A transistor is a semiconductor device that can amplify and switch electronic signals. It consists of three layers of material, typically made of silicon, with two layers doped to create a P-N junction. When a small current is applied to the middle layer, it can control a larger current flowing through the other two layers, thus acting as an amplifier.
Transistors amplify AC signals through a process called "transistor action". When an AC signal is applied to the base of a transistor, it causes the transistor to switch on and off rapidly, thus allowing a larger AC signal to pass through the collector and emitter. This amplification process is achieved through the transistor's ability to control a larger current with a smaller one.
The main difference between a BJT and a MOSFET is their construction and mode of operation. BJTs are made of layers of doped semiconductors and rely on current flow for amplification, while MOSFETs are made of a single layer of semiconductor and use voltage for amplification. MOSFETs also have a higher input impedance and can handle higher power levels than BJTs.
Biasing is the process of supplying DC voltage to a transistor's base terminal to establish a suitable operating point. Proper biasing is necessary for a transistor to amplify AC signals effectively. It ensures that the transistor remains in its active region, where it can provide maximum amplification without distortion.
Transistor amplification is used in a wide range of electronic devices, including radios, televisions, computers, and smartphones. It is also essential in power amplifiers for audio systems, signal processing circuits in communication systems, and control circuits in motor control applications.