Which of the following options for the output characteristics of a common-base (CB) configuration of BJT is INCORRECT?

Explanation:

A common-base (CB) configuration of a Bipolar Junction Transistor (BJT) is one of the three basic transistor configurations, where the base terminal is common to both the input and output circuits. It is often used in high-frequency applications due to its low input impedance and high output impedance.

Output Characteristics: The output characteristics of a CB configuration are typically plotted between the output current (collector current, I_C) and the output voltage (voltage across the collector and base terminals, V_CB) for different levels of input current (emitter current, I_E). These characteristics provide important insights into the transistor's behavior and operational regions.

Characteristics:

• The graph typically consists of three regions: the cutoff region, the active region, and the saturation region.
• In the active region, I_C remains approximately constant for a given I_E, even as V_CB increases. This is because the transistor is operating as an amplifier in this region.
• However, due to the Early effect, there is a slight increase in I_C with increasing V_CB, as the effective base width decreases, leading to a higher collector current.

Correct Option Analysis:

The correct option is:

Option 3: In a CB configuration, the current gain is slightly greater than one.

This option is incorrect. In a common-base configuration, the current gain (denoted as α) is defined as the ratio of the collector current (I_C) to the emitter current (I_E). Since a small portion of the emitter current is lost as base current (I_B), the current gain is always slightly less than 1. Mathematically: α = IC / IE, where α < 1.

Typical values of α range from 0.95 to 0.99 for most BJTs, depending on their design and manufacturing process. Therefore, the statement that the current gain is slightly greater than one is factually incorrect