.

It's like having a friend who supports you at a game but doesn't interfere when you're playing. The capacitor ensures that while the transistor is there for support, it doesn't change how the main circuit performs, just like your friend cheers for you but doesn't jump into the game.

So, if you consider it is a small signal equivalent circuit which is shown here in the next slide. If we do not put this capacitor here then naturally then it will be providing one non-zero value of v as a result this current it will be flowing as a non-zero entity. Looking into this circuit this active device it will provide additional conductance.

Not including the capacitor means the feedback will result in a small non-zero voltage, which in turn allows current to flow in a way that could create unexpected additional conductance in the circuit. This could lead to a situation where the circuit does not operate optimally, affecting performance.

Imagine trying to balance a stack of books on your head while a friend keeps pushing on your head. If they press down too hard (analogous to feedback), it could throw off your balance (the circuit’s performance). The capacitor is like asking your friend to stop pushing, allowing you to keep your balance.

To avoid it is adverse effect on the gain namely the reduction of the gain we are putting this extra capacitor which is making the base node of transistor to ground and hence the corresponding gain it is remaining high.

The addition of the capacitor is crucial for maintaining the desired gain of the circuit. By connecting the base node to ground through the capacitor, we can prevent feedback from lowering the circuit’s gain, ensuring that the signal amplification performs as expected.

Think of an amplifier as a microphone with a loudspeaker. If the microphone picks up noise from the surroundings (feedback), it can distort the sound and reduce clarity. The capacitor acts like a noise-canceling feature that ensures the microphone only amplifies your voice without interference.

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