Question:medium
When an n-p-n junction transistor is used as an amplifier in common emitter mode,
When an n-p-n junction transistor is used as an amplifier in common emitter mode,
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In CE mode, the input is small (Base), output is big (Collector), and the signal is "flipped" ($180^\circ$ shift).
Updated On: May 14, 2026
- the base emitter junction is reverse biased.
- the input impedance is high and the output impedance is low.
- input signal is applied between the base and emitter and the output is obtained between collector and emitter.
- the input voltage and the output voltage are in phase.
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
A Bipolar Junction Transistor (BJT) can be configured in three modes: Common Base (CB), Common Emitter (CE), and Common Collector (CC).
The CE configuration is the most widely used for amplification because it provides both good voltage gain and current gain.
Step 2: Detailed Explanation:
Let's analyze the properties of a CE amplifier to evaluate the options:
- Biasing for Active Region: For a transistor to work as an amplifier, it must operate in the active region. This requires the Base-Emitter (BE) junction to be {forward biased} and the Base-Collector (BC) junction to be {reverse biased}. Thus, option (A) is incorrect.
- Impedances: A CE amplifier typically has a moderate input impedance (due to forward-biased BE junction) and a moderately high output impedance (due to reverse-biased BC junction). The property of "high input and low output impedance" is characteristic of the Common Collector (emitter follower) configuration. Thus, option (B) is incorrect.
- Connections: "Common Emitter" means the emitter terminal is common to both the input and output circuits. Therefore, the input signal is applied across the Base and Emitter, and the amplified output is taken across the Collector and Emitter. This precisely matches option (C).
- Phase Relationship: In a CE amplifier, the output voltage is $180^\circ$ out of phase with the input voltage (it acts as an inverter). Thus, option (D) is incorrect.
Step 4: Final Answer:
The correct statement is that the input signal is applied between the base and emitter and the output is obtained between collector and emitter.
A Bipolar Junction Transistor (BJT) can be configured in three modes: Common Base (CB), Common Emitter (CE), and Common Collector (CC).
The CE configuration is the most widely used for amplification because it provides both good voltage gain and current gain.
Step 2: Detailed Explanation:
Let's analyze the properties of a CE amplifier to evaluate the options:
- Biasing for Active Region: For a transistor to work as an amplifier, it must operate in the active region. This requires the Base-Emitter (BE) junction to be {forward biased} and the Base-Collector (BC) junction to be {reverse biased}. Thus, option (A) is incorrect.
- Impedances: A CE amplifier typically has a moderate input impedance (due to forward-biased BE junction) and a moderately high output impedance (due to reverse-biased BC junction). The property of "high input and low output impedance" is characteristic of the Common Collector (emitter follower) configuration. Thus, option (B) is incorrect.
- Connections: "Common Emitter" means the emitter terminal is common to both the input and output circuits. Therefore, the input signal is applied across the Base and Emitter, and the amplified output is taken across the Collector and Emitter. This precisely matches option (C).
- Phase Relationship: In a CE amplifier, the output voltage is $180^\circ$ out of phase with the input voltage (it acts as an inverter). Thus, option (D) is incorrect.
Step 4: Final Answer:
The correct statement is that the input signal is applied between the base and emitter and the output is obtained between collector and emitter.
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