Basic to Advanced Electronics

Electronics is part of the broad field of electricity.  Electricity includes two important elements: (1) electric current and (2) electric voltage.  Electric current is the flow of electric charges.  Electric voltage is a type of "pressure" or force that causes the charges to move in the same direction.  Familiar uses of electricity include the furnishing of energy in homes and businesses to provide light and heat, and to drive motors.

Electronics deals chiefly with the use of current and voltage to carry electric signals.  An electric signal is an electric current or voltage modified in some way to represent information.  A signal may represent sound, pictures, numbers, letters, computer instructions, or other information.  Signals can also be used to count objects, to measure time or temperature, or to detect chemicals or radioactive materials.

Electronics depends on certain highly specialized components, such as transistors and integrated circuits, that serve as part of almost all electronic equipment.  The value of such devices lies in their ability to manipulate signals extremely fast.  Some components can respond to signals billions of times per second.

The field of microelectronics is concerned with the design and production of miniature components, chiefly integrated circuits, and of electronic equipment that uses such components.  Manufacturers can create millions of microscopic electronic components on a piece of material--called a chip--that is no larger than a fingernail.

This article provides a broad overview of the basic tools and functions of electronics and the electronics industry.  Separate Information Finder articles give detailed information on many of the topics.  For a list of these articles, see the Related Articles at the end of this article.

Uses of Electronics

Electronics has changed the way people live.  People have come to depend on electronic products in almost every part of their daily lives.

In Communications.  Electronic communication systems link people throughout the world.  Radio can transmit a voice around the world in a fraction of a second.  People in different countries communicate almost instantly through telephones and computers.  A television viewer can watch events on another continent as they are taking place.  Cellular telephones enable a person to call another person while riding in a car or walking down the street.  Fax machines send and receive copies of documents over telephone lines in minutes.

Processing Information.  Electronic computers are used in business, schools, government, industry, scientific laboratories, and the home.  People depend on computers to handle vast amounts of information with incredible speed and to solve complex mathematical problems in a fraction of a second.  On-line services provide computer users instant access to a wide variety of information and features through telephone lines.

Medicine and Research.  Physicians use a variety of electronic instruments and machines to diagnose and treat disorders.  For example, X-ray machines use radiation produced in a special type of electronic vacuum tube to take pictures of bones and internal organs.  Physicians analyze these pictures to detect injuries and diseases.  Radiation therapy, or radiotherapy, uses X rays and other forms of radiation as a powerful weapon against cancer.  Many hearing-impaired people depend on electronic hearing aids to amplify (strengthen) sound waves.

Computers and other electronic instruments provide scientists and other researchers with a clearer understanding of nature.  For example, computers help scientists design new drug molecules, track weather systems, and test theories that describe how galaxies develop.  Electron microscopes can magnify specimens by 1 million times.

Automation.  Electronic controls improve the operation of many common home appliances, such as refrigerators, sewing machines, toasters, and washing machines.  People can program coffeemakers, lawn sprinklers, and many other products to turn on and off automatically.  Electronic devices control video games.  Microwave ovens heat food quickly by penetrating it with short radio waves produced by a vacuum tube.

Industries use computers to control other machines.  Electronic robots perform a wide variety of tasks that are boring, difficult, or dangerous for people.  For example, some automobiles are painted by robots using spray paint that would harm people who breathed it.

Air, sea, and space travel depend on navigation by radar, radio, and computers.  Many automobiles have electronic controls in their engines and fuel systems.  Also, electronic devices control the inflation of air bags, safety devices that inflate to protect a driver or a front-seat passenger in a head-on collision.

How an Electronic System Works

To provide a basis for understanding electronics, this section describes how a common product, a handheld electronic calculator, works.  A calculator has a small keypad with keys for numbers and operations, and a display screen that shows results.  Most calculators are powered by a small battery or by a panel of solar cells.

Beneath the keypad, tiny circuits operate the calculator.  A circuit is a set of connected parts through which current flows.  Pressing a key creates a pulse of electric charge representing a number or operation--in other words, a signal.  The signals travel through wires to the circuits.

Each circuit has a job.  Some circuits store signals temporarily, awaiting further instructions.  Others change signals according to instructions.  For example, a circuit might multiply two numbers together.  Finally, circuits send signals that light up or darken certain areas on the display screen to show the result of a calculation.

The operations of a calculator, like most electronic systems, can be divided into three stages: (1) the input stage, in which information enters the system as signals; (2) the processing stage, in which the signals are manipulated in some way; and (3) the output stage, in which the processed signals are changed into a form that the user can understand.  Systems use various types of input and output devices that produce or respond to signals.  For example, radio and television broadcasting require such devices as microphones and loudspeakers.  From the time signals leave the input device until they reach the output device, the signals can go through a number of changes.  The electronic components working within circuits make these changes.

Electronic Circuits

In any electronic device, a circuit provides a pathway for the electric current that operates the device.  A calculator has a complex circuit.  Many of the parts of this complex circuit are actually smaller subcircuits that perform particular jobs.  Not all of the circuits necessarily work at the same time.  Certain components act as electronic "switches," turning circuits "on" and "off" as needed.  When a switch allows current to pass through a circuit, the circuit is on.  When a switch blocks current, the circuit is off.

How a Circuit Works.  To understand how an electronic circuit works, one must know something about atoms.  Every atom has one or more electrons--particles that carry a negative electric charge.  Atoms also contain protons--particles that carry a positive electric charge.  Opposite charges attract each other.  Like charges repel (push away from) each other.  Circuit operation is based on the attraction between charges.

The flow of electrons in one direction at a time forms an electric current.  Voltage, also known as electromotive force, is the "pressure" or force that drives the electrons.  In circuits, voltage is the electrical attraction caused by the difference in the charges between two points in the circuit.  A power source provides voltage.  One side of the power source supplies a negative voltage, and the other end supplies a positive voltage.  Batteries are a common power source.  Systems that plug into an electric outlet receive power from a commercial power plant.

Electrons flow from the negative voltage end of a circuit to the positive voltage end.  This movement of electrons creates an electric current.  Scientists, however, traditionally describe the direction of an electric current as flowing from positive to negative.  Until the late 1800's, scientists mistakenly believed that an electric current flowed in that direction.

Wires and certain other parts of circuits are made of materials called conductors, which can carry an electric current.  In conductors, which include metals, each atom has one or more electrons that can move from atom to atom.  These electrons are called free electrons or charge carriers.  Circuits also contain insulators, materials that block current because they have no mobile charge carriers.

As electrons move through a conductor, they collide with the atoms of the material.  Each collision hinders the flow of electrons and causes them to lose some energy as heat.  Opposition to electric current, which changes electric energy into heat, is known as resistance.

A build-up of heat can damage a circuit.  A calculator uses so little current that there is no danger of overheating.  However, some computers generate so much heat that their circuits must be continually cooled.  The whirring noise a desktop personal computer makes comes from a small fan that cools the system.

Types of Electronic Circuits.  Manufacturers make two types of electronic circuits: (1) conventional and (2) integrated.  A calculator, like most electronic devices, has both kinds.

Conventional Circuits consist of separate electronic components connected by wires and fastened to a base.  In most cases, manufacturers attach the components to a printed circuit board, a thin piece of plastic or other insulating material upon which copper "wires" are printed by a chemical process at the time of manufacture.  In a calculator, all the electronic parts of the main circuit are connected on a printed circuit board.

Integrated Circuits have components and connectors formed on and within a chip--a tiny piece of semiconductor material, usually silicon.  A semiconductor is a substance that conducts electric current better than an insulator, but not as well as a conductor.  The chip serves not only as the base but also as an essential part of the circuit.  Most chips are no larger than a fingernail.  Integrated circuits often serve as components of conventional circuits.

To make an integrated circuit, a technician prepares a large master design of the circuit with the help of a computer.  A photographic process reduces the master design to microscopic size.  Chip manufacturers treat silicon to alter its conductive properties by adding small amounts of substances called dopants, such as boron and phosphorus.  The treated regions form the chip's electronic components.  One chip can contain millions of microscopic parts connected by thin "lines" of metal.  Chip makers arrange the parts and connections in complex patterns in several layers.  Finished circuits are mounted in casings that plug into a printed circuit board.

The small size of an integrated circuit gives it several advantages over a conventional circuit.  For example, an integrated circuit works faster because the signals have less distance to travel.  Integrated circuits also need less power, generate less heat, and cost less to operate than conventional circuits.  In addition, integrated circuits are more reliable because they have fewer connections that might fail.  But strong currents and high voltages can damage integrated circuits because of their small size.

A type of integrated circuit called a microprocessor can perform all of the mathematical functions and some of the memory functions of a large computer.  Microprocessors control many products, including video games, microwave ovens, robots, and some telephones.  A microprocessor serves as the "brain" of every personal computer.  Larger computers have several microprocessors that can work together at the same time.

Electronic devices use two basic types of components within circuits to control and modify signals.  The two types are (1) electron tubes and (2) solid-state devices.

Electron Tubes

Electron tubes control the flow of electric signals through a gas or a near-vacuum.  Vacuum tubes are the most common type of electron tube.  A vacuum tube is a glass or metal container from which most of the air has been removed.  Various metallic elements within the tube produce and control beams of electrons.

From the 1920's to the 1950's, all electronic equipment used vacuum tubes.  Some equipment still uses special types of such tubes.  For example, the screen of a typical TV set is the end of a large vacuum tube called a cathode-ray tube.  Other types of vacuum tubes produce radio and radar signals, X rays, and microwaves.

Solid-State Components

Transistors and certain other electronic components are called solid-state components because the signals flow through a solid semiconductor material instead of through a vacuum.  Solid-state devices use less power, last longer, and take up less space than vacuum tubes.  Engineers developed the first successful solid-state devices during the 1940's.  Since that time, semiconductors have replaced vacuum tubes for most uses.

Most solid-state components are made of the semiconductor silicon.  Silicon and other similar semiconductors are useful because scientists can precisely adjust their resistance and thus control the flow of current through them.

To be used for electronic devices, the atoms of a semiconductor must form a crystal structure.  In these crystals, each of an atom's outer electrons pairs with an outer electron of a neighboring atom to form linkages known as electron bonds or covalent bonds.  Ordinarily, the outer electrons are tightly bound to the atoms of the crystal, and the material acts as an insulator, resisting the flow of charges.

Scientists dope (treat) pure silicon crystals with extremely small amounts of dopants to increase the silicon's ability to conduct current.  There are two types of doped semiconductors: (1) p-type, which contain mostly positive charge carriers; and (2) n-type, which contain mostly negative charge carriers.

To create p-type semiconductors, scientists add dopants whose atoms have one less outer electron than a silicon atom.  Aluminum, boron, indium, and gallium are p-type dopants.  Each impurity atom creates a hole--that is, the absence of an electron bond--in the crystal structure.  A hole acts as a positive charge, attracting electrons from neighboring atoms.  Thus, a hole can move from atom to atom.

To create n-type semiconductors, scientists add dopants whose atoms have one more outer electron than a silicon atom.  Arsenic, phosphorus, and antimony are n-type dopants.  At room temperature, the extra electron is free to move within the crystal and acts as a negative charge carrier.

Manufacturers make various electronic devices by forming different combinations of p-type and n-type semiconductors within a continuous crystal.  The place where the two types of semiconductors meet is called a p-n junction.  The number and arrangement of p-n junctions, as well as the type and amount of dopants, determine how a device works.

Diodes are electronic components that prevent current from flowing in one direction but not the other.  A semiconductor diode consists of a piece of p-type semiconductor joined to a piece of n-type semiconductor.  A diode has two terminals (metal parts for making electrical connections).  The terminals connect the end of each type of semiconductor material to the circuit.  A diode can be built into an integrated circuit, or can form a discrete (separate) component of a conventional circuit.  A discrete diode is enclosed in a protective casing.

How a Diode Works.  A diode is basically a switching device that allows current to flow in only one direction.  The current is carried by the flow of holes and electrons.  The bias (direction) of the applied voltage determines if the p-n junction blocks current or allows it to flow.

A forward bias allows current to flow through the junction.  To create a forward bias, a battery or other voltage source applies a negative voltage to the n-type material and a positive voltage to the p-type material.  The negative voltage repels the free electrons in the n-type material toward the p-n junction.  Likewise, the positive voltage repels the holes in the p-type material toward the junction.  The electrons move across the junction into the p-type semiconductor.  For each electron that crosses into the p-type material, the voltage source pumps one electron into the n-type material and pulls one electron out of the p-type material.  As a result, electrons flow through the circuit.  A small increase in the strength of the voltage causes a large increase in the current flowing through the diode.  When the voltage is removed, electron flow stops.

A reverse bias prevents most current from flowing through the p-n junction, though a small leakage current gets through.  To create a reverse bias, a voltage source applies a negative voltage to the p-type semiconductor and a positive voltage to the n-type semiconductor.  As a result, holes and electrons are attracted away from the junction.  This creates an area on either side of the junction with no mobile charge carriers.  The junction area acts as an insulator.

Uses.  Diodes are used as switches and also as rectifiers.  A rectifier circuit can change alternating current into direct current.  Alternating current reverses its direction of flow many times each second.  Direct current always flows in the same direction.  A terminal connected to a source of alternating current gets a voltage that constantly changes from positive to negative and back again.  If an alternating current is sent to a diode, the device will pass current only when the n-type semiconductor has a negative voltage.  Thus, current flows through the diode in only one direction.

Almost all commercial power plants supply alternating current.  Most electronic equipment requires direct current.  Devices that run on commercial power use diodes as rectifiers.  Devices powered by batteries do not need rectifiers because batteries produce direct current.

Transistors are arrangements of p-n junctions that can be used to amplify signals or switch a circuit on and off.  Just as a small movement of a mechanical switch can turn a powerful motor on and off, a transistor uses a small input signal to control the flow of a strong current.  A transistor can turn a current all the way on, all the way off, or partially on.  Transistors are the most important components of integrated circuits.

How a Transistor Works.  There are several types of transistors that work in different ways.  One important type is the bipolar junction transistor or bipolar transistor.  The component consists of an extremely thin layer of one type of semiconductor sandwiched between two thicker layers of the opposite type.  For example, if the middle layer is n-type, the outer layers must be p-type.  The middle region is called the base.  The outer regions are the emitter and the collector.

A bipolar junction transistor has two p-n junctions and three terminals.  Usually, two of the terminals connect the emitter and collector to an output circuit.  The third terminal connects the base to an input circuit.  Each circuit has a power source.  The power sources are arranged so that one p-n junction is forward biased and the other junction is reverse biased.

Normally, the transistor prevents current from flowing through the output circuit.  However, a small increase in voltage on the base terminal enables a large number of electrons to enter the base through the forward-biased junction.  The number of electrons entering the base varies with the strength of the voltage.  Because the base region is extremely narrow, the voltage source in the output circuit is able to attract the electrons through the reverse-biased junction.  As a result, a large current flows through the transistor and through the output circuit.  In this way, a small signal supplied to the base controls the flow of a strong current through the output circuit.

Another major type of transistor is the field effect transistor, which works in a different way than the bipolar transistor.  For more information on both types of transistors and how they work, see TRANSISTOR.

Uses.  Transistors perform three main electronic functions: (1) amplification, (2) switching, and (3) oscillation.

Amplification is the strengthening of a weak, fluctuating signal.  The current that flows through the transistor and the output circuit is basically a duplicate of the input signal--but much stronger.  A transistor can react to signal fluctuations billions of times per second.

Most electronic equipment would not work without amplifiers.  Amplifiers are used in equipment designed to transmit or process audio (sound) or video (picture) signals.  Most signals must be amplified so that they can drive an output device, such as a loudspeaker, a TV set, or a computer printer.

Amplifiers are also used to detect information.  For example, special instruments record and amplify the weak electric signals given off by the human heart and brain.  Physicians study these signals to diagnose certain injuries and diseases.

Switching is another important function of a transistor.  As a switch, a transistor turns a circuit on or off or directs the path of signals.  For a transistor to function as a switch, the strength of input signals must vary widely, so that the transistor simply turns the main supply current all the way on or off.

Oscillation converts a direct current signal to an alternating current signal of a desired frequency (number of vibrations per second).  Transistor circuits that do this are called oscillators.  An oscillator is actually a kind of amplifier that strengthens a signal and then feeds part of the amplified signal back into itself to produce its own input.  Various circuit arrangements enable a transistor to act as an oscillator.

Oscillators serve many purposes.  For example, they produce the radio waves that carry sound and pictures through space.  They also produce timing signals that control the internal operations of computers and that operate certain types of automatic machinery.  In medicine, an oscillator called a cardiac pacemaker produces carefully timed electric pulses similar to the natural pulses that make the heart beat regularly.  Surgeons implant cardiac pacemakers inside the chest of certain patients to correct an irregular heartbeat.

Passive Components

Electronic components may be divided into two categories: (1) active and (2) passive.  Active components are those that can amplify, switch, or oscillate signals.  Most electronics experts classify electron tubes, transistors, and certain diodes as active components.  Passive components either change electric energy into heat or store electric energy internally.  Passive components include resistors, capacitors, and inductors.

Resistors change electric energy into heat.  Resistors are used to reduce the amount of current flowing through a circuit.  The larger the resistor, the smaller the amount of current that flows through it.

Capacitors and inductors store electrical energy.  Electronic circuits use capacitors to store information as the presence or absence of a charge.  Capacitors are also used to block the flow of a direct current.  Inductors, on the other hand, block the flow of alternating current but allow direct current to pass.

In integrated circuits, manufacturers can adjust the semiconductor chip to create areas that act as resistors and capacitors, but not as inductors.  Inductors can be created only through complex circuitry.  Inductors can also be attached to integrated circuits as discrete components.

Electronics and Light

Many electronic devices make use of the ability of electrons to absorb and give off energy as light.  Such optoelectronic devices include light-sensing devices, light-emitting devices, and liquid crystal displays.

Light-Sensing Devices, also known as electric eyes, use light energy to produce or control an electric current.  The heart of such devices consists of a light-sensing diode, or photodiode, usually made of silicon.  A photodiode resembles an ordinary diode but has a window or lens that lets light fall onto the p-n junction.  The light knocks some electrons out of their crystal bonds, producing pairs of free electrons and holes that can flow.  Some photodiodes, such as solar cells, generate current.  Panels of solar cells power most artificial satellites and many smaller electronic devices, such as calculators.  Other photodiodes are used to switch an external power supply on and off.

Light-Emitting Devices use electric current to produce light.  Most light-emitting diodes (LED's) are made from gallium arsenide or other semiconductor compounds that give off energy in the form of light instead of heat.  As current flows through an LED, free electrons and holes near the p-n junction combine.  When a free electron "falls" into a hole, the process releases a tiny packet of light energy called a photon.  With a strong enough current, the junction area of the chip glows brightly.  Groups of LED's are used in many displays.

Semiconductor lasers are special diodes that produce an extremely narrow, powerful beam of light.  Lasers have many uses in communications, industry, medicine, and science.  For example, with fiber-optic communication, a laser beam transforms the electric signals of a telephone call or TV picture into pulses of photons.  The photon signals travel at great speeds through hair-thin strands of glass called optical fibers without losing much strength or clarity.

Liquid Crystal Displays (LCD's) are commonly used in calculators, digital watches, and laptop computers.  A thin layer of liquid crystal is sandwiched between two sheets of glass.  Normally, the display reflects light.  A voltage signal causes portions of the display to darken.  These portions form the shape of a number or letter.

How Electronic Circuits Process Information

Circuits process information by combining inputs to produce new information according to instructions.  The way a circuit processes information depends on the type of signals it works with.

Electronic circuits work with two basic types of signals: (1) digital and (2) analog.  Digital signals represent all information with a limited number of voltage signals.  Each signal has a distinct value.  Analog signals vary continuously in voltage or current, corresponding to the input information.  A fluctuating voltage can stand for changes in light, sound, temperature, pressure, or even the position of an object.

Digital Circuits process information by counting or comparing signals.  Many digital circuits can process information much faster than analog circuits.  The majority of processing is done by digital circuits.

In digital processing, all input data--words, numbers, and other information--are translated into binary numbers, which are groups of 1's and 0's.  The code is called binary (consisting of two) because only two digits are used.  Any binary number can be represented by a combination of circuits or devices that are in one of two states.  For example, a circuit can be on or off.  One state corresponds to a binary 1 and the other to a 0.  Each 1 or 0 is called a bit, a contraction of binary digit.  Many systems work with bits in groups called words.  A word that consists of 8 bits is called a byte.

Digital processing requires three basic elements: (1) memory circuits, which store data; (2) logic circuits, which change data; and (3) control circuits, which direct the operations of the system.  Wire channels called buses link the elements to each other as well as to the entire system.  A microprocessor combines these elements on one chip.

Memory Circuits store bits permanently or temporarily.  A common type of memory circuit contains thousands of capacitors arranged in rows.  The capacitors hold bits as an electric charge or the absence of a charge.  A metal conductor connects each capacitor to the system.  Transistors or diodes act as switches between the capacitors and conductors.  When a signal opens a switch, bits can travel along the conductor.  Other circuits then restore the bits by recharging the capacitors with the same sequence of charges.

There are two basic kinds of memory circuits--random-access memory (RAM) and read-only memory (ROM).  The information in RAM can be erased or added to.  RAM circuits store data only as long as the power is on.  When the power is turned off, all the stored charges are wiped out.  RAM circuits are used in such devices as computers and certain calculators, which need to store large amounts of information for brief periods.

A ROM circuit permanently stores information installed at the time of manufacture.  This information can be neither erased nor added to.  ROM generally contains instructions, or programs, for operating the system.

Not all memory is stored in circuits.  For example, computers also use external memory devices, such as magnetic disks and magnetic tapes.  Users input such memory into the system.  Another type of memory device is a compact disc, also called a CD, which stores information on a plastic platter.  A CD-ROM can store data, pictures, and sound as well as programs.

Logic Circuits, also called processors, manipulate data according to instructions.  In a processor, the bits go through a sequence of switches that change them in some way.  For example, a group of switches may add two numbers together.  Such a group is called an adder.  An adder may involve hundreds of switches.  During processing, bits are stored temporarily in areas called registers, awaiting the next instruction.

Another combination of switches can compare two bits and generate a particular output based on a set of rules established for the processor.  Such circuits use binary digits to stand for such ideas as "true" or "false," instead of 1 or 0.

Designers create areas on chips that can count or compare signals by combining small groups of circuits that make simple changes in just one or two bits.  These groups are often called logic gates.  Three basic gates are (1) the NOT-gate, (2) the AND-gate, and (3) the OR-gate.  If combined in large enough numbers, these gates can solve complex mathematical or logical problems.

A NOT-gate, also called an inverter, changes a bit from a 1 to a 0, or from a 0 to a 1.  Such a function has many uses.  For example, addition involves changing 0's to 1's and 1's to 0's.

Both AND- and OR-gates generate one output signal from two or more inputs.  An AND-gate requires that all inputs be true--often represented by a 1--to produce a true output, or a 1.  An OR-gate requires only one true input to produce a true output.

Control Circuits direct and coordinate the work of all other parts of the system according to instructions stored in the memory circuits.  One of the main jobs of the control circuit is to control the movement of bits through the system.  To do this, an oscillator called the clock generates continuous pulses.  The bits move through the circuit according to the rhythm of the clock.

Analog Circuits solve problems by measuring continuously varying quantities, such as temperature, speed, and pressure.  Many familiar devices, including speedometers and thermometers, work as analog computers.  Small analog circuits are parts of many electronic systems that control the operations of other machines.  Analog circuits are also used in navigation equipment.

Digital-Analog Conversion.  Some circuits can convert analog signals into digital signals, and digital into analog.  In digital sound recording, for example, the amplitude (strength) of the sound wave is measured thousands of times every second and converted into a digital code signal made up of rapid bursts of current.  To play the resulting digital signals, a sound system converts them back to analog signals that drive a loudspeaker.  Digital signals produce better sound quality with less background noise and distortion than analog signals.

The Electronics Industry

The development, manufacture, and sales of electronic products make up one of the largest and most important industries in the world.  The electronics industry is also one of the fastest-growing of all industries.

Research and Development.  Engineers and scientists at research laboratories work to add new knowledge about electronics and to develop new electronic devices.  In the United States, a number of universities and electronics companies maintain research laboratories.  In 1982, many large manufacturers and users of computer chips formed a nonprofit organization called the Semiconductor Research Corporation to support basic research on electronics at universities.

The U.S. government sponsors electronics research through such agencies as the National Science Foundation, the National Aeronautics and Space Administration, and the Department of Energy.  The government also sponsors research through its military branches.  In addition, the electronics industry and the government combine research efforts through the Semiconductor Manufacturing Technology Institute, better known as SEMATECH. The government and 14 electronics companies founded SEMATECH in 1987 to help U.S. chip makers become more competitive in manufacturing.

Manufacturing and Sales.  The United States and Japan are the world's largest producers of electronic components and assembled electronic products.  In the early 1990's, electronics companies in the United States employed more than 1 1/2 million workers.  The sales of United States electronics companies totaled about $300 billion each year.  During the same period, electronics companies in Japan employed about 2 million workers.  The Japanese firms had total sales valued at about $190 billion.  Other leading producers of electronic equipment include Canada, Germany, the Netherlands, Singapore, South Korea, Taiwan, and the United Kingdom.

Careers in Electronics can be divided into two main groups.  They are (1) engineering and scientific careers and (2) technical careers.

Engineering and Scientific Careers range from developing new electronic devices to designing computers.  Most of these careers require a college degree in engineering or physics.  The Information Finder articles on ENGINEERING and PHYSICS discuss the requirements for becoming an electrical engineer and a physicist.

Most engineers and physicists who specialize in electronics work for electronics companies.  Some of these companies do most or all of their work on military projects.  Other engineers and physicists find jobs with the federal government, at colleges and universities, and in communication, medicine, or transportation.

Technical Careers in electronics usually involve installing, operating, maintaining, or repairing electronic equipment.  Many technical jobs require training in a trade school or community college.  Such technical careers include automation control, computer programming, television repair, and X-ray technology.

Other technical jobs require only on-the-job training.  Such jobs include operating certain types of electronic equipment in factories and offices.  Some highly skilled technical jobs in the aerospace and communications industries require a college degree.  Many people receive technical electronics training in the armed forces.

The Development of Electronics

Early Experiments.  During the mid-1800's, scientists experimented with gas-discharge tubes--that is, tubes from which some of the air had been removed, leaving a thin mixture of gases.  Most of these tubes contained a combination of such gases as hydrogen and nitrogen at low pressure.  Scientists discovered electric current could pass through the gas from one metal electrode (terminal) to another.  When a battery was connected to the two electrodes, the tube glowed with bright colors.  Scientists believed that the cathode--the negative electrode--gave off invisible rays that caused the colors.  They named the rays cathode rays.  As scientists removed still more air from the tubes for their experiments, the tubes became vacuum tubes.

In 1879, Sir William Crookes, a British scientist, developed a tube to study cathode rays.  The Crookes tubes were forerunners of television picture tubes.

In 1895, German physicist Wilhelm C. Roentgen discovered X rays while studying cathode rays in a Crookes tube.  By the end of the 1800's, many doctors were using X-ray photographs to diagnose internal diseases and injuries in their patients.

In 1897, the British physicist Joseph J. Thomson proved that cathode rays consist of negatively charged particles, later named electrons.  Thomson's discovery led to the first practical electronic devices.

During the early 1900's, electrical engineers developed vacuum tubes that could detect, amplify, and create radio signals.  In 1907, the American inventor Lee De Forest patented a three-electrode, or triode, vacuum tube.  The triode tube became a key element in radio broadcasting and reception because it could amplify signals.  Commercial radio broadcasting began in 1920, and the electronics industry was born.  By 1927, more than 5 million American homes had radios.

The Vacuum Tube Era lasted from the 1920's to the 1950's.  During this period, vacuum tubes made possible such electronic inventions as television, radar, and computers.

As early as 1875, American scientist G. R. Carey had built a photoelectric cell, a device that produced an electric current when light shone on it.  Carey's invention operated on the same principle as a TV camera, but it was not put to practical use until the early 1920's.  In 1923, a Russian-born American scientist named Vladimir K. Zworykin made the first successful television camera tube.  Using a cathode-ray tube as a model, Zworykin also developed a workable television picture tube during the 1920's.  Experimental telecasts began in the late 1920's, but TV broadcasting did not begin on a large scale until the late 1940's.

In 1921, Albert W. Hull, an American engineer, invented a vacuum tube oscillator called a magnetron.  The magnetron was the first device that could efficiently produce microwaves.  Radar, which was developed gradually during the 1920's and 1930's, provided the first widespread use of microwaves.

The vacuum tube era reached its peak with the completion of the first general-purpose electronic computer in 1946.  This huge machine, called ENIAC (Electronic Numerical Integrator And Computer), was built by two engineers at the University of Pennsylvania, J. Presper Eckert, Jr., and John W. Mauchly.  The computer contained about 18,000 vacuum tubes and occupied about 1,800 square feet (170 square meters) of floor space.  ENIAC worked 1,000 times faster than the fastest nonelectronic computers then in use.

The Solid-State Revolution.  Three American physicists--John Bardeen, Walter H. Brattain, and William Shockley--invented the transistor in 1947.  Transistors revolutionized the electronics industry, dramatically reducing the size of computers and other equipment.  Transistors were used as amplifiers in hearing aids and pocket-sized radios in the early 1950's.  By the 1960's, semiconductor diodes and transistors had replaced vacuum tubes in much equipment.
 
 

Integrated circuits developed from transistor technology as scientists sought ways to build more transistors into a circuit.  The first integrated circuits were patented in 1959 by two Americans--Jack Kilby, an engineer, and Robert Noyce, a physicist--who worked independently.  Integrated circuits caused as great a revolution in electronics in the 1960's as transistors had caused in the 1950's.  The circuits were first used in military equipment and spacecraft and helped make possible the first manned space flights of the 1960's.

The first microprocessors were produced in 1971 for desktop calculators.  By the mid-1970's, microprocessors were being used in handheld calculators, video games, and home appliances.  Business and industry began to use microprocessors to control various types of office machines, factory equipment, and other devices.

Electronics Today.  Scientists and engineers continue to search for ways to make electronic circuits smaller, faster, and more complex.  Developing technologies include superconductors and photonics.

Superconductors are materials that lose all resistance to the flow of current at low temperatures.  Superconductor devices operate extremely fast and produce almost no heat.  Scientists are testing superconducting switching devices to control computer circuits.

Photonics is the science of building circuits that use photons--tiny packets of light energy--as signals instead of electrons.  Photonic circuits use pulsed beams of photons to transmit data and commands through optical fibers.  Photonic circuits can carry huge amounts of information, and they produce no heat.  Today, the enormous information-carrying capacity of optical fibers is opening a new era in home entertainment, communications, and computer technology.

Display techniques in electronics are also rapidly changing.  Manufacturers are developing flatter display panels to replace the bulky cathode-ray tubes used in television and many computer screens.  One new design, introduced in 1993, uses thousands of tiny tubes side by side to form a picture.  The screen is less than 4 inches (10 centimeters) thick.  Another technology relies on even flatter LCD panels.  These lightweight, energy-saving screens could hang on a wall like a picture.  Today, portable computers such as laptop and notebook computers commonly use flat LCD screens.

In the early 1990's, manufacturers began to use a new type of liquid crystal display called the active matrix LCD in portable computers, video games, and other electronic products.  In these displays, thousands of transistors on the inner surface of the glass control the signals that activate the liquid crystal.