61.6.2.2. Common Base and Common Collector Configurations

So, we need to basically revisit this important property of CE and CB to motivate ourselves that combining CE and CB it is giving us a better performance.

In this section, we are revisiting two common amplifier configurations: the Common Emitter (CE) and Common Base (CB). The goal of combining these two configurations is to enhance the overall performance of the amplifier system. Each configuration has its own strengths and weaknesses – for instance, while the CE configuration typically offers high voltage gain, the CB configuration is known for its low input resistance and high output resistance. By understanding how each configuration operates, we can better appreciate how they can work together to create an amplifier that maximizes their strengths.

Imagine a two-person team, where one person is very good at analyzing data (like the CE amplifiers) and the other is great at communicating that analysis to others (similar to CB amplifiers). When they work together, they can create a comprehensive presentation that utilizes both their strengths, leading to a much more effective communication of information.

This is the corresponding circuit configuration common base circuit configuration and you may recall that it is voltage gain it is quite good, but we assume that the signal source resistance is 0 and then its main property here it is that input resistance it is low, as a result it is input port it is not really good for voltage feeding.

The Common Base (CB) configuration is particularly recognized for its voltage gain capabilities, but it is crucial to note that it performs optimally under certain conditions, which include assuming the signal source resistance to be zero. One of the defining characteristics of the CB amplifier is its low input resistance, which makes it less suitable for applications where voltage signals need to be fed into it. However, this property allows the CB amplifier to effectively handle current signals, making it valuable in specific applications.

Consider the CB configuration as a water reservoir with a small inlet. While it can accommodate a lot of flow (voltage gain), the narrow entrance means that not much water can enter at once (low input resistance). Thus, it is not the best reservoir if you need to pour water in quickly (voltage feeding), but it can efficiently hold and redirect a larger flow of water once it is there (current signals).

So, if we put say performances of CE and CB together to construct a new configuration called CE-CB, then let us see what kind of performance we do expect.

When the characteristics of the Common Emitter (CE) amplifier and Common Base (CB) amplifier are combined, they form a new configuration known as the CE-CB circuit. This hybrid configuration aims to leverage the high voltage gain from the CE stage while utilizing the CB stage's favorable properties for current handling. The result is a more efficient amplifier that can handle a wider range of signals and offer improved performance metrics, such as gain and output impedance.

Think of the CE-CB configuration as a relay team in a race. The first runner (CE) starts strong, gaining speed quickly (voltage gain), while the second runner (CB) maintains that pace (current handling) and aims for a smooth finish. Together, they can cover more ground (better performance) than either could alone.

So, this current conveyor basic purpose of the current conveyor, it is taking the or rather taking the receiving the current at the low impedance port and it is delivering the current at the high impedance port.

The Common Base configuration effectively acts as a current conveyor. This means that it is designed to take in currents from an input source that has low impedance (easy for current to flow in) and deliver it to an output with high impedance (where it can be effectively utilized). This characteristic allows the CB configuration to serve as a bridge, transferring current from a source that may have limited power to a destination that requires strong and steady current flow.

Imagine a current conveyor as a postman who picks up letters from a mailbox (low impedance) and delivers them to a main sorting office (high impedance). Although the mailbox doesn’t need to be very strong (because the letters flow in easily), the sorting office needs to handle a lot of mail efficiently without getting overwhelmed. The postman ensures that the delivery process runs smoothly between both places.

Whenever in CC stage whenever we have given the input at the base and we are observing the output here and we have seen that the gain it is close to 1 and the phase also it is a phase shift is also 0 degree.

In the Common Collector (CC) stage, the input signal provided to the base results in an output that closely follows the input, with a gain near unity (1). This means the voltage output at the emitter closely matches the input voltage at the base, with no phase shift between the two signals. This property makes the CC configuration particularly suitable for voltage buffering applications, where maintaining the same voltage level while transitioning between different parts of a circuit is crucial.

Consider the CC configuration as a mirror. Just like a mirror reflects the image in front of it without any changes in size or shape (unity gain), the CC stage reflects the input voltage almost perfectly at its output. This characteristic ensures that when you ‘view’ the output (measure it), it resembles what you put in without any modifications, making it ideal for buffering scenarios.

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