Explain how transistor works as an Amplifier.

How Transistor Works as an Amplifier

A transistor is a semiconductor device that acts as an electronic switch or amplifier. It is made of three layers of semiconductor material, with a small amount of impurity atoms added to each layer. The three layers are called the emitter, base, and collector.

The Emitter

The emitter is the region of the transistor that emits electrons when it is biased positively relative to the base. The amount of current that flows through the emitter is controlled by the amount of voltage applied between the emitter and the base.

The Base

The base is the region of the transistor that controls the flow of current between the emitter and the collector. The base is very thin, so it can be easily saturated with electrons. Saturation occurs when the base contains so many electrons that it can no longer accept any more.

The Collector

The collector is the region of the transistor that collects the electrons that flow from the emitter. The collector is usually biased negatively relative to the emitter, so the electrons are attracted to it.

Transistor as an Amplifier

When a small signal is applied between the emitter and the base of a transistor, the amount of current that flows through the emitter is increased. This increase in current causes a larger increase in the current that flows through the collector. The ratio of the collector current to the emitter current is called the current gain of the transistor.

The current gain of a transistor is typically very large, so even a small signal applied to the emitter can cause a large signal to be amplified at the collector. This makes transistors ideal for use as amplifiers in electronic circuits.

Biasing

In order for a transistor to operate properly, it must be biased. Biasing involves applying a voltage between the emitter and the base that will cause the transistor to operate in the desired region of its characteristic curve.

There are three main types of biasing:

• Forward-active bias: This is the most common type of biasing. In forward-active bias, the emitter is biased positively relative to the base, and the collector is biased negatively relative to the base. This causes a large increase in the current that flows through the collector when a small signal is applied between the emitter and the base.
• Reverse-active bias: In reverse-active bias, the emitter is biased negatively relative to the base, and the collector is biased positively relative to the base. This causes a small increase in the current that flows through the collector when a small signal is applied between the emitter and the base.
• Saturation: In saturation, the base is saturated with electrons, and the collector current is at its maximum value. Saturation is typically used to turn a transistor on or off.

Transistor Amplifiers

Transistors are used in a variety of amplifier circuits. Some of the most common types of transistor amplifiers include:

• Common-emitter amplifier: This is the most common type of transistor amplifier. In a common-emitter amplifier, the emitter is common to both the input and output signals.
• Common-base amplifier: In a common-base amplifier, the base is common to both the input and output signals.
• Common-collector amplifier: In a common-collector amplifier, the collector is common to both the input and output signals.

Transistors are also used in integrated circuits (ICs). ICs are small electronic devices that contain a large number of transistors and other electronic components. ICs are used in a wide variety of electronic devices, including computers, cell phones, and televisions.