Electronics

Electronics is the important branch of physics that deals with the study of the motion and control of electrons and study of their behavior in vacuums, semiconductors, and gasses and with devices using such types of electrons. This type of control of electrons is done by devices that resist, carry, select, switch, store, manipulate, and exploit the electrons.

In this page we will explain:

  1. Introduction
  2.  Historical background
  3.  Frequently used electronic circuits
  4.  Sound amplifiers
  5.  Logic circuits
  6. Recent advances
  7. Introduction

The electronics is the field of engineering and physics applied on the design and application of devices, usually circuit electronics, whose operation depends on the flow of electrons for generation, transmission, reception, storage of information  , among others. This information may consist of voice or music such as a radio receiver , an image on a television screen , or numbers or other data on a computer or computer .

Electronic circuits offer different functions to process this information, including amplification of weak signals to a level that can be used; generating radio waves ; the extraction of information, such as the recovery of the sound signal of a radio wave (demodulation); the control , as in the case of introducing a sound signal to radio waves ( modulation ), and logical operations , such as electronic processes that take place in computers .

  1. Historical background

The introduction of vacuum tubes in the early twentieth century led to the rapid growth of modern electronics. With these devices it was possible to manipulate signals, something that could not be done in the old telegraph and telephone circuits, nor with the first transmitters that used high voltage sparks to generate radio waves. For example, with the vacuum tubes the weak radio and sound signals could be amplified, and also sound signals could be superimposed on the radio waves. The development of a wide variety of tubes, designed for specialized functions, enabled the rapid advancement of communication technologyradio before  World War II , and the development of the first computers, during the war and shortly after it.

Today, the transistor , invented in 1948, has almost completely replaced the vacuum tube in most of its applications. By incorporating a set of semiconductor materials and electrical contacts, the transistor allows the same functions as the vacuum tube, but with a lower cost, weight and power , and greater reliability. Subsequent progress in semiconductor technology, partly attributable to the intensity of research associated with the space exploration initiative, led to the development, in the 1970s, of the integrated circuit. These devices can contain hundreds of thousands of transistors on a small piece of material, allowing the construction of complex electronic circuits, such as microcomputers or microcomputers, audio and video equipment, and satellites for communications .

  1. Electronic components

Electronic circuits consisting of interconnected electronic components. These speakers are classified into two categories: assets or liabilities. Liabilities include resistors , capacitors and coils. Those considered active include batteries (or batteries ), generators, vacuum tubes and transistors.

Empty tubes

A vacuum tube consists of a glass capsule from which the air has been extracted , and which carries several metal electrodes inside. A simple two-element tube (diode) is formed by a cathode and an anode, the latter connected to the positive terminal of a power supply . The cathode (a small metal tube that is heated by a filament) releases electrons that migrate to it (a metal cylinder around to the cathode, also called plaque). If an alternating voltage is applied to the anode, the electrons will only flow to the anode during the positive half cycle; During the negative cycle of alternating voltage, the anode repels electrons, preventing any current from passing through the tube. The diodes connected in such a way that they only allow the positive half-cycles of an alternating current (AC) are called rectifier tubes and are used in the conversion of alternating current to direct current (DC). By inserting a grid, formed by a spiral metallic wire, between the cathode and the anode, and applying a negative voltage to said grid, it is possible to control the flow of electrons. If the grid is negative, it repels them and only a small fraction of the electrons emitted by the cathode can reach the anode. This type of tube, called a triode, can be used as an amplifier. Small variations in the voltage that occur in the grid, such as those generated by a radio or sound signal, can cause large variations in the flow of electrons from the cathode to the anode and, consequently, in the system of circuits connected to the anode.

Transistors

Transistors are composed of semiconductors. These are materials, such as silicon or germanium, doped (that is, they have embedded small amounts of foreign matter with chemical reactions), so that there is an abundance or lack of free electrons. In the first case, the semiconductor is said to be of type n, and in the second it is of type p. Combining materials of type n and type p can produce a diode. When it is connected to a battery so that the p-type material is positive and the n-type material is negative, the electrons are repelled from the negative terminal of the battery and pass, without any obstacle, to the region p, which lacks of electrons With the battery inverted, the electrons that reach the material p can pass only with many difficulties towards the material n, which is already full of free electrons, in which case the current is almost zero.

The bipolar transistor was invented in 1948 to replace the triode vacuum tube. It consists of three layers of doped material, which form two pn (bipolar) junctions with pnp or npn configurations. One junction is connected to the battery to allow current flow (front negative polarization, or direct polarization), and the other is connected to a battery in the opposite direction (reverse polarization). If the current in the direct polarization junction is varied by the addition of a signal, the current of the reverse polarization junction of the transistor will vary accordingly. The principle can be used to build amplifiers in which a small signal applied to the direct polarization junction will cause a large change in the reverse polarization junction current.

Another type of transistor is that of field effect (FET, English acronym for Field-Effect Transistor), which operates on the basis of the principle of repulsion or attraction of charges due to the superposition of an electric field . The amplification of the current is achieved in a manner similar to that used in the grid control of a vacuum tube. Field effect transistors work more efficiently than bipolar ones, since it is possible to control a large signal with a very small amount of energy.

Integrated circuits

Most of the integrated circuits are small pieces, or chips, of silicon, between 2 and 4 mm2, on which the transistors are manufactured. Photolithography allows the designer to create hundreds of thousands of transistors on a single chip, properly positioning the numerous regions type n and p. During manufacturing, these regions are interconnected by tiny conductors, in order to produce complex specialized circuits. These integrated circuits are called monolithic because they are manufactured on a single silicon crystal. The chips require much less space and power, and their manufacturing is cheaper than that of an equivalent circuit composed of individual transistors.

Resistors

When a battery is connected to a conductive material, a certain amount of current will flow through that material. This current depends on the battery voltage, the dimensions of the sample and the conductivity of the material itself. The resistors are used to control the current in the electronic circuits. They are made with mixtures of carbon , metal sheets or resistance wire, and have two connection cables. Variable resistors are called rheostats or potentiometers, with a sliding and adjustable contact arm, often used to control the volume of radios and televisions.

Condensers

The capacitors are formed by two metal plates separated by an insulating material. If a battery is connected to both boards, an electric current will flow for a short time that will accumulate in each of them. If the battery is disconnected, the capacitor retains the charge and the voltage associated with it. Rapidly changing voltages, such as those caused by a sound or radio signal, generate greater current flows to and from the plates; then, the capacitor acts as a conductor of the alternating current. This effect can be used, for example, to separate a sound or radio signal from a direct current, in order to connect the output of one amplification phase to the input of the next.

Coils

The coils (also called inductors) consist of a coiled conductor wire. When a current passes through the coil, around it a magnetic field is created that tends to oppose sudden changes in the intensity of the current. Like a capacitor, a coil can be used to differentiate between fast and slowly changing signals (high and low frequencies). When using a coil in conjunction with a capacitor, the coil voltage reaches a maximum value at a specific frequency that depends on the capacitance and inductance. This principle is used in radio receivers when selecting a specific frequency using a variable capacitor.

Detection devices and transducers

The measurement of mechanical, thermal, electrical and chemical quantities is performed using devices called sensors and transducers. The sensor is sensitive to changes in the magnitude to be measured, such as a temperature , a position or a chemical concentration . The transducer converts these measurements into electrical signals, which can feed reading , recording or control instruments of the measured quantities. Sensors and transducers can operate in locations far from the observer, as well as in environments that are inappropriate or impracticable to humans.

Some devices act simultaneously as a sensor and transducer. A thermocouple consists of two unions of different metals that generate a small voltage that depends on the differential term between the joints. The thermistor is a special resistor, whose resistance value varies according to the temperature. A variable rheostat can convert the mechanical movement into an electrical signal. Specially designed capacitors are used to measure distances, and photocells are used to detect light . To measure speeds, acceleration or liquid flows, other devices are used. In most cases, the electrical signal is weak and must be amplified by an electronic circuit.

  1. Frequently used electronic circuits

Power supply circuits ( Sources )

Most electronic equipment requires DC voltages for operation. These voltages can be supplied by batteries or by internal power supplies that convert the alternating current, which can be obtained from the mains that reach each home, into regulated DC voltages. The first element of an internal DC power supply is the transformer, which raises or lowers the input voltage to a level suitable for the operation of the equipment. The function secondary of the transformer is used as insulation mass (connection to earth) electrical device to reduce possible electrocution hazards. Next to the transformer is a rectifier, which is usually a diode. In the past, vacuum diodes and a wide variety of different materials (germanium crystals or cadmium sulfate) were used in the low power rectifiers used in electronic equipment. Currently, silicon rectifiers are used almost exclusively due to their low cost and high reliability.

The fluctuations and undulations superimposed on the rectified DC voltage (perceived as a buzz in the defective sound amplifiers) can be filtered by a condenser. The larger the capacitor, the lower the level of voltage fluctuation. It is possible to achieve more precise control over voltage levels and fluctuations by means of a voltage regulator, which also makes internal voltages independent of fluctuations that may be found in an electrical appliance. A simple voltage regulator that is often used is the Zener diode, formed by a status pn junction diode solid that acts as an insulator up to a predetermined tension. Above that voltage, it becomes a conductor that derives excess voltage. Typically, the most sophisticated voltage regulators are built as integrated circuits .

Amplifier circuits

Electronic amplifiers are used primarily to increase the voltage, current or power of a signal. Linear amplifiers increase the signal without distorting it (or minimally distorting it), so that the output is proportional to the input. Non-linear amplifiers allow a considerable change in the waveform of the signal to be generated. Linear amplifiers are used for sound and video signals, while non-linear amplifiers are used in oscillators, electronic power devices, modulators, mixers, logic circuits and other applications where amplitude reduction is required. Although the vacuum tubes were of great importance in the amplifiers,

  1. Sound amplifiers

Sound amplifiers, commonly used in radios, televisions and tape recorders, usually operate at frequencies between 2 and 20 kiloherz (1 kHz = 1,000 cycles per second). They amplify the electrical signal that is then converted into sound with a speaker. Operational amplifiers, incorporated in integrated circuits and formed by multiphase linear amplifiers coupled to direct current, are very popular as sound amplifiers.

Video amplifiers

Video amplifiers are mainly used for signals with a frequency range of up to 6 megaherz (1 MHz = 1 million cycles per second). The signal generated by the amplifier becomes the visual information, for example, the one that appears on the television screen , and the signal amplitude regulates the brightness of the points that form the image. To perform this function, a video amplifier must operate in a broadband and amplify all signals equally, with low distortion.

Radio frequency amplifiers

These amplifiers increase the signal level of communications systems

of radio or television. In general, their frequencies range from 100 kHz to 1 gigaherz (1 GHz = 1 billion cycles per second), and can even reach the microwave frequency range .

Oscillators

The oscillators consist of an amplifier and some kind of feedback: the output signal is redirected to the amplifier input. The frequency determining elements may be a tuned inductance-capacitance circuit or a vibrating crystal. Crystal controlled oscillators offer greater precision and stability. Oscillators are used to produce sound and radio signals in a wide variety of uses. For example, simple radio frequency oscillators are used in modern key phones to transmit data to the central telephone station when dialing a number. The sound tones generated by the oscillators can also be found in alarm clocks, radios, electronic instruments, computers and alarm systems. High frequency oscillators are used in communications equipment to control the tuning and signal detection functions. Radio and television stations use high-frequency and high-precision oscillators to generate the transmission frequencies.

  1. Logic Circuits

The switching and timing circuits, or logical circuits, form the basis of any device in which signals have to be selected or combined in a controlled manner. The fields of application of these types of circuits include telephone switching, satellite transmissions and the operation of digital computers.

The logic digital is a process rational decisions to adopt simple ‘true’ or ‘false’ based on the rules of the algebra of Boole. The state true is represented by a 1, and false by a 0, and in the logic circuits these numerals appear as signals of two different voltages. Logic circuits are used to make specific ‘true-false’ decisions based on the presence of multiple ‘true-false’ signals at the inputs. The signals can be generated by mechanical switches or by solid state transducers. The input signal, once accepted and conditioned (to eliminate unwanted electrical signals, or noise), is processed by the digital logic circuits. The various families of digital logic devices, usually integrated circuits, perform a variety of logical functions through the so-called logic gates, such as OR gates, AND and NOT and combinations thereof (such as ‘NOR’, which includes OR and NOT). Otherwidely used logic family is transistor-transistor logic. The complementary metal oxide semiconductor logic is also used, which performs similar functions at very low power levels but at slightly lower operating speeds. There are also many other varieties of logic circuits, including the obsolete rheostat-transistor logic and transmitter coupling logic, used for very high speed systems.

The elementary blocks of a logical device are called digital logic gates. A Y (AND) gate has two or more entrances and a single exit. The exit of a door And is true only if all the entrances are true. An O (OR) door has two or more entrances and a single exit. The exit of a door O is true if any of the entries is true, and is false if all the entries are false. An INVERTER gate has a single input and a single output, and can convert a true signal to a false one, thus performing the negation (NOT) function. From the elementary doors, more complicated logic circuits can be constructed, among which the flip-flop circuits (also called flip-flops, which are binary switches), counters,

In general, to execute a certain function it is necessary to connect large quantities of logical elements in complex circuits. In some cases microprocessors are used to perform many of the switching and timing functions of the individual logic elements. The processors are specifically programmed with individual instructions to execute a certain task or tasks. One of the advantages of microprocessors is that they allow different logical functions to be performed, depending on the programming instructionsstored The disadvantage of microprocessors is that they usually work sequentially, which could be too slow for some applications. In such cases, specially designed logic circuits are used.

  1. Recent advances

The development of integrated circuits has revolutionized the fields of communications, information management and information technology . The integrated circuits have allowed reducing the size of the devices with the consequent decrease in the manufacturing and maintenance costs of the systems. At the same time, they offer greater speed and reliability. Digital clocks, laptops and electronic games are microprocessor based systems. Another important advance is the digitization of sound signals, a process in which the frequency and amplitude of a sound signal is digitally encoded by techniques of sampling appropriate, ie, techniques for measuring the amplitude of the signal at very short intervals. Digitally recorded music, such as compact discs, is characterized by fidelity that was not possible to achieve with direct recording methods .

Medical electronics have reached systems that can further differentiate the organs of the human body . Devices have also been developed that allow blood vessels and the respiratory system to be seen. The high definition also promises to replace numerous photographic processes by eliminating the need to use silver.

Current research aimed at increasing the speed and capacity of computers focuses primarily on the improvement of integrated circuit technology and the development of even faster switching components. Large-  scale integrated circuits have been built that contain several hundred thousand components on a single chip. Computers that reach very high speeds have been manufactured at which semiconductors are replaced by superconducting circuits that use Josephson’s junctions and operate at temperatures close to absolute zero.

 

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