Wirral & District Amateur Radio Club



A semiconductor is a crystalline material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber). It has intermediate values of electrical resistivity (its electrical conductivity at room temperature is between that of a conductor and that of an insulator). At high temperatures its conductivity approaches that of a metal and at low temperatures it acts as an insulator. The most common semiconductor materials are silicon and germanium. Silicon is by far the more widely used semiconductor for electronics, partly because it can be used at much higher temperatures than germanium. These materials can either be used in their pure “intrinsic” forms or can be doped to create an excess or lack of electrons. Doping involves adding elements into a semiconductor material during the manufacturing process to increase its conductivity. The impurities added are called dopants. Common dopants include arsenic, antimony, bismuth and phosphorous. The type and level of doping determines whether the semiconductor is N-type (negative), where the current is conducted by excess free electrons or P-type (positive), where the current is conducted by electron vacancies. A semiconductor device is any of a wide variety of devices that employ the electrical properties of semiconductor materials to control the flow of electrons. Such devices include diodes, transistors, logic devices, integrated circuits, voltage regulators, operational amplifiers, etc

A diode is a two-terminal electronic device containing an anode and a cathode, that permits current flow predominantly in only one direction. It has a low resistance to electric current in one direction and a high resistance to it in the reverse direction. This property makes a diode useful as a rectifier, which can convert alternating current (AC) into direct current (DC). When the voltage applied in the reverse direction exceeds a certain value, a semiconductor diode “breaks down” and conducts heavily in the direction of normally high resistance. When the reverse voltage at which breakdown occurs remains nearly constant for a wide range of currents, the phenomenon is called avalanching. A diode using this property is called a Zener diode. It can be used to regulate the voltage in a circuit. Semiconductor diodes can be designed to have a variety of characteristics. Light-sensitive or photosensitive diodes can be used to measure illumination; the voltage drop across them depends on the amount of light that strikes them. A light-emitting diode (LED) produces light as current passes through it.

A logic circuit is an electric circuit whose output depends upon the input in a way that can be expressed as a function in symbolic logic; it has one or more binary inputs (capable of assuming either of two states, e.g., “on” or “off”) and a single binary output. Logic circuits that perform particular functions are called gates.

Basic logic circuits include the AND gate, the OR gate, and the NOT gate, which perform the logical functions AND, OR, and NOT. Logic circuits can be built from any binary electric or electronic devices, including switches, relays, electron tubes, solid-state diodes, and transistors; the choice depends upon the application and design requirements.

A transistor is an active semiconductor device, which possesses at least three terminals (typically, a base, emitter, and collector). A small current in the centre or base region can be used to control a larger current flowing between the end regions (emitter and collector). It is characterised by its ability to amplify current and is used in a wide variety of equipment such as amplifiers, oscillators and switching circuits. (It is a shortened form of transfer resistor.)

An electronic circuit built on a semiconductor substrate, usually one of single-crystal silicon. The circuit, often called a chip, is packaged in a hermetically sealed case or a non-hermetic plastic capsule, with leads extending from it for input, output, and power-supply connections and for other connections that may be necessary when the device is put to use. Integrated circuits can be classified into two groups based on the type of transistors they contain. Bipolar integrated circuits contain bipolar junction transistors as their principle elements. Metal-oxide-semiconductor (MOS) integrated contain MOS transistors as their principle elements. Some integrated circuits contain both types of transistors. Integrated circuits are also categorised according to the number of transistors or other active circuit devices they contain. An IC is said to use small-scale integration (SSI) if it contains fewer than 10 transistors. An IC that contains from 10 to 100 transistors is said to use medium-scale integration. A large-scale integration (LSI) IC contains from 100 to 1,000 transistors, and one that uses very-large-scale integration (VLSI) contains more than 1,000 transistors. Some integrated circuits are analogue devices; an operational amplifier is an example. Other ICs, such as the microprocessors used in computers, are digital devices. Some hybrid integrated circuits contain both analogy and digital circuitry; a bilateral switch, which switches analogy signals by means of a digital control signal is an example of a hybrid IC. Integrated circuit functions are virtually limitless. Improvements in IC manufacturing have led to increasingly dense and capable integrated circuits.

A circuit or device that produces a nearly constant voltage output, even though the voltage input (line) and current output (load) vary widely.

An amplifier characterised by very high gain and input impedance, and very low output impedance. The output voltage is proportional to its input voltage with gain

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