Field Effect Transistor

A FET’s working principle involves three main components: the source, the drain, and the gate. Its structure typically consists of a semiconductor material with at least three terminals.

FET uses an electric field to regulate current flow between its source and drain terminals based on the voltage applied to its gate terminal. Unlike a bipolar junction transistor, a FET is a voltage-controlled device rather than a current-controlled device. By varying the voltage at the gate terminal, one can modulate or control the current flowing through the channel between the source and drain terminals. This property allows for precise control over the current flow within a circuit and makes the FET useful in various electronic applications such as amplifiers, switches, and oscillators.

Apart from its voltage-controlled nature, a key characteristic of a FET is its high input impedance, which makes it suitable for use in applications where signal amplification and impedance matching are crucial. This high input impedance helps reduce loading effects on preceding stages in a circuit, ensuring signal integrity and fidelity.

Furthermore, FET exhibits low power consumption compared to other transistors, making it an energy-efficient component ideal for portable electronic devices and low-power applications. Its ability to operate at lower power levels without compromising performance makes it highly desirable in modern electronics design.

FETs are of two types – Junction Field Effect Transistor (JFET) and Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET).

1. Junction Field Effect Transistor (JFET)

A JFET is characterized by a junction between the gate and the channel, offering simplicity and robustness. It comes in two forms: n-channel and p-channel. In a n-channel JFET, a negative voltage applied to the gate creates a depletion region, reducing the channel’s conductivity. Conversely, for p-channel JFET, a positive gate voltage enhances the channel’s conductivity by depleting the majority charge carriers.

2. Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET)

MOSFET is prevalent in integrated circuits (ICs) due to its high input impedance and excellent switching characteristics. It features a metal gate insulated by a thin oxide layer from the semiconductor. MOSFET comes in two main varieties: enhancement mode and depletion mode. In enhancement-mode MOSFET, a voltage applied to the gate creates a conducting channel in the semiconductor, enabling current flow. Depletion-mode MOSFETs, conversely, have a conducting channel by default, which diminishes as a voltage is applied to the gate.

One significant difference between a JFET and a MOSFET is their construction and operation principles. While the JFET is a voltage-controlled device that regulates current based on applied voltage, the MOSFET is known for its high input impedance and ability to integrate into digital circuits easily.