50.1. Analog Electronic Circuits

Yeah. So, welcome back after the short break. So, we are talking about the biasing of Common Gate and Common Base circuits. Now we are going to discuss about the small signal analysis.

In this section, the lecturer introduces the topic of common base and common gate amplifiers. After a brief break, they shift focus towards understanding the biasing of these circuits and the analysis of their small signal behavior. Biasing is crucial because it establishes the operating point of the amplifier, ensuring it functions correctly in response to input signals.

Think of biasing like setting the thermostat in your house. Just as you set a specific temperature for comfort, in amplifiers, biasing sets the optimal operating point to ensure that the amplifier amplifies signals effectively.

So, let me go to the corresponding circuit here yeah. So, we do have common base circuit here. So, this is the common base amplifier and this is the corresponding small signal equivalent circuit. For to save some time what I have done is that I have drawn this circuit, but I will explain that what the things I have done are.

The lecturer presents a common base amplifier and its small signal equivalent circuit. The small signal analysis is important to simplify and analyze how the amplifier behaves with small input signals. Key components such as resistors and voltage sources are highlighted with assumptions made regarding DC currents and grounding.

Imagine translating a complex recipe into simple steps. The small signal equivalent circuit simplifies the workings of the common base amplifier into more manageable parts, just like breaking down a recipe into ingredients and actions.

We say v is essentially 0 ‒ v. So, we can say that v is ‒ v.

This chunk discusses the voltage relationships within the common base amplifier's small signal equivalent circuit. The note v (base node) is considered grounded, simplifying calculations in analyzing how input and output relate. This step is crucial in deriving the voltage gain of the amplifier.

It's similar to keeping one end of a rope fixed on the ground; as you tug the other end (input), the effect on the fixed point (output) becomes much clearer, allowing for easier calculations of force or tension changes.

We do have three current elements. One is one current is flowing through this r another current is flowing through on this device...

In this section, the application of Kirchhoff's Current Law (KCL) at the collector node is discussed, which helps to express currents in terms of voltages. By analyzing the current flowing through different components, the lecturer derives an equation that relates the input and output voltages.

Imagine a busy intersection where vehicles (currents) flow in and out. By observing how many cars enter and exit, you can infer traffic patterns and estimate the traffic flow, much like how KCL helps understand current directions in a circuit.

We can write the expression of v in terms of v. So, with the rearrangement property...

The voltage gain of the amplifier is derived from the previously established equations. The lecturer emphasizes the relationship between input and output voltages and discusses how this relates to different configurations like the common emitter amplifier. An important aspect highlighted is the phase difference between input and output signals.

Consider a sound amplification system in a concert. The input sound (v) is amplified (vout) but often, the amplified sound has to go through a series of adjustments before you hear it, similar to how voltage gain adjusts and phases can change in circuits.

If we consider source resistance signal source resistance and if we look into the input resistance of this circuit...

The section introduces input impedance analysis, highlighting how the source resistance affects the overall voltage gain of the circuit. It's crucial here to note that the small input resistance can significantly influence the amplitude of the signal reaching the transistor.

Think of a water hose: if the hose is narrow (low input resistance), it might limit the water (signal) flowing to the garden plants (transistor), even if the original water flow (source signal) is quite strong.

Now let me consider the common gate configuration...

The lecturer transitions to discussing the common gate configuration for amplifiers, providing a framework analogous to the common base amplifier but with distinct structural differences. The focus shifts to input and output configurations and how the small signal equivalent analysis can align with this configuration.

Consider different doors leading into a building. Each door allows entry but might direct you differently inside. Just as each amplifier configuration channels signals uniquely, the common gate impacts how inputs and outputs are handled.

Now, if I consider common gate: so, common gate circuit configuration...

Input resistance for the common gate configuration is analyzed similarly to the previous configurations. The derived expression shows how input resistance can affect circuit performance, echoing the previous discussions on common base amplifiers.

This is akin to how different types of microphones capture sound. Some might have higher resistance to ambient noise (low input resistance) while others don't, which can significantly affect audio clarity.

So, this is coming . So, there will be huge you know attenuation depending on the condition...

The final chunks summarize the implications of finite input resistance and how it affects overall gain—particularly noting that higher source resistance can lead to attenuation, which weakens the desired signal.

Imagine trying to listen to your favorite song at a loud party. If someone turns on a loudspeaker (high source resistance), your ability to hear the song (signal) diminishes—a metaphor for signal attenuation in electronic circuits.

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