Question

Explain p-n-p transistor as a common emitter amplifier. What are the gains in it?

Hint:

In a common emitter amplifier, the input signal is applied to the base, and the amplified output is taken from the collector. The output is inverted compared to the input.

Answer 1

Step 1: p-n-p Transistor as a Common Emitter Amplifier.
A p-n-p transistor consists of a layer of n-type semiconductor sandwiched between two p-type semiconductors. In a common emitter amplifier configuration, the emitter of the transistor is common to both the input and output. In this configuration: - The input signal is applied to the base of the transistor, and the output is taken from the collector. - The current flowing from the emitter to the collector is amplified by the transistor.
Step 2: Working of Common Emitter Amplifier.
In the common emitter amplifier: - A small input current applied to the base controls a much larger current flowing from the emitter to the collector. - The transistor operates in the active region, where the base-emitter junction is forward biased and the collector-base junction is reverse biased. - The output signal is inverted, meaning that there is a phase shift of 180° between the input and output signals.
Step 3: Gains in the Amplifier.
The two main types of gains in the common emitter amplifier are: 1. **Current Gain**: The current gain \( \beta \) of the transistor is the ratio of the collector current to the base current: \[ \beta = \frac{I_C}{I_B} \] where: - \( I_C \) is the collector current, - \( I_B \) is the base current. 2. **Voltage Gain**: The voltage gain \( A_v \) of the amplifier is the ratio of the change in output voltage to the change in input voltage: \[ A_v = \frac{\Delta V_{\text{out}}}{\Delta V_{\text{in}}} \] The voltage gain depends on the load resistance and the transistor's characteristics.
Step 4: Conclusion.
A p-n-p transistor in a common emitter configuration is widely used for amplification purposes, and its performance is characterized by both current and voltage gains.