58.2.4. Calculating Bandwidth with CC Stage

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 and rest of the things we will be keeping same.

This chunk discusses the overall performance of the circuit before introducing the Common Collector (CC) stage. The circuit has a gain of 238 with an upper cutoff frequency of 513 kHz. The objective is to enhance the bandwidth of the amplifier by replacing the coupling capacitor with a CC stage, which is expected to provide a wider bandwidth while maintaining the previously established gain.

Think of this like upgrading a car's engine. Initially, the car can only go up to 60 mph (representing the bandwidth of 513 kHz), but by adding a more powerful engine (the CC stage), you could potentially increase the car's maximum speed (bandwidth) while still allowing it to achieve great fuel efficiency (gain of 238).

If I say that we do have a 5.4 V DC. So, that is 5.4 V along with it is Thevenin equivalent resistance which is R. So, that is 3.1 kΩ that is coming to the base of transistor-2 and the transistor-2 emitter of transistor-2 it is connected to ground through this R and R.

This chunk explains how to determine the operating point for the CC stage. The DC voltage of 5.4V is applied to the base of transistor-2, and its emitter is grounded through the resistances, which influences the voltage and current flowing through the transistor. Knowing this helps characterize how the transistor will behave in the circuit, particularly regarding how it will amplify signals.

Consider a water pipe system. The water pressure (voltage) and the diameter of the pipes (resistors) determine how much water can flow where. Here, 5.4 V acts like the pressure pushing water through various pipes (transistors), which impacts the system's overall performance.

What is the expression of the gain of the CC stage? If I call this is A gain voltage of the second stage if of course, it will be very close to one that is the anticipation.

This segment covers the voltage gain of the CC stage, which is expected to be close to unity (1). This means the CC stage is designed primarily for impedance matching and not for amplifying signals significantly. The gain can be engineered to precisely account for the signal load, ensuring effective transfer of voltage from one stage to the next.

Imagine a relay team in a race. Each runner (the stages) passes the baton (the signal) to the next runner, aiming to keep the baton speed as near the same as possible. The CC stage ensures the baton is passed efficiently without losing speed (signal strength), making it easier for the next team member to run effectively.

Now, next thing is that how the CC stage it is enhancing the bandwidth. So, how do we calculate the bandwidth first of all we have to see the corresponding g.

In this section, the focus shifts to how the CC stage enhances the amplifier's bandwidth. The bandwidth indicates the range of frequencies over which the amplifier can operate effectively. The parameters such as the transconductance (g) and the resistances present in the circuit are crucial for determining the cutoff frequencies, both lower and upper.

Think of bandwidth as the size of a highway. A wider highway (increased bandwidth) allows more cars (signals) to travel without congestion. Just like adding additional lanes or optimizing traffic flow to accommodate more vehicles, the CC stage is designed to increase the amplifier's capacity to handle a broader range of frequencies without distortion.

In summary we can say that if the original CE amplifier it is having a frequency response like this. So, it is having a gain. So, this is A in dB and this is frequency in Hz in log scale and this one was 513 kHz was the upper cutoff frequency. Now, by adding this CC stage what we have here it is the gain got slightly decreased, but then bandwidth got extended.

This concluding chunk provides a comparative summary of the amplifier's performance before and after incorporating the CC stage. While the gain slightly decreases, the bandwidth experiences a significant enhancement, achieving up to 10 MHz. This illustrates a successful trade-off in amplifier design: prioritizing bandwidth extension while sacrificing only a small amount of gain.

This situation is akin to a bakery that increases its oven size to bake batches of bread faster (wider bandwidth) but may not be able to produce quite as many fancy pastries (slight gain reduction). The overall output may change slightly, but the improvement in efficiency and quantity is significant, leading to better satisfaction for customers (the consumers of the signals).

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