Function and Purpose of MOSFETs

Understanding MOSFETs

MOSFET stands for METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR.
It’s a type of transistor, a device used to amplify or switch electronic signals in a circuit.
The MOSFET is one of the most integral components in analogue circuits, due to its high input impedance and fast switching speed.

A MOSFET has four parts: the source, the drain, the gate and the substrate or body.
The source and drain are two terminals that are made up of ‘doped’ semiconductor, meaning it contains extra impurity atoms to produce extra charge carriers.
A voltage applied to the gate controls the current flowing from the source to the drain.
The gate is separated from the body by an insulating layer, typically made of silicon dioxide or a similar insulator. That’s why MOSFETs are voltage-controlled devices, as opposed to BJTs (bipolar junction transistors) that are current-controlled.

MOSFETs are mostly used in circuits as electronic switches or amplifiers, relying on the ability to control the voltage and consequently the conductivity between the drain and source.
They are often used in applications such as power amplifiers, motor drives, and voltage level translators.
In an amplifier circuit, the MOSFET can provide signal gain as it controls the output signal based on the input signal with a high degree of precision.

There are two main types of MOSFETs: N-channel and P-channel, or NMOS and PMOS.
NMOS turn on (conduct) when the gate voltage is higher than the source voltage.
PMOS, on the other hand, turns on when the gate voltage is lower than the source voltage.
Each of these types has its uses in different electronic configurations and they are typically chosen based on the specific requirements of the circuit.

In all, the MOSFET is key in controlling circuits in analogue systems, making it an invaluable component in a variety of electronic devices.