EASA Module 4 key terms

A material whose electrical conductivity lies between that of a conductor and an insulator, and which can be controlled by doping, temperature, or applied voltage. Silicon and germanium are common examples used in electronic devices.

The deliberate addition of small amounts of impurity atoms to a pure semiconductor to increase its free-carrier concentration. Donor impurities create n-type material; acceptor impurities create p-type material.

The boundary formed when p-type and n-type semiconductor materials are joined in one crystal. It allows current mainly in one direction and is the basis of diodes and transistors.

A thin zone at a PN junction where mobile charge carriers have diffused away, leaving fixed ionised atoms. It acts as a barrier to current flow and widens under reverse bias.

Applying a voltage that makes the p-side of a PN junction positive relative to the n-side. This narrows the depletion region and allows conventional current to flow easily through the diode.

Applying a voltage that makes the p-side negative relative to the n-side. This widens the depletion region and blocks normal current, leaving only a tiny leakage current.

A two-terminal semiconductor device that conducts current mainly from anode to cathode. It converts alternating current into pulsating direct current in power-supply circuits.

A diode designed to operate safely in reverse breakdown at a specified voltage. It maintains a nearly constant voltage and is used for voltage regulation and reference purposes.

A semiconductor diode that emits light when forward biased, as electrons recombine with holes. Colour depends on the semiconductor material and its bandgap energy.

A diode operated in reverse bias whose leakage current increases with incident light. It converts optical signals into electrical current in sensors and receivers.

A three-terminal semiconductor device with emitter, base, and collector, made of two PN junctions. A small base current controls a larger collector current, allowing amplification or switching.

A field-effect transistor with a metal-oxide-semiconductor gate insulated from the channel. Voltage on the gate controls conduction between source and drain, giving high input resistance and efficient switching.

A four-layer semiconductor device that latches into conduction when a gate pulse is applied, then remains on until current falls below a holding level. It is used for power control.

A complete electronic circuit fabricated on a single small piece of semiconductor, called a chip. It contains many transistors, diodes, and resistors interconnected to perform a specific function.

An insulating board with patterned copper conductors that mechanically supports and electrically connects electronic components. It replaces point-to-point wiring and gives repeatable, compact circuits.

The insulating base material of a printed circuit board that provides mechanical strength and electrical isolation between conductors. Common types include woven glass reinforced epoxy and polyimide.

A widely used flame-retardant printed circuit board substrate made of woven glass cloth bonded with epoxy resin. It offers good mechanical strength and electrical insulation at moderate cost.

A narrow strip of copper etched on a printed circuit board that carries electrical current between pads and components. Its width and thickness determine current capacity and resistance.

A small area of exposed copper on a printed circuit board where a component lead or solder joint is attached. Pads anchor components and connect them to traces.

A small plated hole in a printed circuit board that electrically connects copper layers. It allows signals and power to pass between the top, inner, and bottom layers.

A hole drilled through a printed circuit board and plated with copper so that a component lead can be soldered and connected to conductors on different layers.

A method of mounting components directly onto the surface of a printed circuit board using solder paste and reflow, instead of inserting leads through holes.

A thin protective polymer layer applied over a printed circuit board, leaving only pads and test points exposed. It prevents solder bridges and protects copper from oxidation.

The printed legend on a circuit board showing component outlines, reference designators, and orientation marks. It helps assemblers and technicians place and identify parts.

A large continuous area of copper on a printed circuit board connected to the circuit's zero-volt reference. It lowers impedance, reduces noise, and provides a return path for currents.

A printed circuit board with three or more copper layers separated by insulating material and joined by plated vias. It allows dense routing, power planes, and controlled impedance.

A closed-loop control system that uses feedback to make a mechanical output follow a commanded position, speed, or other variable. It automatically corrects errors between command and actual output.

The process of taking part of the output signal and returning it to the input for comparison with the command. Negative feedback reduces error and improves accuracy and stability.

A control arrangement in which the output is measured and compared continuously with the desired input, and the difference drives the system to reduce error.

The difference between the commanded input and the measured feedback in a servomechanism. It is amplified to drive the motor or actuator until the error becomes zero.

A motor designed for precise control of position, speed, or torque in a feedback system. It responds quickly to command changes and often includes low-inertia rotors and position sensors.

A small generator driven by a servo shaft that produces a voltage proportional to speed. Its output provides velocity feedback for damping and speed regulation.

An electromechanical sensor with rotor and stator windings that outputs voltages representing shaft angle. It provides accurate position feedback and is robust in harsh environments.

A rotary transformer-like device whose windings produce voltages that indicate shaft position. Synchros are used in pairs or chains to transmit angular data in control systems.

An electronic power amplifier that takes a low-level error signal and supplies the current and voltage needed to drive a servo motor. It may also shape the response for stability.

A small range of input change to which a servomechanism does not respond, often caused by friction or backlash. It produces a steady-state position error.

Lost motion between meshing gears or mechanical parts when direction reverses. In a servo system it causes delay and position error, reducing accuracy.

The reduction of unwanted oscillation in a servo system, usually by feeding back a signal proportional to velocity. Adequate damping gives a quick response without excessive overshoot.

The amount by which a servo output passes beyond its commanded value before settling. Excessive overshoot indicates poor damping and can cause instability.

The ability of a servomechanism to settle at its commanded value without continuous or growing oscillation after a disturbance or command change.