71.2.3. Amplification Overview

So, we do have one sinusoidal part and on top of that with respect to that we do have seen v_in1. So, we may say that this pink colour is v_in1 and then if I consider say v_in2. So, that is also with respect to this dotted blue line and that is also sinusoidal, but it is in opposite phase. So, the pink one you may say it is true signal and the red one it is the complimentary signal and inside that whatever you see this is the signal and difference of these two it is basically the differential v_in_d.

In this section, we define the concepts of differential and common mode signals. A differential signal is the difference between two individual signals, while a common mode signal is the average of those two signals. For instance, imagine two sound waves, one from a singer (true signal) and another from a background noise (complimentary signal). The overall sound heard is a combination of both, but by focusing on the difference (differential signal), we can enhance the singer's voice while reducing the noise.

Think of it like listening to music in a noisy café. The singer's voice is the true signal (v_in1) and the café noise is the opposite signal (v_in2). When you want to hear the singer better, you focus on the difference in volume between the singer's voice and the background noise.

So, if I say that it is a differential mode gain a_d it is said high. So, if this is say high quote and unquote high and the common mode gain a_c if I say it is having low value then at the output whatever the v_o_d you will get.

This section emphasizes the importance of having a high differential mode gain (a_d) and a low common mode gain (a_c). A high a_d means that the differential signal is amplified significantly compared to any noise present in the input. In contrast, a low a_c means that the unwanted background noise has minimal impact on the output. Essentially, we want our differential amplifier to focus on the desired signal while disregarding disturbances.

Consider a radio tuned to a specific station. If the station strength (differential mode gain) is strong, you hear the music clearly. However, if the static (common mode signal) is faint, it won't disrupt your listening experience. The clearer the music, the better the radio is at filtering out noise.

Say for example, if I am having say amplitude of say this signal it is say 1. So, which means that peak to peak it is say 2 V, whereas, a the blue one that you consider blue one it is having large amplitude say 8 V. So, naturally if I try to amplify this signal both v_in1 and v_in2 by single ended amplifier then I cannot remove this component.

This segment discusses the output from a differential amplifier when dealing with both desired and unwanted components. For example, if the desired signal has an amplitude of 1V (peak-to-peak 2V) but the noise signal has an amplitude of 8V, using a single-ended amplifier would make it difficult to filter out the noise during amplification. Hence, a differential amplifier is necessary to effectively isolate and amplify the desired signal while minimizing the noise impact.

Imagine you're speaking on a phone call in a crowded train station. If the person on the other end is trying to hear you (the desired signal) but the noise from the crowd is much louder, they will struggle to catch what you're saying. However, if you use a directional microphone (like a differential amplifier), it amplifies your voice while reducing the crowd noise, making it easier for the other person to understand you.

So, intuitively at least you understand that why these 2 parameters are important for this differential amplifier. In fact, they are the vital parameters of characterizing the differential amplifier.

Here, the discussion summarizes the significance of differential and common mode gains in characterizing the performance of differential amplifiers. High a_d and low a_c are essential for the effective functioning of these amplifiers, ensuring they can effectively separate useful signals from noise.

Think about a well-functioning coach at a sports event. A great coach (high a_d) is able to build strategies that enhance their team's performance while ignoring distractions like the crowd's noise (low a_c). This allows the team to focus better and perform optimally.

Now if I write this equation say this equation what we can say that v_o_d = A_d × v_in_d. So likewise if I see this equation, we can see that v_o_c = A_c × v_in_c which means that if the circuit it is linearized and if I stimulate the circuit only with this part keeping this = 0 then at the output we will be getting only v_d.

This section introduces the equations that describe the output of a differential amplifier. The output voltages for the differential signal (v_o_d) and common mode signal (v_o_c) can be expressed in terms of their respective gains. It emphasizes that during linear operation, if only the differential signal is stimulated while keeping the common mode input zero, the output will clearly represent only the differential signal.

Imagine a clear glass window (the differential amplifier) that only allows light from a specific angle (the differential signal) to pass through. If you change angles slightly and add an obstruction (the common mode signal), the glass still focuses on the clear light while minimizing the impact of any obstructions. This is what happens in a differential amplifier under ideal conditions.

--