67.1.2. Output Resistance Considerations

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.

This chunk discusses the role of resistor R in providing negative feedback in a circuit configuration. By connecting R to the output, it feeds information about the output voltage back to the base of a transistor. Negative feedback is crucial because it stabilizes the operating point, allowing the circuit to reach steady functioning levels smoothly.

Think of it like a thermostat in your house. The thermostat monitors the temperature and sends signals to adjust the heating system. If the room gets too hot, it turns down the heat, providing a feedback loop that keeps the temperature stable.

However, at the same time there is a chance that this R ; it may feed the signal back to this transistor and it may reduce the gain of the circuit. To avoid that, we put some extra capacitor here.

This part notes that while negative feedback is beneficial, it might also result in reducing the overall gain of the circuit. To counteract this potential loss of gain, an additional capacitor is introduced into the configuration. This capacitor allows signals to flow while blocking undesirable feedback that would lower the gain.

Imagine you’re trying to enhance your voice while singing in a big hall. If someone keeps trying to correct your pitch (feedback), it could actually make you sing worse. To avoid them affecting your performance negatively, you could wear noise-canceling headphones to focus on your voice without distractions.

So, if you consider it is a small signal equivalent circuit which is shown here in the next slide...

Here, the section transitions to discussing a small signal equivalent circuit. This is an important model in electronics used to analyze how circuits react to small fluctuations around a DC operating point. The text implies that a visual representation of this concept will be provided in the next slide, which would help students better understand the theoretical underpinnings.

Think of this equivalent circuit as a simplified drawing of a city map focusing only on the main streets rather than every tiny detail. It helps you find the best route without being overwhelmed by the entire city's layout.

So, the output resistance it is not only r and r coming in parallel. In fact, ... output resistance it is drastically getting reduced from whatever our original target of r ⫽ r only that will drastically that may affect the gain.

This portion highlights the complexity in calculating the output resistance of the circuit, stating that it is influenced by various resistances that are arranged in a parallel configuration. If the output resistance is significantly reduced from its expected value, it can lead to reduced gain in the circuit, which has implications for performance. It stresses the importance of careful consideration in the design.

Imagine you have several water pipes coming together. If many of them are wide-open (low resistance), the entire flow can become too fast, causing other areas to dry up. Similarly, in circuits, if output resistance is too low, it can impact the 'flow' of electrical signals, reducing effectiveness.

And that makes this circuit going back to the previous one except of course, this R it will be coming in parallel.

This section concludes that by incorporating the capacitor into the circuit, the configuration can revert to a more favorable condition where the gain remains high. By grounding one part of the circuit through the capacitor, it prevents negative feedback while still allowing the output to interact with resistances appropriately.

Consider a train on a track. If you put a large buffer (capacitor) between two rail cars, it can absorb shocks and prevent interruptions in movement, allowing the train to run smoothly without losing speed due to disruptions.

So, in summary of this modification what we like to say here it is...

This conclusion succinctly wraps up the key points discussed in this section. It reiterates how connecting the resistor affects circuit performance and the potential adverse impacts of feedback on gain. It also sets the stage for further exploration of practical applications and numerical examples in the following classes.

Think of it as the end of a chapter in a book. The author wraps up the main themes discussed so far, reminding you of the motifs and leaving you excited for the next chapter where more complex ideas will be developed.

--