66.2. Overview

Dear students welcome back to NPTEL online certification course on Analog Electronic Circuit. Myself Pradip Mandal from E and EC department of IIT Kharagpur. So, to continue this course today’s topic of discussion it is Amplifier with Active Loads.

In this chunk, we are introduced to the topic of amplifier circuits that utilize active loads. An active load amplifier differs from traditional amplifiers because it replaces passive components with active devices such as MOSFETs or BJTs. These active components help manipulate the circuit’s gain and performance in a unique way.

Think of an active load amplifier like a restaurant that uses a food critic instead of just a menu to enhance the overall dining experience. The critic (active load) has the expertise to influence the meal's outcome (amplifier performance), elevating it beyond what the standard menu (passive load) could achieve.

In fact, when we talk about active load, the amplifier is having multiple transistors. So, you may say that this is also a special kind of multi-transistor amplifiers. But we like to explicitly say that it is having unique characteristic.

The motivation for using active loads revolves around improving the performance of amplifiers. Traditional setups using passive elements can struggle with limitations—most notably in voltage gain. By employing active loads, we can enhance these characteristics significantly, allowing for more versatile and powerful amplifiers.

Imagine you’re at a sports game. A team with only basic players (passive load) may have difficulty scoring, whereas a team with skilled players (active load) can adapt, outmaneuver opponents, and improve their chances of winning (higher gain and performance).

Now, today what we are planning to cover it is under this active load amplifiers, we do have to start with we do have motivation of using this active load.

Active load amplifiers begin with understanding their basic operation. These kinds of amplifiers utilize transistors as loads instead of resistors, which provides not just a location for current flow but also increases the overall gain. The change of loads allows the designer to better manipulate the amplifier's output in a more controlled and efficient manner.

Using an active load is like having an adjustable fan in a car. When the fan operates at a higher speed, it improves engine efficiency and cooling (similar to improved gain in amplifiers). Conversely, traditional fans are fixed and cannot adjust to optimize performance.

We will be talking about basic operation of amplifier having active load and their corresponding circuit analysis including, small signal model and then finding the gain.

This chunk focuses on circuit analysis of amplifiers with active loads. It covers how to analyze these circuits using small-signal models, which help in predicting their behavior under varying conditions. This is crucial for design, as it allows engineers to determine the gain and performance characteristics essential for applications.

Analyzing active load circuits is akin to tuning a musical instrument. Just as musicians make adjustments to perfect the sound quality (gaining optimal performance), engineers tweak circuit parameters to achieve the desired electrical responses.

We will be talking about practical circuits having the active load and for both the basic operation as well as for practical amplifiers.

The summary includes not only the theoretical aspects but also practical applications of active load amplifiers. Engineers will also be presented with design guidelines to create effective circuits that take advantage of active loads for higher efficiency and better performance in real-world scenarios.

When constructing an efficient building, architects can design around structural supports (active loads) to ensure stability. Similarly, in amplifier engineering, the right design ensures the circuit meets practical needs while still optimizing performance.

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