71.2. Discussion on Differential Signals

So, we are discussing about the equivalence of the 2 single ended signal and differential signal pair. Now let me give you some example of that maybe pictorial example of representing individual signal versus common mode and differential part.

In this chunk, the lecture begins by introducing the concept of differential signals in relation to single-ended signals. It clarifies the equivalence between two single-ended signals (where each signal is referenced to a common ground) and the differential signal pair (which represents the difference between these two signals). The lecturer then plans to present visual examples that help differentiate between individual signals as well as their common and differential components.

Consider two friends speaking to each other in a noisy cafe. Their individual voices can be thought of as single-ended signals, while the difference in their voices can be viewed as the differential signal. The background noise represents the common mode, which can distort their conversation if not properly filtered.

Suppose we do have say one signal something like this. See v_{in1} So, we do have one sinusoidal part and on top of that with respect to that we do have seen v_{in1}. So, 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.

In this part, the lecturer describes a graphical example where two sinusoidal waveforms are presented. One wave (pink) represents the actual signal, while the second wave (red) is its complementary signal, which is in the opposite phase. This setup demonstrates how each signal can have distinct roles, with the pink waveform serving as the 'true signal' and the red providing a phase-inverted version of it.

Imagine a seesaw where one side goes up while the other goes down. In this analogy, one side represents the positive phase of the signal, and the other side represents the negative phase. Just as the seesaw reflects the opposing actions of the kids, the signals simulate the opposing values of the waveforms.

If you try to represent say these two signal namely the pink colour and red colour in terms of say differential and the common mode component. So, let me draw the differential part... So this blue signal is v_c.

Here, the lecturer explains how to represent the two signals (the pink and red) in terms of differential and common mode components. The green waveform represents the differential signal derived from the pink and red signals, while the blue waveform represents the average value, also known as the common mode signal, which fluctuates between the two. This introduces the key concepts of differential and common mode signals in relation to their graphical representations.

Think of a choir singing in harmony. The individual voices represent common mode signals (similar tones coming together), while the differences in pitch between the tenors and sopranos create the rich harmonies, which would be the differential signals complementing the overall sound.

So, in case if you want to really find the find out this signal and if you extract this remove the noise part, the blue part then you can take help from this differential amplifier...

This chunk highlights the purpose and importance of differential amplifiers in signal processing. It discusses how a differential amplifier can amplify the true signal (differential component) while suppressing unwanted noise (common mode component). The lecturer emphasizes that for effective noise reduction, a high differential mode gain alongside a low common mode gain is essential.

Imagine you're listening to a friend speak in a crowded room. Using noise-cancelling headphones can be likened to a differential amplifier. They help you focus on your friend's voice (differential signal) and reduce the background chatter (common mode noise), allowing for clearer communication.

Now if I write this equation say this equation what we can say that v = A × v_d.

In this segment, the mathematical model of a differential amplifier is introduced. The output voltage is expressed as the product of the differential gain (A) and the differential input voltage (v_d). This representation allows for practical calculations during amplifier design, ensuring the amplifier operates within the desired parameters.

Think of this equation like a recipe. The amplitude of the output (v) depends on how much 'ingredient' (gain A) you add to the 'mix' (differential input v_d). Depending on how much of each ingredient you use, you can create a tasty dish (desired output), or if too much noise is added, it might not taste as good.

So, the summary is that this is most dangerous thing. So, definitely we want both A_c_d and A should be low.

This chunk wraps up the discussion by underscoring the challenges faced when signals are processed through differential amplifiers. It discusses how unwanted common mode signals can inadvertently be converted into differential signals, complicating the output and underscoring the need to minimize both common mode to differential gain and other non-ideal parameters.

Imagine building a wall to separate your garden from the outside noise. If the wall isn’t strong enough (metaphorically speaking, if you don't minimize those gain parameters), sounds from outside could creep into your garden, disrupting your peaceful atmosphere. This analogy illustrates the importance of maintaining separation between desired and undesired signals.

--