27.6. Output Resistance Analysis

While we will be doing this similar kind of exercise, we need to find as I said that we need to find what will be the output resistance R of this voltage amplifier, while we are mapping this small signal equivalent circuit into a voltage amplifier.

This chunk introduces the concept of output resistance in the context of analyzing a voltage amplifier. Output resistance is a crucial parameter because it influences how the amplifier interacts with the load connected to it. When designing amplifiers, it's important to determine this resistance to ensure optimal performance.

Think of output resistance like the size of a pipe carrying water. Just like a larger pipe can carry water more efficiently to its destination, a lower output resistance allows the amplifier to provide a stronger signal to the load, ensuring the message is transmitted clearly.

Again we will be stimulating this circuit from this port by say a signal source called v or say v and then we can observe the corresponding current let we mark it as say i.

This chunk explains the practical approach to measuring output resistance. The circuit is stimulated with a known voltage source, and the corresponding output current is measured. The output resistance can then be calculated by dividing the output voltage by the output current.

Imagine you're using a garden hose. When you open the faucet (apply voltage), water (current) flows out of the hose. By measuring how much water flows out for the pressure you set, you can understand how 'resistive' the hose is, similar to finding output resistance in an electronic circuit.

At the output port what we have it is only R remaining. So, if I am applying v here, the current flow through this circuit it is mainly this is the current.

Here, we focus on the output circuit components. The output resistance primarily consists of a resistor denoted as R. When an input voltage is applied, the current flowing through the circuit is directly related to this resistor, helping us to calculate the output resistance.

Picture a simple electrical circuit as a water tank. The water level (voltage) determines how much water can flow out (current) through the valve (output resistance R). If the valve is narrow (high resistance), less water flows out, and if it's wide (low resistance), more water flows through, much like voltage and current in a circuit.

So, if I consider R also, so R = R ⫽(r + (1+ β) R ).

This equation shows how to calculate total output resistance in a circuit, considering both the internal resistance and others influenced by transistor parameters such as β (beta). It emphasizes that output resistance depends on several factors within the circuit.

Imagine a roadway with multiple lanes. The total traffic flow (current) will depend on how wide each lane (resistance) is. Just as road conditions and lane sizes dictate how smoothly traffic can move, different resistances in a circuit determine how effectively it can deliver power to a load.

This amplifies whatever the voltage gain we see being affected by R E is quite significant, potentially degrading amplification efficiency.

This portion discusses the role of the emitter resistor (R_E) in the circuit. While it serves a stabilizing function, it can reduce voltage gain, which is vital for amplifier performance. This trade-off between stability and gain must be carefully managed in design.

Consider the resistance of a narrow straw when drinking a thick milkshake. The straw stabilizes the milkshake's flow, but it makes it hard to sip. Similarly, an emitter resistor stabilizes the circuit, but at the cost of gain, similar to how a small straw hinders quick sipping.

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