66.2.4. Practical Circuits Having the Active Load

Compared to our overall weekly plan we are in week-6, I should say module-6 and we are. In fact, we already have completed these two sub topics namely Multi Transistor Amplifiers and then Cascode amplifiers. And today we are going to talk about Amplifier with active load. In fact, incidentally when we talk about active load, the amplifier it is having multiple transistors.

In this chunk, we are introduced to the concept of amplifiers with active loads. The speaker highlights that they are transitioning to a new topic after discussing multi-transistor amplifiers and cascode amplifiers. Active load amplifiers are important in the context of circuits that use multiple transistors. Active loads replace passive loads with components that use transistors, which allows for better performance in amplifying signals.

Imagine a factory that produces toys. If the factory has limited workers, it can only produce a small number of toys (passive load). However, if they install automated machines (active load) that can work continuously without rest, production can significantly increase. Similarly, active load amplifiers allow more efficient signal amplification by using transistors to replace passive components.

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. Then, from that we will 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 or maybe intuitively explaining the gain.

This chunk sets the agenda for the session. The primary focus is on understanding why active loads are preferred in amplifiers. By starting with the motivation for using active loads, the speaker aims to explain the enhancements in amplifier performance, including how their operation and circuit analysis can lead to improved gain. The discussion will delve into specific concepts such as small-signal models, which are essential for understanding how these amplifiers behave under practical conditions.

Think of the motivation for using active loads as upgrading from a bicycle to a motorcycle for deliveries. The bicycle (passive load) can deliver some packages but is slow. Switching to a motorcycle (active load) allows faster delivery of packages, maximizing efficiency. This improved performance in amplifiers similarly enhances the ability to handle signals.

So, this is a recapitulation or recalling whatever we know about CE amplifier and not only we will be talking about CE amplifier. But basic operation of the CE amplifier just to see that, what is it is limitation of the voltage gain.

In this chunk, the speaker reflects on common emitter (CE) amplifiers and their performance limitations. By recalling the specific aspects of CE amplifiers, the speaker aims to outline the boundary conditions under which these amplifiers operate. Identifying these limitations is crucial because it sets the stage for understanding how active loads can resolve these issues, particularly in terms of voltage gain.

Consider a well-engineered bridge that can support a specific weight limit (voltage gain). If too many heavy trucks (signals) cross it, the bridge may fail (gain is limited). By using reinforced materials (active loads), we can increase the bridge's capacity, allowing it to support heavier loads effectively.

So, now if we want to really increase the gain, of course it is having a limitation of the gain will be talking about that also. If you numerically see what is the value here, if you put the expression of g into this equation that gives us that is I quiescent current.

This chunk dives into mathematical perspectives on increasing amplifier gain. By expressing gain in terms of quiescent current, the speaker reveals the relationship between an amplifier's static state and its ability to respond to dynamic inputs. These mathematical insights reveal the need for a deeper understanding of current control in amplifying devices, encouraging the use of active loads to achieve higher gains.

Think of a heat lamp in a cold room. Keeping it at high wattage (quiescent current) allows it to efficiently warm the space (increase gain). However, if the wattage was restricted, the room would remain cold. Thus, understanding this relationship can help us design better heating systems, akin to designing amplifiers.

Similarly, if you look into the common source amplifier on the other hand it is philosophically it is same, only thing is that the I-V characteristic instead of I versus V , now we have to I versus V .

In this chunk, the speaker compares the common emitter (CE) amplifier with the common source (CS) amplifier. Both types have similar fundamental principles but differ in their configurations and characteristics. Understanding these differences is vital for students to apply the right amplifier type in practical circuit design.

Imagine two types of cooking methods: baking and grilling. Both cook food but do so uniquely. Grilling uses direct heat from below (common emitter), while baking envelops the food in hot air (common source). Recognizing when to use each method is essential for obtaining the desired cooking outcome, just like choosing the right amplifier for the task.

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