55.3. Cascading Configurations for Better Performance

Based on that merits and demerits we shall try to combine different configurations together, so that we can get overall better performance. So, let us see what is the overall plan in the next slide.

In electronic circuits, especially in amplifiers, cascading configurations means connecting multiple amplifier stages in a series. This is done to leverage the strengths of each stage while minimizing their weaknesses. For example, a single transistor may not provide enough gain or might have high output impedance. By combining different configurations, like a common emitter with a common collector, an overall amplifier can be crafted that performs better than any single configuration alone.

Think of cascading configurations like building a team of specialists where each person brings their unique skills. For example, a chef might be excellent at making desserts but not so great at cooking main courses. By having a team, the overall dinner is much better than if the chef worked alone.

So, when we say that common emitter is the main amplifier followed by the common collector. So, likewise if we have say common collector amplifier already and then whatever the output impedance is coming from the given common collector amplifier, if you want to further decrease it is output impedance you can cascade with another common collector stage, so that the overall output impedance it will be even lower than that.

Output impedance is a measure of how much a circuit resists current flowing out of it. In cascaded amplifier configurations, the output impedance of one stage can be influenced by the next stage in the series. For instance, placing a common collector stage after a common emitter can lower the total output impedance. This is beneficial because it means the amplifier can drive loads more effectively, reducing any signal loss that may occur if the impedance was too high.

Imagine you are trying to push water through a long pipe. If the end of the pipe is wide open, water flows out easily; however, if you narrow the opening, pushing water through becomes harder. In electronics, having lower output impedance is like having a wider pipe—it allows signals to flow more freely, reducing the loss.

So, conceptually again we can increase the input impedance of an existing amplifier by connecting one common collector stage at the input side.

Input impedance refers to how much a circuit resists incoming current at its input. Adding a common collector (CC) stage can significantly increase the input impedance of an amplifier. A high input impedance is desirable as it allows the amplifier to receive signals without loading down the previous stage. This means more of the original signal is maintained and less is lost to impedance mismatch.

Consider a sponge soaking up water. If you put a larger sponge at the start, it can soak up more water without overflowing, allowing more water to continue through the system. High input impedance is like that larger sponge—it ensures more of the signal is captured without interference.

So far we have discussed basic three configurations namely, CE, then CC and then CB configuration. And, we have gone through different derivations and all.

In the context of multi-transistor amplifiers, there are three fundamental configurations to understand: Common Emitter (CE), Common Collector (CC), and Common Base (CB). Each configuration has different performance metrics—like voltage gain, current gain, input resistance, and output resistance. Evaluating these metrics helps in determining which configuration best suits a specific application, depending on whether the priority is voltage or current gain, or input/output impedance.

Think of selecting a vehicle for a journey. One might choose a car (CE) for speed, a truck (CC) for carrying capacity, or a motorcycle (CB) for agility. The choice depends on the journey's needs (performance metrics). Similarly, in electronics, depending on the application's needs, we choose the appropriate configuration.

So, if you see the common emitter followed by a common collector, its purpose it is to decrease the output impedance.

Combining a common emitter stage followed by a common collector stage is a strategic way to optimize amplifier performance. The common emitter stage provides good voltage gain, while the common collector stage helps reduce output impedance. This combination enhances overall circuit functionality by allowing the amplifier to effectively drive loads while maintaining gain.

Think of a performance duo, like a singer (CE) and a guitarist (CC). The singer delivers a powerful voice (high gain), while the guitarist manages the volume levels (reducing output impedance). Together, they perform a concert that sounds great and reaches a wider audience, just like how cascading configurations work in amplifiers.

So, we can say that by looking at the value of these three important parameters we may certify whether the circuit is good or bad.

When mixing different configurations (CE, CC, and CB), we can analyze the values of voltage gain, input resistance, and output resistance to determine the circuit's effectiveness. This helps in deciding the ultimate cascading strategy that will yield the best performance based on the desired outcome, whether it's voltage or current amplification.

Choosing the right recipe for a dish depends on the ingredients you have and what you want to achieve. Similarly, when designing circuits, evaluating the performance metrics is like picking the right ingredients to ensure the final dish (or circuit functionality) is successful. Adjusting configurations is akin to tweaking a recipe for the best flavor.

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