A transistor works as an amplifier by taking in a very small weak signal through thebase junction and raising the strength of the weak signal. Explain how a transistorcan do the amplification in common emitter configuration (CE) or common base(CB) configuration with examples.
Question
A transistor works as an amplifier by taking in a very small weak signal through thebase junction and raising the strength of the weak signal. Explain how a transistorcan do the amplification in common emitter configuration (CE) or common base(CB) configuration with examples.
Solution
A transistor can amplify signals in both Common Emitter (CE) and Common Base (CB) configurations. Here's how:
- Common Emitter (CE) Configuration:
In the CE configuration, the emitter is the common terminal to both the input and output, hence the name. The input signal is applied to the base-emitter junction and the output is taken from the collector-emitter junction.
The amplification process in CE configuration can be explained as follows:
- A small change in the base current results in a large change in the collector current. This is because the collector current is β times the base current (Ic = βIb), where β is the current gain of the transistor.
- The output voltage is the product of the collector current and the load resistance (Vout = Ic*Rl). Therefore, a small change in the base current results in a large change in the output voltage, achieving amplification.
For example, if β is 100, a change of 1mA in the base current will result in a change of 100mA in the collector current. If the load resistance is 1kΩ, this will result in a change of 100V in the output voltage.
- Common Base (CB) Configuration:
In the CB configuration, the base is the common terminal to both the input and output. The input signal is applied to the emitter-base junction and the output is taken from the collector-base junction.
The amplification process in CB configuration can be explained as follows:
- A small change in the emitter current results in a similar change in the collector current. This is because the collector current is almost equal to the emitter current (Ic ≈ Ie), as the base current is very small and can be neglected.
- The output voltage is the product of the collector current and the load resistance (Vout = Ic*Rl). Therefore, a small change in the emitter current results in a similar change in the output voltage, achieving amplification.
For example, if the change in the emitter current is 1mA and the load resistance is 1kΩ, this will result in a change of 1V in the output voltage.
In both configurations, the transistor acts as an amplifier by converting a small change in the input current into a large change in the output voltage.
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