Which of the following statements is FALSE for a common-base (CB) amplifier using a BJT?

Explanation:

In the analysis of a common-base (CB) amplifier using a Bipolar Junction Transistor (BJT), it is crucial to understand the fundamental properties and characteristics that define its operation and performance. Here we will delve into the properties of a CB amplifier and identify which statement is false among the given options.

Common-Base (CB) Amplifier Characteristics:

A common-base amplifier configuration is one where the base of the transistor is common to both the input and output circuits. This means the input is applied to the emitter and the output is taken from the collector, with the base typically grounded or at a fixed bias voltage.

Here are some key characteristics of a CB amplifier:

• Input Impedance: The input impedance of a CB amplifier is generally very low because the input is applied at the emitter, which presents a low impedance path.
• Output Impedance: The output impedance is typically high because the output is taken from the collector, which has a high impedance path.
• Voltage Gain: The voltage gain of a CB amplifier can be significant because it is proportional to the load resistance divided by the input resistance.
• Current Gain: The current gain is less than unity (typically it is close to one but slightly less), making it a current buffer.
• Frequency Response: CB amplifiers have a wide frequency response, making them suitable for high-frequency applications.

Analysis of the Given Statements:

Let's analyze each statement in the context of the characteristics of a CB amplifier:

This statement is true. As mentioned earlier, the input impedance of a CB amplifier is low because the emitter presents a low impedance path, and the output impedance is high because the collector presents a high impedance path.

This statement is true. The output characteristics of a CB amplifier are typically represented by a plot of the output current (IC) versus the output voltage (VCB), showing how the output current varies with the output voltage for different levels of input current.

This statement is false. The output impedance of a CB amplifier is higher than that of a common-emitter amplifier. In a common-emitter configuration, the output impedance is lower due to the feedback effect of the emitter resistor, whereas in a CB configuration, there is no such feedback effect, resulting in higher output impedance.

This statement is true. The input characteristics of a CB amplifier are typically represented by a plot of the input current (IE) versus the input voltage (VEB), showing how the input current varies with the input voltage for different levels of output voltage.

1. It has lower input impedance and higher output impedance.
2. The output characteristics is a plot of output current (IC) vs. output voltage (VCB).
3. The output impedance is lower than that of a common-emitter amplifier.
4. The input characteristics is a plot of input current (IE) vs. input voltage (VEB).

Based on the analysis, the correct answer is option 3: "The output impedance is lower than that of a common-emitter amplifier." This statement is false because, in reality, the output impedance of a CB amplifier is higher than that of a common-emitter amplifier.

Important Information:

Understanding the differences between various transistor amplifier configurations (such as common-base, common-emitter, and common-collector) is essential for designing and analyzing electronic circuits. Each configuration has its unique characteristics and applications:

• Common-Emitter (CE) Amplifier: Known for its high voltage gain and moderate input and output impedances. It is widely used in amplifier circuits for its good overall performance.
• Common-Collector (CC) Amplifier: Also known as an emitter follower, it has a high input impedance, low output impedance, and a voltage gain of approximately unity. It is commonly used for impedance matching and buffering applications.
• Common-Base (CB) Amplifier: Characterized by low input impedance, high output impedance, and wide frequency response. It is suitable for high-frequency applications and situations where impedance matching is required.

By understanding these configurations and their properties, engineers can select the appropriate amplifier type for their specific application, ensuring optimal performance and efficiency in electronic circuits.