23.8.1. Four Basic Amplifier Types

Welcome back after the short break. So, before the break we are talking about the Model of Voltage Amplifier. And, as I have given a hint that the amplifier need not be always voltage amplifier.

In this introduction, the speaker makes it clear that while voltage amplifiers are commonly discussed, they are not the only type of amplifier. Amplifiers can vary based on the relationship between the input and output signals.

Think of amplifiers like different types of vehicles: just as some are designed for speed (like sports cars), others are designed for carrying heavy loads (like trucks). Likewise, amplifiers are designed to handle different types of signals, not just voltage.

So, let us talk about other kinds of amplifier called current amplifier. And, whenever we are talking about current amplifier similar to voltage amplifier, what does it mean is that, it is an equivalent linear circuit, which provides dependency of the output signal output current signal on the input current signal.

Current amplifiers specifically focus on amplifying current signals rather than voltage. This means that the output current changes based on the input current, establishing a direct relationship between the two.

Imagine you are in a conversation, and you are encouraged to talk more (increase your 'current'). A friend listens closely and responds (the 'output current'), showing how your words affect their engagement.

At the base of the transistor what you can say that the base current to the transistor it is having two components. Namely the I , the DC part, and also the time varying part which is shown here.

In a current amplifier, the input signal to the transistor consists of two parts: a direct current (DC) component and an alternating (varying) part. This allows the amplifier to manage both stable and varying signals.

Think of a musical performance: the base current is like the consistent beat (DC component), while the varying part (AC component) is the melody that changes and flows throughout the song.

And hence we need to put one DC blocking capacitor or it is referred as AC coupling capacitor. So, for time varying signal, whether it is current or voltage whatever you say, that we can think of this capacitor is essentially working as a shot.

An AC coupling capacitor prevents DC signals from affecting the output, allowing only the time-varying part of the signal to pass through. This is essential for accurately amplifying signals that vary over time without getting distorted by constant offsets.

Imagine a filter that only lets certain sounds through, like a music filter that allows only the melody (changing sounds) while blocking the noise from background traffic (DC signals).

Whenever we are talking about the model of the current amplifier, similar to voltage amplifier. What we are looking for it is simplified equivalent circuit, which must represent this entire circuit, in terms of finding the relationship between this final output to this input.

Developing a model for the current amplifier requires simplifying the circuit to find how the input current affects the output current. This model helps in understanding the essential relationships between the inputs and outputs.

A simplified map can help you navigate through a city. In the same way, a circuit model simplifies complex relationships to show how changes in input affect output, making it easier to understand.

The moment we connect to load at the output instead of directly shorting. So, if I am having a finite resistance at the output so, it is expected that the practically the current flowing through the circuit may not be same as the internal current.

When a load is added to the output, it affects the available current due to resistance. The effective current seen will differ from the internal current, primarily due to additional resistances introduced by the load.

If you were pouring a drink into a cup and suddenly added a lid, the flow of liquid (current) would change. Similarly, adding a load changes how current behaves in a circuit.

So, if you look into say this input port the i it is as I said that it will be. So, we can write in that i equals to. So, whatever the i we do have multiplied by this parallel resistance in.

The current amplifier model consists of parameters that capture how input and output currents interact, particularly how they respond to various resistances at both input and output ports.

Consider the water flow in a garden hose: the amount of water (current) that reaches the end depends not only on the faucet's flow (input current) but also on any kinks or resistance in the hose (input and output resistances).

--