Electronic circuits

Components. Electric feeding. Amplifiers. Commutation. Delay

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Electronic, field of the engineering and of the relative applied physics to the design and application of devices, in general electronic circuits whose operation depends on the flow of electrons for the generation, transmission, reception and storage of information. This information can consist on voice or music (voice signs) in a radio receiver, in an image in a television screen, or in numbers or other data in a computer or computer.

The electronic circuits offer different functions to process this information, including the amplification of weak signs until an usable level; the generation of radio waves; the extraction of information, I eat the recovery of the sign of sound of a radio wave for example (demodulate); the control, like in the case of the overlapping of a sound sign to radio waves (modulation), and logical operations, as the electronic processes that take place in the computers.


The introduction of the hole tubes at the beginning of the XX century propitiated the quick growth of the modern electronics. With these devices it became possible the manipulation of signs, something that could not be carried out in the old telegraphic and phone circuits, neither with the first transmitters that used sparks of high tension to generate radio waves. For example, with the hole tubes the radio signs could be amplified and of weak sound, and sound signs could also be superimposed to the radio waves. The development of a wide variety of tubes, designed for specialized functions, facilitated the express it advances of the technology of radial communication before the II Guerra World cup, and the development of the first computers, during the war and soon after of her.

Nowadays, the transistor, invented in 1948, it has replaced almost completely to the hole tube in most of their applications. When incorporating a group of material semiconductors and electric contacts, the transistor allows the same functions that the hole tube, but with a cost, weight and lower power, and a bigger reliability. The subsequent progresses in the technology of semiconductors, attributable partly to the intensity of the investigations associated with the initiative of exploration of the space, it took to the development, in the decade of 1970, of the integrated circuit. These devices can contain hundreds of thousands of transistors in a small material piece, allowing the construction of complex electronic circuits, as those of the microcomputers or microcomputers, sound systems and videotape, and satellites of communications.


The electronic circuits consist of interconnected electronic components. These components are classified in two categories: active or passive. Among the passive ones the rheostat, the condensers and the inductive ones are included. Those considered assets include the batteries (or you pound), the generators, the hole tubes and the transistors.

3.1 hole tubes

A hole tube consists on a glass capsule of which the air has been extracted, and that it takes in its interior several metallic electrodes. A simple tube of two elements (diode) it is formed by a cathode and an anode, this last one connected to the positive terminal of a feeding source. The cathode (a small metallic tube that warms by means of a filament) it liberates electrons that are dispersed toward him (a metallic cylinder around the cathode, also called badge). If an alternating tension is applied to the anode, the electrons will only flow toward the anode during the positive cycle; during the negative cycle of the alternating tension, the anode repels the electrons, preventing that any current passes through the tube. The connected diodes in such a way that only allow the positive cycle of an alternating current (c.a.) they are denominated tubes rectifiers and they are used in the conversion of alternating current to continuous current (c.c.). When inserting a grill, formed by a metallic thread in hairspring, between the cathode and the anode, and applying a negative tension to this grill, it is possible to control the flow of electrons. If the grill is negative, it repels them and a small fraction of the electrons emitted by the cathode can only arrive to the anode. This tube type, denominated triode, you can use as amplifier. The small variations of the tension that take place in the grill, as those generated by a radio sign or of sound, they can cause big variations in the flow of electrons from the cathode toward the anode and, in consequence, in the connected system of circuits to the anode.

3.2 Transistors

The transistors are composed of semiconductors. It is materials, as the silicon or the germanium, dopados (that is to say, they have been incrusted small quantities of strange matters), so that he/she takes place an excess or a lack of free electrons. In the first case, it is said that the semiconductor is of the type n, and in the second that is of the type p. Combining materials of the type n and of the type p a diode can take place. When this is connected to a battery in a such way that the material type p is positive and the material type n is negative, the electrons are repelled from the negative terminal of the battery and they happen, without any obstacle, to the region p that lacks electrons. With the invested battery, the electrons that arrive to the material p can only pass with many difficulties toward the material n that is already full with free electrons, in which case the current is practically zero.

The bipolar transistor was invented in 1948 to substitute to the tube of empty triode. It is formed by three material layers full with sludges that form two unions pn (bipolar) with configurations pnp or npn. An union is connected to the battery to allow the current flow (front negative polarization, or direct polarization), and the other one is connected to a battery in contrary sense (inverse polarization).

If the current is varied in the union of direct polarization by means of the addition of a sign, the current of the union of inverse polarization of the transistor will vary in consequence.

The principle you can use to build amplifiers in those that a small sign applied to the union of direct polarization will cause a great change in the current of the union of inverse polarization.

Another transistor type is that of effect field (FET, Field Effect Transistor) that works on the base of the principle of repulsion or of attraction of loads due to the overlapping of an electric field. The amplification of the current is gotten from a similar way to the employee in the control of grill of a hole tube. The transistors of effect field work in a more effective way that the bipolar ones, since it is possible to control a big sign with a quantity of very small energy.

3.3 Integrated circuits

Most of the integrated circuits are small pieces, or tinily, of silicon, of between 2 and 4 mm2, on those that the transistors are manufactured. The photoengraving allows the designer to create hundreds of thousands of transistors in a single tinily locating in an appropriate way the numerous regions type n and p. During the production, these regions are interconnected by means of minuscule drivers, in order to produce complex specialized circuits. These integrated circuits are called monolithic to be manufactured on an only silicon glass. The tinily requires much less space and power, and their production is cheaper than that of an equivalent circuit composed by individual transistors.

3.4 rheostat

When connecting a battery to a conductive material, a certain quantity of current will flow through this material. This current depends on the tension of the battery, of the dimensions of the sample and of the conductivity of the own material. The rheostat of well-known resistance is used to control the current in the electronic circuits. They are elaborated with mixtures of carbon, metallic sheets or resistance thread, and they have two connection cables. The variable rheostat, with an arm of contact glidant and adjustable, they are usually used to control the volume of radio apparatuses and television.

3.5 Condensers

The condensers are formed by metallic two badges separated by an insulating material. If a battery is connected to both badges, during a brief time an electric current that will accumulate in each one of them will flow. If the battery, the condenser is disconnected it conserves the load and the tension associated to the same one. The quickly changing tensions, as the provoked ones for a sound sign or of radio, they generate bigger current flows toward and from the badges; then, the condenser acts as driver of the alternating current. This effect you can use, for example, to separate a sound sign or of radio of a continuous current, in order to connect the exit from an amplification phase to the entrance of the following one.

3.6 inductive components

The inductive components consists on a conductive thread wound in reel form. When passing a current through the reel, around the same one a magnetic field is believed that spreads to oppose you to the abrupt changes of the intensity of the current. the same as a condenser, is used to differ among quick and slowly changing signs. When using it jointly with a condenser, their tension reaches a maximum value to a specific frequency that depends on the capacity of the condenser and of the inductance. This principle is used in the radio receivers when selecting a specific frequency by means of a variable condenser.

3.7 detection devices and transducers

The mensuration of mechanical, thermal, electric and chemical magnitudes is carried out using devices denominated sensors and transducers. The sensor is sensitive to the changes of the magnitude to measure, like a temperature, a position or a chemical concentration. The transducer transforms these mensurations into electric signs that can feed to reading instruments, registration or control of the measured magnitudes. The sensors and transducers can work in locations far from the observer, as well as in inadequate or impracticable environments for the human beings.

Some devices act in a simultaneous way as sensor and transducer. A variable rheostat can transform the mechanical movement into electric sign. To measure distances condensers of special design they are used, and to detect the light fotocells they are used to measure speeds, accelerations or flows of liquids it is appealed to another type of devices. In most of the cases, the electric sign is weak and it should be amplified by an electronic circuit.


Most of the electronic teams require tensions of c.c. for their operation. These tensions can be given by batteries or for internal feeding sources that convert the alternating current that one can obtain of the electric net that arrives to each housing, in regulated tensions of c.c. The first element of a source of feeding of c.c. it interns it is the transformer that rises or it diminishes the entrance tension at an appropriate level for the operation of the team. The secondary function of the transformer is to serve as isolation of mass (connection to earth) electric of the device in order to reduce possible electrocution dangers. After the transformer a rectifier is located that is usually a diode. In the past hole diodes and a wide variety of different materials were used (germanium glasses or sulfate of cadmium) in the rectifiers of low power used in the electronic teams. At the present time they are used silicon rectifiers almost exclusively due to their low cost and high reliability.

The fluctuations and waves superimposed to the tension of c.c. rectified (perceived as a buzzing in the faulty sound amplifiers) they can filter by means of a condenser. The more big it is the condenser, minor it will be the level of fluctuation of the tension. It is possible to reach a more exact control on the levels and fluctuations of tension by means of a regulator of tension that also gets that the internal tensions are independent of the fluctuations that they can be in an electric device. A simple regulator of tension that is often used is the diode Zener, formed by a diode of union pn of solid state that it acts as insulating until a predetermined tension. Above this tension, he/she becomes a driver that derives the excesses of tension. In general, the most sophisticated regulators of tension are built as integrated circuits.


The electronic amplifiers are used mainly to increase the tension, the current or the power of a sign. The lineal amplifiers increase the sign without distorting it (or distorting it minimumly), so that the exit is proportional to the entrance. The non lineal amplifiers allow to generate a considerable change in the form of wave of the sign. The lineal amplifiers are used for sound signs and videotape, while those not lineal they are used in oscillators, electronic devices of feeding, modulators, mixers, circuits logical and other applications in those that a reduction of the width is required. Although the hole tubes had great importance in the amplifiers, nowadays circuits of discreet transistors or integrated circuits are usually used.

5.1 sound amplifiers

The sound amplifiers, of common use in radios, televisions and recorders of tapes, they usually work to inferior frequencies to the 20 kilohertz (1 kHz = 1.000 cycles per second). they Amplify the electric sign that, next, he/she becomes sound with a speaker. The operative amplifiers, incorporated in integrated circuits and formed by amplifiers lineal multiphases coupled to the continuous current, they are very popular as sound amplifiers.

5.2 videotape amplifiers

The videotape amplifiers are used mainly for signs with a range of frequencies of up to 6 megahertz (1 MHz = 1 million cycles per second). The sign generated by the amplifier becomes the visual information that appears in the television screen, and the sign width regulates the shine of the points that form the image. To carry out this function, a videotape amplifier should work in a wide band and to amplify in a same way all the signs, with low distortion.

5.3 radiofrequency amplifiers

These amplifiers increase the level of sign of the systems of radio communications or television. In general, their frequencies go from 100 kHz to 1 gigahertz (1 GHz = 1.000 million cycles per second), and they can even arrive to the range of frequencies of microwaves.


The oscillators consist of an amplifier and of some feedback type: the exit sign diminishes when entering in the amplifier. The decisive elements of the frequency can be a circuit of inductance-capacitancia syntonized or a vibrant glass. The oscillators controlled by glass offer bigger precision and stability. The oscillators are used to produce sound signs and of radio with a wide variety of uses. For example, the simple oscillators of radiofrequency are used in the modern telephones of bellboys to transmit data to the central phone station when marking a number. The sound tones generated by the oscillators can also be in clocks alarm clocks, radios, electronic instruments, computers and alarm systems. The oscillators of high frequency are used in teams of communications to control the tuner functions and detection of signs. The radio radio stations and of television they use oscillators of high frequency and of great precision to generate the transmission frequencies.


The commutation circuits and delay, or logical circuits, form the base of any device in which you/they are had to select or to combine signs in a controlled way. Among the fields of application of these circuits they can be mentioned the phone commutation, the transmissions for satellite and the operation of the digital computers.

The digital logic is a rational process to adopt simple decisions of "true" or "false" based on the rules of the algebra of Boole. True it can be represented by a 1, and false for a 0, and in the logical circuits these numeral ones appear like signs of two different tensions. The logical circuits are used to adopt specific decisions of "true-false" on the base of the presence of multiple signs "true-false" in the entrances. The signs can be generated by mechanical switches or for transducers of solid state. The entrance sign, once accepted and conditioned (to not eliminate the electric signs wanted, or noises), it is processed by the digital logical circuits. The diverse families of digital logical devices, in general integrated circuits, they execute a variety of logical functions through the calls logical doors, as the doors OR, AND and NOT and combinations of the same ones (as NOR that includes OR and NOT). Another very used logical family is the logical transistor-transistor. The logic of complementary semiconductor of metallic oxide is also used that executes similar functions at very low levels of power but lightly inferior operation speeds. Also many exist other varieties of logical circuits, including the today obsolete logical reóstato-transistor and the joining logic for originator, used for systems of very high speeds.

The elementary blocks of a logical device are denominated digital logical doors. A door AND (AND) he/she has two or more entrances and an only exit. The exit of a door AND it is true only if all the entrances are true. A door OR (OR) he/she has two or more entrances and a single exit. The exit of a door OR it is true if anyone of the entrances is true, and it is false if all the entrances are false. A door investor has an only entrance and an only exit, and it can convert a true sign in false, making this way the function negation (NOT). starting from the elementary doors more complicated logical circuits can be built, among those that it is necessary to mention the circuits flip-flops that are binary switches), accountants, comparatives,adder, and more complex combinations.

In general, to execute a certain function it is necessary to connect big quantities of logical elements in complex circuits. In some cases microprocessors are used to make many of the commutation functions and delay of the elements logical singular. The processors are specifically programmed with individual instructions to execute a certain task or tasks. One of the advantages of the microprocessors is that they allow to carry out different logical functions, depending on the stored programming instructions. The disadvantage of the microprocessors is that they usually work in a sequential way, what could be too slow for some applications. In such cases specially designed logical circuits are used.


The development of the integrated circuits has revolutionized the fields of the communications, the administration of the information and the computer science. The integrated circuits have allowed to reduce the size of the devices with the rising descent of the costs of production and of maintenance of the systems. At the same time, they offer bigger speed and reliability. The digital clocks, the laptops and the electronic games are systems based on microprocessors. Another important advance is the digitization of the sound signs, process in the one which the frequency and the width of a sound sign is coded digitally by means of technical of appropriate sampling, that is to say, techniques to measure the width from the sign to very short intervals. The recorded music in a digital way, as that of the compact disks, it is characterized by a fidelity that was not possible to reach with the methods of direct recording.

The medical electronics has progressed from the on-line axial tomografía (TAC) until arriving to systems that can differ even more the organs of the human body. They have been developed devices that allow to see the sanguine glasses and the breathing system also. The high definition also promises to substitute to numerous photographic processes when eliminating the necessity to use silver.

The current investigation directed to increase the speed and capacity of the computers is centered mainly in the improvement of the technology of the integrated circuits and in the development of even quicker commutation components. Circuits have been built integrated to great scale that they contain several millions of components in a single chip You has ended up manufacturing computers that reach towering speeds in which the semiconductors are replaced by circuits semiconductor that use the unions of Josephson that work to next temperatures to the absolute zero.

'Electronic circuits'

Circuit oscillator

The illustration presents the simplified schematic diagram of a circuit oscillator. The syntonized circuit contains a reel inductive L, another reel smaller inductive L2 and a condenser C.

'Electronic circuits'

Circuits of digital logic and of door NOR

The computers or computers use the digital logic to make operations. The digital logic implies respectively to make successive decisions of true or false that are represented as 1 and 0. The logical circuits that are in the heart of the chips of the computer, are designed to take series of this type of decisions through meetings denominated doors. These are designed and organized in such a way that can take different types of decisions about the entrances that receive. The individual values of entrance and of exit they are always true or false, and they are transmitted through the circuit in form of different tensions. This circuit uses 4 doors NOR, each one of those which not adopts the decision TO non B. The operation NOR gives an exit of 0 as a result every time that one or more than the exit values it is similar to 1. The chart shows the entrance values (TO, B) and of exit (F) of the door NOR. The diagram of the circuit (below) it shows the disposition of a door NOR and their components, indicating the values of tension when the entrances are 0,0 and the exit is 1.

'Electronic circuits'

Uses of the electronic devices

The electronic devices are used as tools in many areas of the advanced investigation. In the illustration we see a microscope of sweeping electrons that uses electrons to generate an image very enlarged in a computer screen.