67.7.1. Bandwidth and Gain Trade-off

Yeah. So, welcome back after the short break. And we were discussing about the limitation of the voltage gain of the common emitter and common source amplifier particularly if it is having passive load. And intuitively we understand that, how it can be enhanced...

This chunk begins by addressing the voltage gain limitations of common emitter and common source amplifiers, particularly when using passive loads. The speaker emphasizes that while it is intuitive to consider ways to enhance gain, simply using any arbitrary active load may actually hinder performance. The example illustrates that increasing the slope of the load line characteristic without proper consideration can lead to reduced gain instead of the desired increase.

Think of a sports team that is performing poorly. Simply changing the position of players without understanding their strengths can lead to worse performance. In the same way, using an inappropriate load can reduce the amplifier’s effectiveness.

So, let us see what kind of implementation we can think of to get this kind of non-linear load line, particularly this one which is giving us the gain. So, in the next slide we do have common source amplifier with active load...

In this segment, the discussion shifts to the implementation of a common source amplifier using an active load—the PMOS transistor. The configuration is described where one transistor's source connects to a DC voltage, and its gate controls the drain current. This method aims to achieve higher gain by establishing a specific characteristic load line. It highlights the importance of setting correct biasing to ensure both transistors operate in the saturation region, leading to optimal performance.

Imagine a teacher who wants to ensure all students are engaged. If the teacher can't gauge how each student's understanding aligns, they can’t effectively adjust their teaching methods. Similarly, ensuring the correct configuration of transistors is vital for maximizing the performance of the amplifier.

Now naturally, then who defines this current? For proper operation, we require both the current should be equal and we need to satisfy some condition to ensure that I and I; I rather I they should be equal...

Here, the importance of current equality between the transistors in the saturation region is discussed. For optimal transistor operation, it must be assured that the currents through the devices are equal. The section emphasizes that if this condition is not met, one transistor could fall into the triode region, harming the overall gain. Thus, understanding this balance is crucial in amplifier design.

Imagine running a relay race where each runner needs to maintain the same speed to hand off the baton smoothly. If one runner slows down, the entire team's performance suffers. Similarly, the equality of currents ensures both transistors work in harmony for better amplifier gain.

So, again to come back to the basic operation of the device particularly for M1, we do have I versus V characteristic curve and this is beyond threshold this is square law...

This segment discusses the I-V characteristics of a transistor and how they relate to determining the load line for the amplifier configuration. The load line intersects with the transistor's characteristic curve, and understanding this intersection is vital for estimating output behavior for varying input signals. The discussion includes how to graph these characteristics and the implications of slope changes on circuit performance.

Just as you might plot your monthly expenses against your income to determine a budget surplus or deficit, plotting the I-V curves helps visualize how far an amplifier can reach in terms of output voltage based on its configuration.

So, in summary what do you obtain here it is that, because the load line slope, it got changed compared to the earlier slope...

In this concluding segment of the section, a summary of insights regarding gain versus bandwidth trade-offs is presented. It explains how changes in load line slope due to the transition from passive to active loads result in an increase in gain but a simultaneous decrease in bandwidth. This trade-off highlights the balance engineers must consider when designing amplifiers.

Imagine trying to balance a scale where adding weight on one side (more gain) causes the other side to rise (decreased bandwidth). This illustrates how optimizing one aspect of amplifier performance can unintentionally impact another.

--