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atlbraves49
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Homework Statement
"What is the physical origin of gain in a BJT?"
I can figure out gain using gain equations but am having a hard time describing the physical origin of gain in a BJT.. can anyone help?
Defennder said:Bear in mind that despite the notion of a "gain" relative to desginated inputs and outputs, conservation of current still holds here. Are you asking how exactly do the semiconductor physics of the BJT cause a "gain" in output?
The physical origin of gain in a BJT (Bipolar Junction Transistor) is the amplification of current due to the flow of majority charge carriers (electrons or holes) from the emitter to the collector, controlled by the minority charge carriers (holes or electrons) in the base region.
A BJT achieves amplification through the process of injecting minority carriers from the base to the collector, which leads to an increase in the majority carrier current from the emitter to the collector. This amplification is controlled by the base current, which acts as a small signal input.
The base region in a BJT serves as a control element for the amplification process. It is very thin and lightly doped, allowing for easy control of the minority carriers and their movement between the emitter and collector regions. The base also acts as a barrier for majority carriers, preventing them from crossing over to the other region.
Current gain in a BJT refers to the amplification of the current flowing through the device, while voltage gain refers to the amplification of the voltage between two terminals. In a BJT, the current gain is typically higher than the voltage gain due to the nature of the device's operation.
The gain in a BJT is affected by factors such as the size and doping levels of the different regions, the material used, the temperature, and the external biasing applied to the device. These factors can impact the flow of majority and minority carriers, leading to changes in the amplification of current and voltage.