75.6. Variants of Differential Amplifier

So, how do we realize this differential amplifier? There may be different possible realization of differential amplifier, but here we do have a very basic realization of differential amplifier I should say it is basic, but still it is I should say practical circuit. Many of times it is also used in actual circuit and whatever the concepts we will be discussing related to differential amplifier for that this circuits are good enough to discuss that. So, here we are showing that the realization of this differential amplifier. So, like so, this is BJT version and here it is MOSFET version.

This chunk discusses the basic realization of differential amplifiers using BJT (Bipolar Junction Transistor) and MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) configurations. The different variants refer to the structural arrangements of these components to amplify signals accurately. Differential amplifiers can differ whether they're implemented using bipolar transistors (BJTs) or field-effect transistors (MOSFETs), providing practical options depending on application requirements. The basic structure remains similar, ensuring efficient operation in various settings.

Think of a differential amplifier as a well-organized team of workers. The BJT and MOSFET represent different roles within that team. Although they may approach tasks differently, they both aim to amplify signals effectively just as team members collaborate to solve a problem efficiently.

Now coming to the other information which is also very important, that you might have seen that we do have this circuit is having two parts structurally they are identical. In fact, this R and R we want they should be equal, R we want R should also be identical.

In this chunk, the importance of having an identical structure in the differential amplifier circuit is explained. For the amplifier to function correctly, it is crucial that the components, such as resistors (R1, R2) and transistors (Q1, Q2), are equal and matched. This equality ensures that both sides of the amplifier can respond equally to input signals, which helps maintain the integrity of the differential output by canceling out common-mode signals.

Imagine a seesaw where two children of equal weight are sitting. If both kids are of equal weight, the seesaw will balance perfectly. However, if one child is heavier, the seesaw will tilt. Similarly, for the differential amplifier to function correctly, the matching of components is essential to maintain balance in signal processing.

Now, what are the different variants we do have? First of all we have seen that for common emitter amplifier instead of having passive resistored we can have active device. So, we can probably replace this passive element by 2 identical PNP transistor. So, here and here. So, as I said that they should be identical. So, and by doing that we can get higher differential gain.

This chunk introduces the concept of using active components instead of passive elements to enhance a differential amplifier's performance. By replacing passive resistors with active devices such as PNP transistors, the amplifier can achieve higher differential gains. Active devices can amplify the signals without requiring significant additional power, thereby improving the amplifier's efficiency and functionality.

Think of using a battery-powered flashlight with a dull bulb versus one with a bright LED. The LED represents an active component that provides much better illumination than a simple bulb (passive component). Similarly, in a differential amplifier, using active devices improves signal processing capabilities.

On the other hand if we consider this resistor it is role is to play to decrease the common mode gain this R it decreases not only it is working as bias circuit, but it helps to decrease the common mode gain.

In this chunk, the focus is on managing the common mode gain while designing differential amplifiers. The resistor plays a dual role: it acts as a biasing component and also helps reduce common mode gain. By doing so, it ensures that any signals that are common to both inputs are minimized, allowing the amplifier to focus on amplifying the difference between the inputs instead.

Consider a filter that removes unwanted noise from a sound system. Just as the filter prevents background noise from overshadowing the desired audio, the resistor in the differential amplifier helps eliminate common-mode signals, allowing the amplifier to maintain clarity in signal differentiation.

So, we may say that if we have a circuit like this, if we have a circuit where the load part it is active it may be having meaningful bias here and here and then of course, the main differential pair this Q and Q normally it is referred as in differential pair.

This chunk discusses the potential for further enhancements to differential amplifiers by using active load components. By implementing meaningful biases in the load components, the performance of the differential amplifier can elevate even more. This arrangement also allows for improved linearity and increased overall gain, promoting more accurate signal amplification in diverse applications.

Imagine upgrading a bike from regular tires to high-performance racing tires. The new tires allow the bike to grip better, accelerate faster, and deliver a smoother ride. Similarly, integrating active load components improves the differential amplifier’s performance, enabling it to manage signals more effectively.

--