Which of the following statements correctly describes the static characteristics of transistors in common emit

Question

Which of the following statements correctly describes the static characteristics of transistors in common emitter configuration?

Examoogle · Accepted Answer

The correct answer is Option A: between the input and output voltage.. In a Common Emitter (CE) amplifier configuration, there is a phase shift of $180^\circ$ (or $\pi$ radians) between the input and output voltage signals. This occurs because the transistor acts as an inverting amplifier; as the base current increases, the collector current increases, causing a greater voltage drop across the collector load resistor, which results in a decrease in the collector-emitter voltage.

Step-by-Step Solution & Concepts:
In a Common Emitter (CE) amplifier configuration, there is a phase shift of $180^\circ$ (or $\pi$ radians) between the input and output voltage signals. This occurs because the transistor acts as an inverting amplifier; as the base current increases, the collector current increases, causing a greater voltage drop across the collector load resistor, which results in a decrease in the collector-emitter voltage.

Working Principle: In the CE configuration, the input signal is applied at the base-emitter junction and the output is taken from the collector-emitter junction. When the input signal goes positive, the base current increases, leading to a larger collector current ($I_C = \beta I_B$). This causes the voltage drop across the collector resistance ($V_C = V_{CC} - I_C R_C$) to increase, resulting in a decrease in the output voltage, thereby creating the $180^\circ$ phase inversion.

Key Formulas: $V_{out} = -\beta R_C I_{in}$ — represents the phase-inverted relationship where $\beta$ is the current gain; $\Delta V_{out} = -A_v \Delta V_{in}$ — where $A_v$ is the voltage gain and the negative sign indicates $180^\circ$ phase shift

Key Points: Common Emitter configuration provides both voltage and current gain.; The output voltage is $180^\circ$ out of phase with the input.; It is the most widely used transistor configuration for amplification.; The phase shift occurs due to the common emitter acting as an inverting terminal.

Advantages: High voltage gain; High current gain; Moderate input and output impedance

Disadvantages: Signal inversion is not always desired in specific circuits; High-frequency performance is limited by the Miller effect

Applications: Audio frequency amplifiers; Voltage amplifiers in radio receivers

Additional Info: The phase shift of $180^\circ$ is a characteristic property of the common emitter amplifier.. Option D is incorrect because the CE configuration does not maintain phase alignment; it inverts the signal.

Answer: A is correct — There is a $180^\circ$ phase shift between the input and output voltage in a common emitter transistor configuration.

Exam Tip: Always remember that only the Common Emitter (CE) configuration provides signal inversion ($180^\circ$ phase shift); Common Base (CB) and Common Collector (CC) configurations do not invert the signal.

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Option B: between the input and output voltage.

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Option C: between the input and output voltage.

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Option D: There is no phase shift between the input and output voltage.

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