64.3. Change in R

So far what we have discussed that the advantage of cascode amplifier with respect to standard CE amplifier namely what you have seen is that in case if you are retaining this passive element for both the cases, then gain wise we do not get much advantage. But then what we have seen is that in case if we have the input resistance and the source resistance together forming a significant significantly low frequency pole due to this large value of the C , then we have seen that the cascode amplifier is giving some advantage.

This chunk introduces the benefits of using a cascode amplifier compared to a standard common-emitter (CE) amplifier. While the gain may not drastically improve when passive components are retained, the cascode amplifier significantly enhances low-frequency performance due to its increased input and source resistance, which together create a low-frequency pole. This allows the cascode amplifier to maintain better performance at low frequencies, which is vital for certain applications where signal integrity at low frequencies is important.

Think of the cascode amplifier as a car with a turbocharger. A standard car (the CE amplifier) performs adequately but lacks speed and efficiency at high speeds. When you add a turbocharger (the cascode configuration), the car (amplifier) can better handle higher speeds (higher frequencies) without losing stability, similar to how the cascode amplifier maintains performance at lower frequencies by managing resistance well.

In fact, cascode amplifier it is having two types of advantages; one is extending the bandwidth as we just now we have discussed particularly in presence of significantly large value of the source resistance, the other advantage which is commonly used is that the increasing the gain drastically.

The chunk discusses two primary advantages of employing a cascode amplifier: extending the bandwidth and drastically increasing gain. By using larger values for the source resistance, the bandwidth is enhanced, allowing the amplifier to handle a broader range of frequencies effectively. Additionally, the design of the cascode amplifier allows for a significant increase in gain, making it more effective for applications that require amplified signals without distortion.

Consider a water pipe system. A regular pipe represents a basic amplifier. If you increase the pipe size (like increasing the source resistance), more water can flow through, improving efficiency (bandwidth). If you add a pressurized pump (cascode configuration), you not only enhance water flow but also increase the pressure significantly (gain), allowing the water to reach further distances effectively.

So, to demonstrate the capability of the cascode amplifier to increase the gain first of all let we consider a different situation instead of having this R if you put some active circuit there, probably then the advantage of the cascode amplifier particularly for enhancing the gain it will be quite prominent.

This chunk suggests using an active circuit in place of passive components to see the dramatic effects that a cascode amplifier can have on gain. By replacing passive resistors with active circuits, like current sources, the amplifier can achieve higher gain, showcasing its superior performance characteristics in practical applications. The use of active circuits helps in maintaining the desired impedance levels and allows the amplifier to operate more efficiently.

Imagine a sports team that usually practices by running laps (passive). If the coach introduces strength training sessions (active circuits) focused on different muscle groups, the team's overall performance and speed will improve significantly during games (increased gain), demonstrating how targeted training can enhance capabilities. Similarly, using active components in amplifiers boosts their performance.

So, what you are expecting from the lower side as we have discussed based on the resistance here based on the R and R, the current flow here quiescent current flow here it is 2 mA, the voltage here it is 0.6 V DC the voltage here it is 1.2 V.

In this part, the discussion revolves around the expected output voltage based on the resistance values present in the circuit. With a quiescent current of 2 mA, and given the relationships between resistance, voltage, and current (Ohm’s Law), we can predict output voltages at certain points in the circuit. This information is crucial for understanding how voltage is distributed and how the design can affect overall performance.

Consider a household electrical system. If you have multiple devices (representing the circuit components), each device will need a specific voltage to operate effectively. Much like how you would allocate different power sources to ensure everything works (current flow), engineers must calculate how voltage splits in amplifiers based on resistances to ensure optimal functioning.

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