Transistors

Transistors are semiconductor devices that amplify or switch electronic signals and electrical power. They control the flow of current or voltage through a circuit by using a small input signal to modulate a larger output signal. Transistors are the fundamental building blocks of modern electronic devices, enabling complex circuits such as amplifiers, memory, and microprocessors.

Two main families: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs use current at the input (base current) to control a larger current between collector and emitter, and come in NPN and PNP polarities. FETs control current by voltage applied to a gate, with MOSFETs and JFETs as examples. The MOSFET is the most widely used transistor type in digital integrated circuits.

Operation: In a BJT, a small base current modulates the charge carrier flow across a junction, providing current gain. In a MOSFET, a voltage on the gate modulates the conductivity of a channel between source and drain, resulting in high input impedance.

Materials: most transistors use silicon, sometimes germanium or compound semiconductors. Silicon's native oxide enables reliable insulation for MOS devices.

History: The transistor was invented in 1947 at Bell Labs by John Bardeen, Walter Brattain, and William Shockley, revolutionizing electronics and enabling integrated circuits developed in the following decades.

Applications: amplification, switching in power electronics, radio frequency circuits, digital logic, microprocessors, memory elements.

Characteristics: key parameters include current gain (beta for BJTs), transconductance, threshold voltage, on-resistance, gain-bandwidth product, and packaging. They have finite temperature sensitivity and switching speeds that influence circuit design.