Question

What is an essential possible condition of biasing for a transistor to operate in an active region?
A) Forward biasing of emitter base collector base junctions
B) Reverse biasing of emitter-base collector-base junctions C
C) Forward biasing of emitter base & Reverse biasing of collector-base junctions
D) Reverse biasing of emitter-base & Forward biasing of collector-base junctions

Answer 1

Active region in a transistor is the region between cut off and saturation.

If the base-emitter junction is forward biased then the transistor is said to be on. If it is reverse biased, then the transistor is said to be off.

In the active region, collector-base junction remains reverse biased while base-emitter junction remains forward biased.

Step-by-step solution:
Transistor Biasing is the process in which DC operating voltage or current of a transistor is set to a condition to the correct level so that any AC signal fed to the transistor can be amplified correctly by the transistors.

To make the operation of a transistor it is needed to take care of its base current, collector voltage, and collector current values and therefore, if the transistor is to operate correctly as a linear amplifier, it must be properly biased around its operating point.

A transistor has two p-n junctions. So, a transistor is like having two diodes. The junction between base and emitter may be called an emitter diode.
The junction between base and collector may be called collector diode.

A transistor can act in one of the three states:
-Cut-off,
-Saturated and
-Active.
The state of a transistor is completely dependent on the states of the emitter diode and collector diode.

When the transistor is in the active state then collector current is equal to the base current,
${{I}_{C}}~=~{{I}_{B}}$
Therefore, a transistor acts as an amplifier when operating in the active state. Amplification means linear amplification. This is why small signal amplifiers are the most common linear devices.
Hence, forward biasing of emitter base & reverse biasing of collector-base junctions is an essential possible condition of biasing for a transistor to operate in an active region.

Therefore, option C is the correct answer.

Note: The base of the transistor is thinner than the emitter and the collector is wider than both.
The emitter of the transistor is highly doped to inject a large number of charge carriers for current conduction.