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Electronics

Electronics

Electronics is the branch of physics (the science of matter and energy) that deals with the flow of electrons and other carriers of electric charge. This flow of electric charge is known as electric current, and a closed path through which current travels is called an electric circuit.

The modern era of electronics originated in the early twentieth century with the invention of the electron tube. An electron tube is a device that stores electric charges and amplifies (intensifies or strengthens) electronic signals. In 1947 the industry took a giant leap forward when American physicists John Bardeen (19081991), Walter Brattain (19021987), and William Shockley (19101989) developed the smaller, more efficient transistor, which led to a new generation of miniature electronics. In the late 1950s, American physicist Robert Noyce (19271990) invented the silicon integrated circuitan even more efficient way to process electronic impulses that has carried the electronics industry into the computer age. The 1980s saw the development of circuits employing very-largescale integration (VLSI). VLSI technology involves placement of 100,000 or more transistors on a single silicon chip. VLSI greatly expands the computational speed and ability of computers. Microcomputers, medical equipment, video cameras, and communication satellites are just a few examples of devices made possible by integrated circuits. Researchers believe that, in the future, new technologies may make it possible to fit one billion or more transistors on a single chip.

Of the many forms of electronics, none has helped transform our lives more than digital electronics, which began in the 1970s. The personal computer is one of the best examples of this transformation because it has simplified tasks that were difficult or impossible for individuals to complete.

Today electronics has a vast array of applications including television, computers, microwave ovens, radar, radio, sound recording and reproduction equipment, video technology, and X-ray tubes.

[See also Electric current; Transistor; Vacuum tube ]

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electronics

electronics, science and technology based on and concerned with the controlled flow of electrons or other carriers of electric charge, especially in semiconductor devices. It is one of the principal branches of electrical engineering. The invention of the transistor, announced in 1948, and the subsequent development of integrated circuits have brought about revolutionary changes in electronics, which was previously based on the technology of the electron tube. The miniaturization and savings in power brought about by these developments have allowed electronic circuits to be packaged more densely, making possible compact computers, advanced radar and navigation systems, and other devices that use very large numbers of components (see microelectronics). It has also brought to the consumer such items as smaller and more reliable radio and television receivers, advanced sound- and video-recording and reproducing systems, microwave ovens, cellular telephones, and powerful yet inexpensive personal computers. The consumer electronics industry—which began in 1920 when radio broadcasting started in the United States—accounts for annual sales of close to $50 billion in the United States alone. Because of advances in electronics manufacturing technology, the cost of electronic products often decreases even as quality and reliability increase. Power requirements are continually reduced, allowing greater portability.

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Electronics

Electronics

A later development of the work of Albert Abrams (1863-1924) that employs therapeutic apparatus to produce shortwave low-power electromagnetic and alternating magnetic currents to correct disease conditions. Abrams believed that diseases produced peculiar radiations, and that these radiations in turn produce a reflex in living tissue that can be detected by apparatuses and normalized by the appropriate electro-magnetic energy produced by other apparatuses.

In 1922 the College of Electronic Medicine was founded in San Francisco. It was superseded in 1947 by the Electronic Medical Foundation. The magazine Physio-Clinical Medicine, started in 1916, later became the Electronic Medical Digest, reviewing a wide range of developments relating to electromagnetic theories and research in cell radiation and disease therapies.

Sources:

Abrams, Albert. Human Energy. San Francisco: The Author, 1914.

Barr, James. Abrams' Methods of Diagnosis and Treatment. London, 1925.

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electronics

electronics Study and use of circuits based on the conduction of electricity through valves and semiconductors. The diode valve, invented by John Fleming, and the triode valve, invented by Lee De Forest, provided the basic components for all the electronics of radio, television and radar until the end of World War 2. In 1948, a team led by William Shockley produced the first semiconducting transistor. Semiconductor devices do not require the high operating voltages of valves and can be miniaturized as an integrated circuit (IC). This has led to the production of computers and automatic control devices. See also cathode-ray tube; electron; microelectronics; printed circuit; thermionics

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electronics

e·lec·tron·ics / ilekˈträniks; ˌēlek-/ • pl. n. [usu. treated as sing.] the branch of physics and technology concerned with the design of circuits using transistors and microchips, and with the behavior and movement of electrons in a semiconductor, conductor, vacuum, or gas: electronics is seen as a growth industry [as adj.] electronics engineers. ∎  [treated as pl.] circuits or devices using transistors, microchips, and other components.

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Electronics

Electronics

History

Electronic components

Integrated circuits

Resistors, capacitors, and inductors

Sensors

Amplifiers

Oscillators

Power-supply circuits

Microwave electronics

Optical electronics

Digital electronics

Resources

Electronics is a field of engineering and applied physics that grew out of the study and application of electricity. Electricity concerns the generation and transmission of power and uses metal conductors. Electronics manipulates the flow of electrons in a variety of ways and accomplishes this by using gases, semiconducting materials like silicon and germanium, masers, lasers, and microwave tubes. By custom, devices that manipulate the flow of electronics by using only conductors, resistors, and magnetic fields are not considered electronic: a generator or electronic motor is considered an electric machine, not an electronic machine. The distinction is cultural, not fundamental. Electronics applications include radio, radar, television, communications systems and satellites, navigation aids and systems, control systems, space exploration vehicles, watches, many appliances, and computers.

History

The history of electronics is a story of the late nineteenth and early twentieth centuries and of three key componentsthe vacuum tube, the transistor, and the integrated circuit. In 1883, Thomas Alva Edison discovered that electrons flow from one metal conductor to another through a vacuum. This discovery of conduction became known as the Edison effect. In 1904, John Fleming applied the Edison effect in inventing a two-element electron tube called a diode, and Lee De Forest followed in 1906 with the three-element tube, the triode. These vacuum tubes were the devices that made manipulation of electrical energy possible so it could be amplified and transmitted.

The first applications of electron tubes were in radio communications. Guglielmo Marconi pioneered the development of the wireless telegraph in 1896 and long-distance radio communication in 1901. Early radio consisted of either radio telegraphy (the transmission of Morse code signals) or radio telephony (voice messages). Both relied on the triode and made rapid advances thanks to armed forces communications during World War I. Early radio transmitters, telephones, and telegraph used high-voltage sparks to make waves and sound. Vacuum tubes strengthened weak audio signals and allowed these signals to be superimposed on radio waves. In 1918, Edwin Armstrong invented the superheterodyne receiver that could select among radio signals or stations and could receive distant signals. Radio broadcasting grew astronomically in the 1920s as a direct result. Armstrong also invented wide-band frequency modulation (FM) in 1935; only AM or amplitude modulation had been used from 1920 to 1935.

Communications technology was able to make huge advances before World War II as more specialized tubes were made for many applications. Radio as the primary form of education and entertainment was soon challenged by television, which was invented in the 1920s but didnt become widely available until 1947. Bell Laboratories publicly unveiled the television in 1927, and its first forms were electromechanical. When an electronic system was proved superior, Bell Labs engineers introduced the cathode ray picture tube and color television. But Vladimir Zworykin, an engineer with the Radio Corporation of America (RCA), is considered the father of the television because of his inventions, the picture tube and the iconoscope camera tube.

Development of the television as an electronic device benefited from many improvements made to radar during World War II. Radar was the product of studies by a number of scientists in Britain of the reflection of radio waves. An acronym for RA dio D etection A nd R anging, radar measures the distance and direction to an object using echoes of radio microwaves. It is used for aircraft and ship detection, control of weapons firing, navigation, and other forms of surveillance. Circuitry, video, pulse technology, and microwave transmission improved in the wartime effort and were adopted immediately by the television industry. By the mid-1950s, television had surpassed radio for home use and entertainment.

After the war, electron tubes were used to develop the first computers, but they were impractical because of the sizes of the electronic components. In 1947, a team of engineers from Bell Laboratories invented the transistor. John Bardeen, Walter Brattain, and William Shockley received a Nobel Prize for their creation, but few could envision how quickly and dramatically the transistor would change the world. The transistor functions like the vacuum tube, but it is tiny by comparison, weighs less, consumes less power, is much more reliable, and is cheaper to manufacture with its combination of metal contacts and semiconductor materials.

The concept of the integrated circuit was proposed in 1952 by Geoffrey W. A. Dummer, a British electronics expert with the Royal Radar Establishment. Throughout the 1950s, transistors were mass produced on single wafers and cut apart. The total semiconductor circuit was a simple step away from this; it combined transistors and diodes (active devices) and capacitors and resistors (passive devices) on a planar unit or chip. The semiconductor industry and the silicon integrated circuit (SIC) evolved simultaneously at Texas Instruments and Fairchild Semiconductor Company. By 1961, integrated circuits were in full production at a number of firms, and designs of equipment changed rapidly and in several directions to adapt to the technology. Bipolar transistors and digital integrated circuits were made first, but analog ICs, large-scale integration (LSI), and very-large-scale integration (VLSI) followed by the mid-1970s. VLSI consists of thousands of circuits with on-and-off switches or gates between them on a single chip. Microcomputers, medical equipment, video cameras, and communication satellites are only examples of devices made possible by integrated circuits.

Electronic components

Integrated circuits are sets of electronic components that are interconnected. Active components supply energy and include vacuum tubes and transistors. Passive components absorb energy and include resistors, capacitors, and inductors.

Vacuum tubes or electron tubes are glass or ceramic enclosures that contain metal electrodes for producing, controlling, or collecting beams of electrons. A diode has two elements, a cathode and an anode. The application of energy to the cathode frees electrons, which migrate to the anode. Electrons only flow during one half-cycle of an alternating (AC) current. A grid inserted between the cathode and anode can be used to control the flow and amplify it. A small voltage can cause large flows of electrons that can be passed through circuitry at the anode end.

Special purpose tubes use photoelectric emission and secondary emission, as in the television camera tube that emits and then collects and amplifies return beams to provide its output signal. Small amounts of argon, hydrogen, mercury, or neon vapors in the tubes change its current capacity, regulate voltage, or control large currents. The finely focused beam from a cathode-ray tube illuminates the coating on the inside of the television picture tube to reproduce images.

Transistors are made of silicon or germanium containing foreign elements that produce many electrons or few. N-type semiconductors produce a lot of electrons, and p-type semiconductors do not. Combining the materials creates a diode, and when energy is applied, the flow can be directed or stopped depending on direction. A triple layer with either n-p-n or p-n-p creates a triode, which, again can be used to amplify signals. The field-effect transistor or FET superimposes an electric field and uses that field to attract or repel charges. The field can amplify the current much like the grid does in the vacuum tube. FETs are very efficient because only a small field controls a large signal. A controlling terminal or gate is called a JFET or junction FET. Addition of metal semiconductors, metal oxides, or insulated gates produce other varieties of transistor that enhance different signal-transmitting aspects.

Integrated circuits

An integrated circuit consists of tens of thousands of transistors and other circuit elements that are fabricated in a substrate of inert material. That material can be ceramic or glass for a film-integrated circuit or silicon or gallium-arsenide for a semiconductor integrated circuit (SIC). These circuits are small pieces or chips that may be 0.080.15 sq in long (24 sq mm long). Designers are able to place these thousands of components on a chip by using photolithography to place the components and minute conducting paths in the proper patterns for the purpose of each type of circuit. Many chips are made simultaneously on a 4-sq-in (10-sq-cm) wafer.

Several methods are used to introduce impurities into the silicon in the planar process. A mask with some regions isolated is placed over the surface or plane of the wafer, and the surface of the silicon is altered or treated to modify its electrical character. Crystals of silicon are grown on the substrate in a process called epitaxy; another method, thermal oxidation, grows a film of silicon dioxide on the surface that acts as a gate insulator. During solid-state diffusion, impurities diffused as a gas or spread in a beam of ions are distributed or redistributed in regions of the semiconductor. The number of impurities diffused into the crystal can be carefully controlled so the movement of electrons through the chip will also be specific. Coatings can also be added by chemical vapor deposition, evaporation, and a method called sputtering used to deposit tungsten on the substrate; the results of all these methods are coatings on the substrate or disturbed surfaces of the substrate that are only atoms thick. Etching and other forms of lithography (using electron beams or x rays) are also used to pattern the wafer surface for the interconnection of the surface elements.

Resistors, capacitors, and inductors

Resistance to the flow of current can be controlled by the conductivity of the material, dimensions over which current flows, and the applied voltage. In electronic circuits, metal films, mixtures containing carbon, and resistance wire are used to make resistors. Capacitors have the ability to retain charge and voltage and to act as conductors, especially when currents change in flow. Inductors regulate rapid changes in signals and current intensity.

Sensors

Sensors are specialized electronic devices that detect changes in quantities such as temperature, electrical power levels, chemical concentrations, physical position, fluid flow, or mechanical properties like velocity or acceleration. When a sensor responds to change, it usually requires a transducer to convert the quantity the sensor has measured into electrical signals that are translated into printouts, electronic readouts, recordings, or information that is returned to the device to control the change measured. Specialized resistors and capacitors are sometimes used as combined sensors and transducers. Variable resistors respond to mechanical motions by changing them to electrical signals. The thermistor varies its resistance with temperature; a thermocouple also measures temperature changes in the form of small voltages as temperatures are measured at two different junctions on the thermocouple. Usually, sensors produce weak electronic signals, and added circuits amplify these. But sensors can be operated from a distance and in conditions such as extreme heat or cold or contaminated environments where working conditions are unpleasant or hazardous to humans.

Amplifiers

Amplifiers are electronic devices that boost current, voltage, or power. Amplifiers are classed according to what sort of signal they amplify: audio amplifiers, for example, which increase the power of signals that can (when transduced into sound waves) be heard by the human ear, are used in radios, televisions, cassette recorders, sound systems, and citizens band radios. They receive sound as electrical signals, amplify these, and convert them to sound in speakers. Video amplifiers increase the strength of the visual information seen on the television screen by regulating the brightness of the image-forming light. Radio frequency amplifiers are used to amplify the signals of communication systems for radio or television broadcasting and operate in the frequency range from 100 kHz to 1 GHz and sometimes into the microwave-frequency range. Video amplifiers increase all frequencies equally up to 6 MHz; audio amplifiers, in contrast, usually operate below 20 kHz. But both audio and video amplifiers are linear amplifiers that proportion the output signal to the input received; that is, they do not distort signals. Other forms of amplifiers are nonlinear and do distort signals usually to some cutoff level. Nonlinear amplifiers boost electronic signals for modulators, mixers, oscillators, and other electronic instruments.

Oscillators

Oscillators are amplifiers that receive an incoming signal and their own output as feedback (that is, also as input). They produce radio and audio signals for precision signaling, such as warning systems, telephone electronics between individual telephones and central telephone stations, computers, alarm clocks, high-frequency communications equipment, and the high-frequency transmissions of broadcasting stations.

Power-supply circuits

Electronic equipment usually operates on direct current (DC) power supplies because these are more easily regulated. Power supplies in electrical outlets, however, are alternating currents (AC), so electronic equipment must be able to convert AC to DC. A team of devices is used for this conversion. The piece of equipment has an internal transformer that adjusts the voltage it receives from the outlet up or down to suit operation of the equipment. The transformer is also a ground, a type of insulation that reduces the possibility of electrical shock. A rectifier converts AC to DC, and a capacitor filters the converted voltage to level out any fluctuations. A voltage regulator may take the place of the capacitor, especially in more sophisticated equipment; modern voltage regulators are manufactured as integrated circuits.

Microwave electronics

Microwaves are the frequencies of choice for many forms of communications especially telephone and television signals that are transmitted long distances through overland methods, broadcast stations, and satellites. Microwave electronics are also used for radar.

Microwaves are within the frequency of 3 GHz to about 300 GHz; because of their high frequency spectrum, microwaves can carry large numbers of channels. They also have short wavelengths from 10 cm to 0.1 cm; wavelength dictates the size of antenna that can be used to transmit that particular wavelength, so the small antennae for microwave communications are very practical. They do require repeater stations to make long-distance links.

Electronic devices like capacitors, inductors, oscillators, and amplifiers were not usable with microwaves because their high frequency and the speeds of electrons are not compatible. This complication of component size was studied in detail in the 1930s. Finally, it was found that the velocity of the electrons could be modulated to the advantage of microwave applications. The modulating device, the klystron, was a tube that amplified the microwave signal in a resonating cavity. The klystron could amplify only a narrow range of microwave frequencies, but the traveling-wire tube (invented in 1934)a similar velocity modulatorcould amplify a wider frequency band using a wire helix instead of a resonating cavity.

High-powered and high-pulsed microwave use especially for radar required another device, the magnetron. The magnetron was perfected in 1939 and was a tube with multiple resonating cavities. While these devices were successful for their specialized uses, they were expensive and bulky (like other vacuum tubes); they have been replaced completely by semiconductors and integrated circuits with equally sophisticated and specialized solutions for handling the high frequencies of microwaves that fit much smaller spaces and can be mass produced economically.

Microwave electronics have also required adaptations of other parts of transmission systems. Conventional wires cannot carry microwaves because of the energy they give off; instead, coaxial cables can carry microwaves up to 5 GHz in frequency because their self-shielding conductors prevent radiating energy. Waveguides are used for higher-frequency microwave transmission; waveguides are hollow metal tubes with a refractive interface that reflects energy back. Microstrips are an alternative to waveguides that connect microwave components and work by separating two conductors with dielectric material. Microstrips (also called striplines) can be manufactured using integrated circuit (IC) technology and are compatible with the small size of ICs.

Masers were first developed in 1954. The Maser (M icrowave A mplification by S timulated E mission of R adiation) can be used for amplifying and oscillating microwaves in signals from satellites, atomic clocks, spacecraft, and radio. Masers focus molecules in an excited energy state into a resonant microwave cavity which then emits them as stimulated emission of radiation through the microwave output.

Optical electronics

Optical electronics involve combined applications of optical (light) signals and electronic signals. Opto-electronics have a number of uses, but the three general classifications of these uses are to detect light, to convert solar energy to electric energy, and to convert electric energy to light. Like radio waves and microwaves, light is also a form of electromagnetic radiation except that its wavelength is very short. Photodetectors allow light to irradiate a semiconductor that absorbs the light as photons and converts these to electric signals. Light meters, burglar alarms, and many industrial uses feature photodetectors.

Solar cells convert light from the sun to electric energy. They use single-crystal doped silicon to reduce internal resistance and metal contacts to convert over 14% of the solar energy that strikes their surfaces to electrical output voltage. Cheaper, polycrystalline silicon sheets and other lenses are being developed to reduce the cost and improve the effectiveness of solar cells.

Light-emitting diodes (LEDs) direct incoming voltage to gallium-arsenide semiconductors that, when agitated, emit photons of light. The wavelength of the emitted light depends on the material used to construct the semiconductor. The LED is used in many applications where illuminated displays are needed on instruments and household appliances. Liquid crystal displays (LCDs) use very low power levels to produce reflected or scattered light; they cannot be seen in the dark like LED displays because they do not produce light. Conductive patterns of electrodes overlie parallel-plate capacitors that hold large molecules of the liquid crystal material that works as the dielectric.

Like microwaves, optical electronics use waveguides to reflect, confine, and direct light. The most familiar form of optical waveguide is the optic fiber.

These fine, highly specialized glass fibers are made of silica that has been doped with germanium dioxide.

Digital electronics

Digital electronics are the electronics that transformed our lives beginning in the 1970s. The personal computer is one of the best examples of this transformation because it has simplified tasks that were difficult or impossible for individuals to accomplish. Digital devices use simple true-false or on-off statements to represent information and to make decisions. In contrast, analog devices use a continuous system of values. Because digital devices only recognize one of two permissible signals, they are more tolerant to noise (unwanted electronic signals) and a range of components than analog devices. Digital systems are built of a collection of components that process, store, and transmit or communicate information. The basis of these components is the logic circuit that makes the true-false decision from what may be many true-false signals. The logic circuit is an integrated circuit from any one of a number of families of digital logic devices that use switches, transducers, and timing circuits to function. Digital logic gates are the most elementary inputs and outputs in a logic device. A logic gate is based on a simple operation in Boolean algebra (a form of mathematics that uses logic variables to express thought processes). For example, a logic gate may perform an or, and, or not function; to make it capable of a nor function, an or gate is followed by an inverter. By linking combinations of these gates, any decision is possible.

The most common form of logic circuit is probably the transistor-wtransistor logic (TTL) circuit. High-speed systems use emitter-coupled logic (ELC), and the complementary metal oxide semiconductor (CMOS) logic uses lower speeds to also lower power levels. Logic gates are also combined to make static-memory cells. These are combined in a rectangular array to form the random-access memory (RAM) familiar to home computer users. The binary digits that make up this memory are called bits, and typical large-scale integrated (LSI) circuit memory chips have over 16, 000 bits of static memory. Dynamic memory cells use capacitors to send memory to a selected cell or to write to that cell. Very-large-scale chips with 256, 000 bits per chip were made beginning in the 1980s, and dynamic memory made these possible because of its high density. By 2006, microprocessor chips with many millions of transistors were commonplace: the Intel Core Duo, used in many Macintosh computers from 2006 onward, contained 151 million transistors. Also by 2006, RAM chips

KEY TERMS

Epitax The growth of a crystalline substance on a substrate such that the crystals imitate the orientation of those in the substrate.

storing 1 gigabyte (billion bytes, 8 billion bits) had become commonplace.

Microprocessors have replaced combinations of switching and timing circuits. They are programmed to perform sets of tasks and a wider variety of logic functions. Electronic games and digital watches are examples of microprocessor systems. Digital methods have revolutionized music, library storage, medical electronics, and television, among thousands of other tools that influence our lives daily. Future developments in computer architecture are directed toward greater speed and more memory capacity. In most forms of electronics, increased miniaturization permits increased complexity at fixed or decreasing cost. This trend, driven by strong market forces, is sure to continue for many years to come.

Resources

BOOKS

Gates, Earl. Introduction to Electronics. Clifton Park, NY: Thomson Delmar Learning, 2006.

Gibilisco, Stan. Teach Yourself Electricity and Electronics. 4th ed. New York: McGraw-Hil, 2006.

Mathews, Thomas W. Introduction to Electronics. Indianapolis, IN: Addison-Wesley, 2005.

Pooranchandra S., et al. Introduction To Electrical, Electronics, and Communications Engineering. New Delhi, India: Laxmi Publications, 2005.

Gillian S. Holmes

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Electronics

Electronics

Electronics is a field of engineering and applied physics that grew out of the study and application of electricity . Electricity concerns the generation and transmission of power and uses metal conductors. Electronics manipulates the flow of electrons in a variety of ways and accomplishes this by using gases, materials like silicon and germanium that are semiconductors, and other devices like solar cells, light-emitting diodes (LEDs), masers, lasers, and microwave tubes. Electronics applications include radio , radar , television , communications systems and satellites, navigation aids and systems, control systems, space exploration vehicles, microdevices like watches, many appliances, and computers.


History

The history of electronics is a story of the twentieth century and three key components—the vacuum tube , the transistor , and the integrated circuit . In 1883, Thomas Alva Edison discovered that electrons will flow from one metal conductor to another through a vacuum . This discovery of conduction became known as the Edison effect. In 1904, John Fleming applied the Edison effect in inventing a two-element electron tube called a diode , and Lee De Forest followed in 1906 with the three-element tube, the triode. These vacuum tubes were the devices that made manipulation of electrical energy possible so it could be amplified and transmitted.

The first applications of electron tubes were in radio communications. Guglielmo Marconi pioneered the development of the wireless telegraph in 1896 and long-distance radio communication in 1901. Early radio consisted of either radio telegraphy (the transmission of Morse code signals) or radio telephony (voice messages). Both relied on the triode and made rapid advances thanks to armed forces communications during World War I. Early radio transmitters, telephones, and telegraph used high-voltage sparks to make waves and sound. Vacuum tubes strengthened weak audio signals and allowed these signals to be superimposed on radio waves . In 1918, Edwin Armstrong invented the "super-heterodyne receiver" that could select among radio signals or stations and could receive distant signals. Radio broadcasting grew astronomically in the 1920s as a direct result. Armstrong also invented wide-band frequency modulation (FM) in 1935; only AM or amplitude modulation had been used from 1920 to 1935.

Communications technology was able to make huge advances before World War II as more specialized tubes were made for many applications. Radio as the primary form of education and entertainment was soon challenged by television, which was invented in the 1920s but didn't become widely available until 1947. Bell Laboratories publicly unveiled the television in 1927, and its first forms were electromechanical. When an electronic system was proved superior, Bell Labs engineers introduced the cathode ray picture tube and color television. But Vladimir Zworykin, an engineer with the Radio Corporation of America (RCA), is considered the "father of the television" because of his inventions, the picture tube and the iconoscope camera tube.

Development of the television as an electronic device benefitted from many improvements made to radar during World War II. Radar was the product of studies by a number of scientists in Britain of the reflection of radio waves. An acronym for RAdio Detection And Ranging, radar measures the distance and direction to an object using echoes of radio microwaves. It is used for aircraft and ship detection, control of weapons firing, navigation, and other forms of surveillance. Circuitry, video, pulse technology, and microwave transmission improved in the wartime effort and were adopted immediately by the television industry. By the mid-1950s, television had surpassed radio for home use and entertainment.

After the war, electron tubes were used to develop the first computers, but they were impractical because of the sizes of the electronic components. In 1947, the transistor was invented by a team of engineers from Bell Laboratories. John Bardeen, Walter Brattain, and William Shockley received a Nobel prize for their creation, but few could envision how quickly and dramatically the transistor would change the world. The transistor functions like the vacuum tube, but it is tiny by comparison, weighs less, consumes less power, is much more reliable, and is cheaper to manufacture with its combination of metal contacts and semiconductor materials.

The concept of the integrated circuit was proposed in 1952 by Geoffrey W. A. Dummer, a British electronics expert with the Royal Radar Establishment. Throughout the 1950s, transistors were mass produced on single wafers and cut apart. The total semiconductor circuit was a simple step away from this; it combined transistors and diodes (active devices) and capacitors and resistors (passive devices) on a planar unit or chip. The semiconductor industry and the silicon integrated circuit (SIC) evolved simultaneously at Texas Instruments and Fairchild Semiconductor Company. By 1961, integrated circuits were in full production at a number of firms, and designs of equipment changed rapidly and in several directions to adapt to the technology. Bipolar transistors and digital integrated circuits were made first, but analog ICs, large-scale integration (LSI), and very-large-scale integration (VLSI) followed by the mid-1970s. VLSI consists of thousands of circuits with on-and-off switches or gates between them on a single chip. Microcomputers, medical equipment, video cameras, and communication satellites are only examples of devices made possible by integrated circuits.


Electronic components

Integrated circuits are sets of electronic components that are interconnected. Active components supply energy and include vacuum tubes and transistors. Passive components absorb energy and include resistors, capacitors, and inductors.

Vacuum tubes or electron tubes are glass or ceramic enclosures that contain metal electrodes for producing, controlling, or collecting beams of electrons. A diode has two elements, a cathode and an anode . The application of energy to the cathode frees electrons which migrate to the anode. Electrons only flow during one half-cycle of an alternating (AC) current. A grid inserted between the cathode and anode can be used to control the flow and amplify it. A small voltage can cause large flows of electrons that can be passed through circuitry at the anode end.

Special purpose tubes use photoelectric emission and secondary emission, as in the television camera tube that emits and then collects and amplifies return beams to provide its output signal. Small amounts of argon, hydrogen , mercury, or neon vapors in the tubes change its current capacity, regulate voltage, or control large currents. The finely focused beam from a cathode-ray tube illuminates the coating on the inside of the television picture tube to reproduce images.

Transistors are made of silicon or germanium containing foreign elements that produce many electrons or few. N-type semiconductors produce a lot of electrons, and p-type semiconductors do not. Combining the materials creates a diode, and when energy is applied, the flow can be directed or stopped depending on direction. A triple layer with either n-p-n or p-n-p creates a triode, which, again can be used to amplify signals. The field-effect transistor or FET superimposes an electric field and uses that field to attract or repel charges. The field can amplify the current much like the grid does in the vacuum tube. FETs are very efficient because only a small field controls a large signal. A controlling terminal or gate is called a JFET or junction FET. Addition of metal semiconductors, metal oxides, or insulated gates produce other varieties of transistor that enhance different signal-transmitting aspects.

Integrated circuits

An integrated circuit consists of tens of thousands of transistors and other circuit elements that are fabricated in a substrate of inert material. That material can be ceramic or glass for a film-integrated circuit or silicon or gallium-arsenide for a semiconductor integrated circuit (SIC). These circuits are small pieces or chips that may be 0.08–0.15 sq in long (2–4 sq mm long). Designers are able to place these thousands of components on a chip by using photolithography to place the components and minute conducting paths in the proper patterns for the purpose of each type of circuit. Many chips are made simultaneously on a 4-sq-in (10-sq-cm) wafer.

Several methods are used to introduce impurities into the silicon in the planar process. A mask with some regions isolated is placed over the surface or plane of the wafer, and the surface of the silicon is altered or treated to modify its electrical character. Crystals of silicon are grown on the substrate in a process called epitaxy; another method, thermal oxidation, grows a film of silicon dioxide on the surface that acts as a gate insulator. During solid-state diffusion , impurities diffused as a gas or spread in a beam of ions are distributed or redistributed in regions of the semiconductor. The number of impurities diffused into the crystal can be carefully controlled so the movement of electrons through the chip will also be specific. Coatings can also be added by chemical vapor deposition, evaporation , and a method called sputtering used to deposit tungsten on the substrate; the results of all these methods are coatings on the substrate or disturbed surfaces of the substrate that are only atoms thick. Etching and other forms of lithography (using electron beams or x rays ) are also used to pattern the wafer surface for the interconnection of the surface elements.


Resistors, capacitors, and inductors

Resistance to the flow of current can be controlled by the conductivity of the material, dimensions over which current flows, and the applied voltage. In electronic circuits, metal films, mixtures containing carbon , and resistance wire are used to make resistors. Capacitors have the ability to retain charge and voltage and to act as conductors, especially when currents change in flow. Inductors regulate rapid changes in signals and current intensity.


Sensors

Sensors are specialized electronic devices that detect changes in quantities such as temperature , electrical power levels, chemical concentrations, physical position, fluid flow, or mechanical properties like velocity or acceleration . When a sensor responds to change, it usually requires a transducer to convert the quantity the sensor has measured into electrical signals that are translated into printouts, electronic readouts, recordings, or information that is returned to the device to control the change measured. Specialized resistors and capacitors are sometimes used as combined sensors and transducers. Variable resistors respond to mechanical motions by changing them to electrical signals. The thermistor varies its resistance with temperature; a thermocouple also measures temperature changes in the form of small voltages as temperatures are measured at two different junctions on the thermocouple. Usually, sensors produce weak electronic signals, and added circuits amplify these. But sensors can be operated from a distance and in conditions such as extreme heat or cold or contaminated environments where working conditions are unpleasant or hazardous to humans.


Amplifiers

Amplifiers are electronic devices that boost current, voltage, or power. Audio amplifiers are used in radios, televisions, cassette recorders, sound systems, and citizens band radios. They receive sound as electrical signals, amplify these, and convert them to sound in speakers. Video amplifiers increase the strength of the visual information seen on the television screen by regulating the brightness of the image-forming light . Radio frequency amplifiers are used to amplify the signals of communication systems for radio or television broadcasting and operate in the frequency range from 100 kHz to 1 GHz and sometimes into the microwave-frequency range. Video amplifiers increase all frequencies equally up to 6 MHz; audio amplifiers, in contrast, usually operate below 20 kHz. But both audio and video amplifiers are linear amplifiers that proportion the output signal to the input received; that is, they do not distort signals. Other forms of amplifiers are nonlinear and do distort signals usually to some cutoff level. Nonlinear amplifiers boost electronic signals for modulators, mixers, oscillators, and other electronic instruments.


Oscillators

Oscillators are amplifiers that receive an incoming signal and their own output as feedback (that is, also as input). They produce radio and audio signals for precision signaling, such as warning systems, telephone electronics between individual telephones and central telephone stations, computers, alarm clocks, high-frequency communications equipment, and the high-frequency transmissions of broadcasting stations.

Power-supply circuits

Electronic equipment usually operates on direct current (DC) power supplies because these are more easily regulated. Power supplies in electrical outlets, however, are alternating currents (AC), so electronic equipment must be able to convert AC to DC. A team of devices is used for this conversion. The piece of equipment has an internal transformer that adjusts the voltage it receives from the outlet up or down to suit operation of the equipment. The transformer is also a ground, a type of insulation that reduces the possibility of electrical shock. A rectifier converts AC to DC, and a capacitor filters the converted voltage to level out any fluctuations. A voltage regulator may take the place of the capacitor, especially in more sophisticated equipment; modern voltage regulators are manufactured as integrated circuits.


Microwave electronics

Microwaves are the frequencies of choice for many forms of communications especially telephone and television signals that are transmitted long distances through overland methods, broadcast stations, and satellites. Microwave electronics are also used for radar.

Microwaves are within the frequency of 3 GHz to about 300 GHz; because of their high frequency spectrum , microwaves can carry large numbers of channels. They also have short wavelengths from 10 cm to 0.1 cm; wavelength dictates the size of antenna that can be used to transmit that particular wavelength, so the small antennae for microwave communications are very practical. They do require repeater stations to make long-distance links.

Electronic devices like capacitors, inductors, oscillators, and amplifiers were not usable with microwaves because their high frequency and the speeds of electrons are not compatible. This complication of component size was studied in detail in the 1930s. Finally, it was found that the velocity of the electrons could be modulated to the advantage of microwave applications. The modulating device, the klystron, was a tube that amplified the microwave signal in a resonating cavity. The klystron could amplify only a narrow range of microwave frequencies, but the traveling-wire tube (invented in 1934)—a similar velocity modulator—could amplify a wider frequency band using a wire helix instead of a resonating cavity.

High-powered and high-pulsed microwave use especially for radar required another device, the magnetron. The magnetron was perfected in 1939 and was a tube with multiple resonating cavities. While these devices were successful for their specialized uses, they were expensive and bulky (like other vacuum tubes); they have been replaced completely by semiconductors and integrated circuits with equally sophisticated and specialized solutions for handling the high frequencies of microwaves that fit much smaller spaces and can be mass produced economically.

Microwave electronics have also required adaptations of other parts of transmission systems. Conventional wires can not carry microwaves because of the energy they give off; instead, coaxial cables can carry microwaves up to 5 GHz in frequency because their self-shielding conductors prevent radiating energy. Waveguides are used for higher-frequency microwave transmission; waveguides are hollow metal tubes with a refractive interface that reflects energy back. Microstrips are an alternative to waveguides that connect microwave components and work by separating two conductors with dielectric material. Microstrips (also called striplines) can be manufactured using integrated circuit (IC) technology and are compatible with the small size of ICs.

Masers were first developed in 1954. The Maser (Microwave Amplification by Stimulated Emission of Radiation) can be used for amplifying and oscillating microwaves in signals from satellites, atomic clocks, spacecraft, and radio. Masers focus molecules in an excited energy state into a resonant microwave cavity which then emits them as stimulated emission of radiation through the microwave output.


Optical electronics

Optical electronics involve combined applications of optical (light) signals and electronic signals. Optoelectronics have a number of uses, but the three general classifications of these uses are to detect light, to convert solar energy to electric energy, and to convert electric energy to light. Like radio waves and microwaves, light is also a form of electromagnetic radiation except that its wavelength is very short. Photodetectors allow light to irradiate a semiconductor that absorbs the light as photons and converts these to electric signals. Light meters, burglar alarms, and many industrial uses feature photodetectors.

Solar cells convert light from the sun to electric energy. They use single-crystal doped silicon to reduce internal resistance and metal contacts to convert over 14% of the solar energy that strikes their surfaces to electrical output voltage. Cheaper, polycrystalline silicon sheets and other lenses are being developed to reduce the cost and improve the effectiveness of solar cells.

Light-emitting diodes (LEDs) direct incoming voltage to gallium-arsenide semiconductors that, when agitated, emit photons of light. The wavelength of the emitted light depends on the material used to construct the semiconductor. The LED is used in many applications where illuminated displays are needed on instruments and household appliances. Liquid crystal displays (LCDs) use very low power levels to produce reflected or scattered light; they cannot be seen in the dark like LED displays because they do not produce light. Conductive patterns of electrodes overlie parallel-plate capacitors that hold large molecules of the liquid crystal material that works as the dielectric.

Like microwaves, optical electronics use waveguides to reflect, confine, and direct light. The most familiar form of optical waveguide is the optic fiber. These fine, highly specialized glass fibers are made of silica that has been doped with germanium dioxide.


Digital electronics

Digital electronics are the electronics that transformed our lives beginning in the 1970s. The personal computer is one of the best examples of this transformation because it has simplified tasks that were difficult or impossible for individuals to accomplish. Digital devices use simple "true-false" or "on-off" statements to represent information and to make decisions. In contrast, analog devices use a continuous system of values. Because digital devices only recognize one of two permissible signals, they are more tolerant to noise (unwanted electronic signals) and a range of components than analog devices. Digital systems are built of a collection of components that process, store, and transmit or communicate information. The basis of these components is the logic circuit that makes the true-false decision from what may be many true-false signals. The logic circuit is an integrated circuit from any one of a number of families of digital logic devices that use switches, transducers, and timing circuits to function. Digital logic gates are the most elementary inputs and outputs in a logic device. A logic gate is based on a simple operation in Boolean algebra (a form of mathematics that uses logic variables to express thought processes). For example, a logic gate may perform an "or," "and," or "not" function; to make it capable of a "nor" function, an "or" gate is followed by an inverter. By linking combinations of these gates, any decision is possible.

The most popular form of logic circuit is probably the transistor-transistor logic (TTL) circuit. High-speed systems use emitter coupled logic (ELC), and the complementary metal oxide semiconductor (CMOS) logic uses lower speeds to also lower power levels. Logic gates are also combined to make static-memory cells. These are combined in a rectangular array to form the random-access memory (RAM) familiar to home computer users. The binary digits that make up this memory are called "bits," and typical large-scale integrated (LSI) circuit memory chips have over 16,000 bits of static memory. Dynamic memory cells use capacitors to send memory to a selected cell or to "write" to that cell. Very-large-scale chips with 256,000 bits per chip were made beginning in the 1980s, and dynamic memory made these possible because of its high density .

Microprocessors have replaced combinations of switching and timing circuits. They are programmed to perform sets of tasks and a wider variety of logic functions. Electronic games and digital watches are examples of microprocessor systems. Digital methods have revolutionized music, library storage, medical electronics, and high definition television, among thousands of other tools that influence our lives daily. Future changes to socalled "computer architecture" are directed at greater speed; ultra-high-speed computers may operate by using superconducting circuits that operate at extremely cold temperatures, and integrated circuits that house hundreds of thousands of electronic components on one chip may be commonplace on our desktops.


Resources

books

Boylstad, Robert, and Louis Nashalsky. Electronics: A Survey. Englewood Cliffs, NJ: Prentice Hall, 1985.

Houglum, Roger J. Electronics: Concepts, Applications andHistory. 2nd ed. Albany, NY: Delmar Publishers, 1985.

Patrick, Dale R., and Stephen W. Fardo. Understanding Electricity and Electronics. Upper Saddle River, NJ: Prentice Hall, 1989.

Riordan, Michael, and Lillian Hoddeson. Crystal Fire: TheBirth of the Information Age. New York: W. W. Norton & Company, 1997.

Vergarra, William C. Electronics in Everyday Life. New York: Dover Publications, Inc., 1984.

periodicals

Adler, Jerry. "Three Magic Wands." Newsweek (Winter 1997): 6+.

Bains, Sunny. "Double Helix Doubles as Engineer." Science (March 27, 1998): 2043+.

"Elephant Chips." Discover (July 1998): 62.


Gillian S. Holmes

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Epitaxy

—The growth of a crystalline substance on a substrate such that the crystals imitate the orientation of those in the substrate.

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