When transistor is used as an amplifier, it is biased to work in:

Explanation:

Transistor as an Amplifier

Definition: A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. When used as an amplifier, a transistor takes in a small input signal and produces a larger output signal, effectively increasing the amplitude of the signal.

Working Principle: To function effectively as an amplifier, a transistor must be properly biased, meaning that the voltages at its terminals are set to appropriate levels to ensure it operates in a specific region of its characteristic curves. The region where a transistor is biased to work as an amplifier is the active region.

In the active region, the transistor operates such that the base-emitter junction is forward biased and the collector-base junction is reverse biased. This allows for a controlled flow of electrons from the emitter to the collector, which is modulated by the base current, thereby amplifying the input signal applied at the base.

Advantages of Using Transistor in Active Region:

• High gain: The transistor can provide significant amplification of the input signal.
• Linear operation: The output signal is a linear amplification of the input signal, which is crucial for accurate signal reproduction.
• Stability: The active region ensures stable operation of the transistor as an amplifier.

Disadvantages:

• Power dissipation: Transistors in the active region can dissipate significant power, leading to heating and the need for proper thermal management.
• Limited output swing: The output voltage swing is limited by the supply voltage and the saturation and cutoff regions of the transistor.

Applications: Transistors biased in the active region are widely used in various electronic circuits, including audio amplifiers, radio frequency amplifiers, and other signal processing circuits.

Correct Option Analysis:

The correct option is:

Option 1: Active region

This option correctly describes the region in which a transistor is biased to function as an amplifier. The active region is where the transistor operates linearly, allowing it to amplify the input signal effectively.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Cutoff region

In the cutoff region, the transistor is effectively turned off because the base-emitter junction is not forward biased, and there is no significant current flow from the collector to the emitter. In this region, the transistor cannot amplify signals as it acts as an open switch.

Option 3: Saturation region

In the saturation region, both the base-emitter and base-collector junctions are forward biased, resulting in maximum current flow from the collector to the emitter. In this region, the transistor acts as a closed switch, and it is not suitable for amplification since the output is not a linear function of the input signal.

Option 4: Completely ON state

This option is similar to the saturation region where the transistor is fully turned on, allowing maximum current to flow through it. As with the saturation region, the transistor in this state cannot function as an amplifier due to the lack of linearity in its operation.

Conclusion:

Understanding the operation regions of a transistor is crucial for its application in electronic circuits. For amplification purposes, a transistor must be biased in the active region, where it can provide a linear and stable amplification of the input signal. The active region ensures that the transistor operates correctly as an amplifier, making it essential for various signal processing applications. The other regions, such as cutoff, saturation, and completely ON state, do not support the linear amplification needed for accurate and effective signal amplification.